AU2016209217A1 - DNV magnetic field detector - Google Patents

Abstract

A system for magnetic detection includes a nitrogen vacancy (NV) diamond material comprising a plurality of NV centers, a radio frequency (RF) excitation source configured to provide RF excitation to the NV diamond material, an optical excitation source configured to provide optical excitation to the NV diamond material, an optical detector configured to receive an optical signal emitted by the NV diamond material, and a controller. The optical signal is based on hyperfine states of the NV diamond material. The controller is configured to detect a gradient of the optical signal based on the hyperfine states emitted by the NV diamond material.

Description

DNV MAGNETIC FIELD DETECTOR

CROSS-REFERENCE TO RELATED PATENT APPLICATION

[0001] This application claims the benefit of priority from U.S. Provisional Patent

Application No. 62/257,988, filed November 20, 2015, which is incorporated herein by reference in its entirety. This application claims priority to U.S. Provisional Application No. 62/190,209, filed on July 8, 2015, which is incorporated herein by reference in its entirety. The present application claims priority to co-pending U.S. Application No. 62/261,643, filed December 1, 2015, which is incorporated by reference herein in its entirety. The present application claims the benefit of U.S. Provisional Application Nos. 62/109,006, filed January 28, 2015, and 62/109,551, filed January 29, 2015, each of which is incorporated by reference herein in its entirety. The present application claims the benefit of U.S. Provisional Application No. 62/214,792, filed September 4, 2015, which is incorporated by reference herein in its entirety. This application claims the benefit of priority from U.S. Provisional Patent Application No. 62/258,003, filed November 20, 2015, which is incorporated herein by reference in its entirety. This application claims the benefit of priority from U.S. Provisional Patent Application No. 62/190,218, filed July 8, 2015, which is incorporated herein by reference in its entirety. This application claims the benefit of priority to U.S. Patent Application No. 62/107,289, filed January 23, 2015, which is incorporated by reference herein in its entirety. This application claims priority to U.S. Application No. 15/003,558, filed January 21, 2016, titled “APPARATUS AND METHOD FOR HYPERSENSITIVITY DETECTION OF MAGNETIC FIELD,” which is incorporated by reference herein in its entirety. This application claims priority to U.S. Application No. 15/003,062, filed January 21, 2016, titled “IMPROVED LIGHT COLLECTION FROM DNV SENSORS,” which is incorporated by reference herein in its entirety. This application claims priority to U.S. Application No. 15/003,652, filed January 21, 2016, titled “PRECISION POSITION ENCODER/SENSOR USING NITROGEN VACANCY DIAMOND,” which is incorporated by reference herein in its entirety. This application claims priority to U.S. Application No. 15/003,677, filed January 21, 2016, titled “COMMUNICATION VIA A MAGNIO,” which is incorporated by reference herein in its entirety. This application claims priority to U.S. Application No. 15/003,678, filed January 21, 2016, titled “METHOD claims priority to U.S. Application No. 15/003,177, filed January 21, 2016, titled “HYDROPHONE,” which is incorporated by reference herein in its entirety. This application claims priority to U.S. Application No. 15/003,206, filed January 21, 2016, titled “MAGNETIC NAVIGATION METHODS AND SYSTEMS UTILIZING POWER GRID AND COMMUNICATION NETWORK,” which is incorporated by reference herein in its entirety. The present application claims priority to co-pending U.S. Application No. 15/003,193, filed January 21, 2016, titled “RAPID HIGH-RESOLUTION MAGNETIC FIELD MEASUREMENTS FOR POWER LINE INSPECTION,” which is incorporated by reference herein in its entirety. The present application is also related to co-pending U.S. Application No. 15/003,088, filed January 21, 2016, titled “IN-SITU POWER CHARGING”, which is incorporated by reference herein in its entirety. This application claims priority to co-pending U.S. Application No. 15/003,519, filed January 21, 2016, titled “APPARATUS AND METHOD FOR CLOSED LOOP PROCESSING FOR A MAGNETIC DETECTION SYSTEM”, which is incorporated by reference herein in its entirety. The present application claims priority to copending U.S. Application No. 15/003,718, filed January 21, 2016, titled “APPARATUS AND METHOD FOR RECOVERY OF THREE DIMENSIONAL MAGNETIC FIELD FROM A MAGNETIC DETECTION SYSTEM”, which is incorporated by reference herein in its entirety. The present application claims priority to co-pending U.S. Application No. 15/003,209, filed January 21, 2016, titled "DIAMOND NITROGEN VACANCY SNESED FERRO-FLUID HYDROPHONE," which is incorporated by reference herein in its entirety. The present application claims priority to co-pending U.S. Application No. 15/003,670, filed January 21, 2016, titled " AC VECTOR MAGNETIC ANOMALY DETECTION WITH DIAMOND NITROGEN VACANCIES," which is incorporated by reference herein in its entirety. The present application claims priority to co-pending U.S. Application No. 15/003,704, filed January 21, 2016, titled " APPARATUS AND METHOD FOR ESTIMATING ABSOLUTE AXES’ ORIENTATIONS FOR A MAGNETIC DETECTION SYSTEM," which is incorporated by reference herein in its entirety. The present application claims priority to co-pending U.S. Application No. 15/003,590, filed January 21, 2016, titled " APPARATUS AND METHOD FOR HIGH SENSITIVITY MAGNETOMETRY MEASUREMENT AND SIGNAL PROCESSING IN A MAGNETIC DETECTION SYSTEM," which is incorporated by reference herein in its entirety. The present application claims priority to co-pending U.S. Application No. 15/003,176, filed January 21, 2016, titled " MAGNETIC BAND-PASS FILTER," which is incorporated by reference herein in its entirety. The present application claims priority to copending U.S. Application No. 15/003,145, filed January 21, 2016, titled " DEFECT DETECTOR FOR CONDUCTIVE MATERIALS," which is incorporated by reference herein in its entirety. The present application claims priority to co-pending U.S. Application No. 15/003,309, filed January 21, 2016, titled " DIAMOND NITROGEN VACANCY SENSOR WITH DUAL RF SOURCES," which is incorporated by reference herein in its entirety. The present application claims priority to co-pending U.S. Application No. 15/003,298, filed January 21, 2016, titled " DIAMOND NITROGEN VACANCY SENSOR WITH COMMON RF AND MAGNETIC FIELDS GENERATOR," which is incorporated by reference herein in its entirety. The present application claims priority to co-pending U.S. Application No. 15/003,292, filed January 21, 2016, titled " MAGNETOMETER WITH A LIGHT EMITTING DIODE," which is incorporated by reference herein in its entirety. The present application claims priority to co-pending U.S. Application No. 15/003,281, filed January 21, 2016, titled " MAGNETOMETER WITH LIGHT PIPE," which is incorporated by reference herein in its entirety. The present application claims priority to co-pending U.S. Application No. 15/003,634, filed January 21, 2016, titled " DIAMOND WITH CIRCUITRY FOR USE IN A DIAMOND NITROGEN VACANCY SENSOR," which is incorporated by reference herein in its entirety. The present application claims priority to co-pending U.S. Application No. 15/003,577, filed January 21, 2016, titled " MEASUREMENT PARAMETERS FOR QC METROLOGY OF SYNTHETICALLY GENERATED DIAMOND WITHNV CENTERS," which is incorporated by reference herein in its entirety. The present application claims priority to co-pending U.S. Application No. 15/003,256, filed January 21, 2016, titled " HIGHER MAGNETIC SENSITIVITY THROUGH FLUORESCENCE MANIPULATION BY PHONON SPECTRUM CONTROL," which is incorporated by reference herein in its entirety. The present application claims priority to copending U.S. Application No. 15/003,396, filed January 21, 2016, titled " MAGNETIC WAKE DETECTOR," which is incorporated by reference herein in its entirety. The present application claims priority to co-pending U.S. Application No. 15/003,617, filed January 21, 2016, titled " GENERAL PURPOSE REMOVAL OF GEOMAGNETIC NOISE," which is incorporated by reference herein in its entirety. The present application claims priority to co-pending U.S. Application No. 15/003,336, filed January 21, 2016, titled " REDUCED INSTRUCTION SET CONTROLLER FOR DIAMOND NITROGEN VACANCY SENSOR," which is incorporated by reference herein in its entirety. The present application claims priority to co-pending U.S.

Application No. 15/003,_, filed January 21, 2016, titled "DNV MAGNETIC FIELD DETECTOR," which is incorporated by reference herein in its entirety.

FIELD

[0002] The present disclosure generally relates to magnetometers.

BACKGROUND

[0003] Atomic-sized nitrogen-vacancy (NV) centers in diamond lattices have been shown to have excellent sensitivity for magnetic field measurement and enable fabrication of small magnetic sensors that can readily replace existing-technology (e.g., Hall-effect, SERF, SQUID, or the like) systems and devices. Nitrogen vacancy diamond (DNV) magnetometers are able to sense extremely small magnetic field variations by changes in the diamond's red photoluminescence that relate, through the gradient of the luminescent function, to frequency and thereafter to magnetic field through the Zeeman effect.

BRIEF DESCRIPTION OF THE DRAWINGS

[0004] FIG. 1 illustrates one orientation of an NV center in a diamond lattice.

[0005] FIG. 1 illustrates one orientation of an NV center in a diamond lattice.

[0006] FIG. 2 is an energy level diagram showing energy levels of spin states for the NV center.

[0007] FIG. 3 is a schematic illustrating an NV center magnetic sensor system.

[0008] FIG. 4 is a graph illustrating a fluorescence as a function of an applied RF frequency of an NV center along a given direction for a zero magnetic field.

[0009] FIG. 5 is a graph illustrating the fluorescence as a function of an applied RF freauencv for four different NV center orientations for a non-zero magnetic field.

[0010] FIG. 6 is a schematic diagram illustrating a magnetic field detection system according to an embodiment of the present invention.

[0011] FIG. 7 is a graph illustrating a fluorescence as a function of an applied RF frequency for an NV center orientation in a non-zero magnetic field and a gradient of the fluorescence as a function of the applied RF frequency.

[0012] FIG. 8 is an energy level diagram showing a hyperfine structure of spin states for the NV center.

[0013] FIG. 9 is a graph illustrating a fluorescence as a function of an applied RF frequency for an NV center orientation in a non-zero magnetic field with hyperfine detection and a gradient of the fluorescence as a function of the applied RF frequency.

[0014] FIG. 10 is an overview of a reflector with a diamond having nitrogen vacancies.

[0015] FIG. 11 is a side view of an ellipsoidal reflector with a diamond having nitrogen vacancies and a photo detector.

[0016] FIG. 12 is a side view of an ellipsoidal diamond having nitrogen vacancies and a photo detector.

[0017] FIG. 13 is a side view of a parabolic reflector with a diamond having nitrogen vacancies and a photo detector.

[0018] FIG. 14 is a side view of a parabolic diamond having nitrogen vacancies and a photo detector.

[0019] FIG. 15 is a side view of a parabolic reflector with a flat diamond having nitrogen vacancies inserted parallel to a major axis of the parabolic reflector and a photo detector.

[0020] FIG. 16 is a side view of a parabolic reflector with a flat diamond having nitrogen vacancies inserted parallel to a minor axis of the parabolic reflector and a photo detector.

[0021] FIG. 17 is a side view of a sensor assembly with a parabolic diamond having nitrogen vacancies and a photo detector.

[0022] FIG. 18 is a side view of a sensor assembly with a waveguide provided within a parabolic reflector.

[0023] FIG. 19 is a process diagram for a method for constructing a DNV sensor.

[0024] FIG. 20 is another process diagram for a method for constructing a DNV sensor.

[0025] FIG. 21 is a block diagram depicting a general architecture for a computer system that may be employed to implement various elements of the systems and methods described and illustrated herein.

[0026] FIG. 22 is a schematic illustrating a position sensor system according to one embodiment.

[0027] FIG. 23 is a schematic illustrating a position sensor system including a rotary position encoder.

[0028] FIG. 24 is a schematic illustrating a top down view of a rotary position encoder.

[0029] FIG. 25 is a schematic illustrating a position sensor system including a linear position encoder.

[0030] FIG. 26 is a schematic illustrating a magnetic element arrangement of a position encoder according to one embodiment.

[0031] FIG. 27 is a schematic illustrating a magnetic element arrangement of a position encoder according to another embodiment.

[0032] FIG. 28 is a schematic illustrating a magnetic element arrangement of a position encoder according to another embodiment.

[0033] FIG. 29 is a schematic illustrating the relationship of a position sensor head and the magnetic elements of a position encoder.

[0034] FIG. 30 is a graph of measured magnetic field intensity attributable to magnetic elements of a position encoder for a first magnetic field sensor and a second magnetic field sensor of a position sensor head.

[0035] FIG. 31 is a flow chart illustrating the process of determining a position utilizing a position sensor system according to one embodiment.

[0036] FIGs. 32A and 32B are graphs illustrating the frequency response of a DNV sensor in accordance with an illustrative embodiment.

[0037] FIGs. 33A is a diagram of NV center spin states in accordance with an illustrative embodiment.

[0038] FIG. 33B is a graph illustrating the frequency response of a DNV sensor in response to a changed magnetic field in accordance with an illustrative embodiment.

[0039] FIG. 34 is a block diagram of a magnetic communication system in accordance with an illustrative embodiment.

[0040] FIGs. 35A and 35B show the strength of a magnetic field versus frequency in accordance with an illustrative embodiment.

[0041] FIG. 36 is a block diagram of a computing device in accordance with an illustrative embodiment.

[0042] FIG. 37 is graphs illustrating the fluorescence as a function of applied RF frequency of four different NV center orientations for a magnetic field applied in opposite directions to the NV center diamond material.

[0043] FIG. 38 is a graph illustrating the fluorescence intensity as a function of time for a NV center diamond material with a pulsed RF excitation.

[0044] FIG. 39 is a graph illustrating the fluorescence as a function of applied RF frequency of four different NV center orientations for a magnetic field applied in opposite directions to the NV center diamond material, with a Lorentzian pair being identified in the graph.

[0045] FIG. 40 is a graph illustrating the fluorescence intensity as a function of time for a NV center diamond material for a pulse of RF excitation.

[0046] FIG. 41 is a graph illustrating the normalized fluorescence intensity as a function of time for a pair of Lorentzian peaks of a NV center diamond material.

[0047] FIG. 42 is a graph illustrating the time to 60% of the equilibrium fluorescence as a function of RF frequency for a negative and positive magnetic bias field applied to a NV center diamond material.

[0048] FIGs. 43 A and 43B are diagrams illustrating hydrophone systems in accordance with illustrative embodiments.

[0049] FIG. 44 illustrates a low altitude flying object in accordance with some illustrative implementations.

[0050] FIG. 45A illustrates a ratio of signal strength of two magnetic sensors, A and B, attached to wings of the UAS as a function of distance, x, from a center line of a power in accordance with some illustrative implementations.

[0051] FIG. 45B illustrates a composite magnetic field (B-filed) in accordance with some illustrative implementations.

[0052] FIG. 46 illustrates a high-level block diagram of an example UAS navigation system in accordance with some illustrative implementations.

[0053] FIG. 47 illustrates an example of a power line infrastructure.

[0054] FIGs. 48A and 48B illustrate examples of magnetic field distribution for overhead power lines and underground power cables.

[0055] FIG. 49 illustrates examples of magnetic field strength of power lines as a function of distance from the centerline.

[0056] FIG. 50 illustrates an example of a UAS equipped with DNV sensors in accordance with some illustrative implementations.

[0057] FIG. 51 illustrates a plot of a measured differential magnetic field sensed by the DNV sensors when in close proximity of the power lines in accordance with some illustrative implementations.

[0058] FIG. 52 illustrates an example of a measured magnetic field distribution for normal power lines and power lines with anomalies according to some implementations.

[0059] FIG. 53 is a depiction of the energy levels of an NV center which contribute to the Hamiltonian thereof.

[0060] FIG. 54 is a graph illustrating fluorescence as a function of applied RF frequency of an NV center for a zero external magnetic bias field.

[0061] FIG. 55 is a graph illustrating fluorescence as a function of applied RF frequency of a high quality NV center sample for an applied external magnetic bias field.

[0062] FIG. 56 is a graph illustrating fluorescence as a function of applied RF frequency of a low quality NV center sample for an applied external magnetic bias field.

[0063] FIG. 57 is a signal flow block diagram of an open loop processing of the total incident magnetic field on the NV center magnetic sensor system.

[0064] FIG. 58 is a signal flow block diagram of a closed loop processing of the total incident magnetic field on the NV center magnetic sensor system.

[0065] FIG. 59 is a flowchart showing a method of the closed loop processing of FIG. 58.

[0066] FIG. 60 is a schematic diagram illustrating a magnetic field detection system arrnrrlina an pmtarlimpnt rvf flip nrpQpnt invpntinn [0067] FIG. 61 is a schematic illustrating a Ramsey sequence of optical excitation pulses and RF excitation pulses according to an operation of the system of FIG. 60.

[0068] FIG. 62A is a free induction decay curve where a free precession time τ is varied using the Ramsey sequence of FIG. 61.

[0069] FIG. 62B is a magnetometry curve where a RF detuning frequency Δ is varied using the Ramsey sequence of FIG. 61.

[0070] FIG. 63 A is a free induction decay surface plot where both the free precession time τ and the RF detuning frequency Δ are varied using the Ramsey sequence of FIG.61.

[0071] FIG. 63B is a plot showing a gradient of the free induction decay surface plot of FIG. 63B.

[0072] FIG. 64 is a schematic illustrating a Rabi sequence of optical excitation pulses and RF pulses according to an operation of the system of FIG. 60.

[0073] FIG. 65 is a comparison of graphs showing resonant Rabi frequencies according to a power of RF excitation applied to the system of FIG. 60.

[0074] FIG. 66 is a graph showing raw pulse data collected during an operation of the system of FIG. 60.

[0075] FIG. 67 is a schematic illustrating a portion of a DNV sensor with a coil assembly in accordance with some illustrative implementations.

[0076] FIG. 68 is a schematic illustrating a cross section of a portion of a DNV sensor with a coil assembly in accordance with some illustrative implementations.

[0077] FIGS. 69A and 69B are schematics illustrating a coil assembly in accordance with some illustrative implementations.

[0078] FIG. 70 is a cross section illustrating a coil assembly in accordance with some illustrative implementations.

[0079] FIG. 71 is a schematic illustrating a side element of a coil assembly in accordance with some illustrative implementations.

[0080] FIG. 72 is a schematic illustrating a top or bottom element of a coil assembly in accordance with some illustrative implementations.

[0081] FIG. 73 is a schematic illustrating a center mounting block of a coil assembly in accordance with some illustrative implementations.

[0082] FIG. 74 is a cross section illustrating of a portion of a DNV sensor with a coil assembly in accordance with some illustrative implementations.

[0083] FIG. 75 is a schematic illustrating a coil assembly in accordance with some illustrative implementations.

[0084] FIG. 76 is a schematic illustrating a cross section of a coil assembly in accordance with some illustrative implementations.

[0085] FIG. 77 is a schematic illustrating a side element of a coil assembly in accordance with some illustrative implementations.

[0086] FIG. 78 is a schematic illustrating a portion of a DNV sensor with a coil assembly in accordance with some illustrative implementations.

[0087] FIG. 79 is a schematic illustrating a cross section of a portion of a DNV sensor with a coil assembly in accordance with some illustrative implementations.

[0088] FIG. 80 is a schematic illustrating a cross section of a portion of a DNV sensor with a coil assembly in accordance with some illustrative implementations.

[0089] FIG. 81 is a schematic illustrating a coil assembly in accordance with some illustrative implementations.

[0090] FIG. 82 is a schematic illustrating a cross section of a coil assembly in accordance with some illustrative implementations.

[0091] FIG. 83 is a schematic illustrating a side element of a coil assembly in accordance with some illustrative implementations.

[0092] FIGs. 84A and 84B are schematics illustrating top and bottom elements of a coil assembly in accordance with some illustrative implementations.

[0093] FIG. 85 illustrates a geomagnetic noise model compared with empirical noise data.

[0094] FIG. 86 is a graph illustrating a signal of interest due to a distortion in the magnetic field in the Z-direction as measured by a single magnetic sensor.

[0095] FIGs. 87A-87C are graphs illustrating the signal of interest due to a distortion in the magnetic field in the Z-direction as measured by a two-dimensional magnetic sensor array for times of 1100, 1115 and 1120 seconds, respectively.

[0096] FIG. 88 is a schematic illustrating a magnetic sensor array system according to an embodiment of the invention.

[0097] FIGs. 89A and 89B respectively illustrate a common coordinate system and a coordinate system corresponding to one of the magnetic sensors of the array.

[0098] FIG. 90 is a schematic illustrates an orientation sensor attached to a magnetic field sensor according to an embodiment of the invention.

[0099] FIGs. 91A-91C are graphs illustrating a magnetic field measurement component along the X-direction, Y-direction and Z-direction, respectively, at a time of 500 seconds for a two-dimensional array of magnetic field sensors in the case of a single unmanned underwater vehicle (UUV).

[00100] FIGs. 91D-91F are graphs illustrating a magnetic field measurement component along the X-direction, Y-direction and Z-direction, respectively, at a time of 1000 seconds for a two-dimensional array of magnetic field sensors in the case of a single UUV.

[00101] FIGs. 91G-91I are graphs illustrating a magnetic field measurement component along the X-direction, Y-direction and Z-direction, respectively, at a time of 1500 seconds for a twodimensional array of magnetic field sensors in the case of a single UUV.

[00102] FIGs. 92A-92C are graphs illustrating a magnetic field measurement component along the X-direction, Y-direction and Z-direction, respectively, at a time of 500 seconds for a two-dimensional array of magnetic field sensors in the case of two UUVs.

[00103] FIGs. 92D-92F are graphs illustrating a magnetic field measurement component along the X-direction, Y-direction and Z-direction, respectively, at a time of 1000 seconds for a two-dimensional array of magnetic field sensors in the case of two UUVs.

[00104] FIGs. 92G-92I are graphs illustrating a magnetic field measurement component along the X-direction, Y-direction and Z-direction, respectively, at a time of 1500 seconds for a twodimensional array of magnetic field sensors in the case of two UUVs.

[00105] FIG. 93 A is a graph illustrating the X-direction component of the noise free and measured magnetic fields as a function of time for a single magnetic field sensor measurement.

[00106] FIG. 93B is a graph illustrating the noise free and reconstructed X-direction component of the magnetic field as a function of time for a single magnetic field sensor measurement as a function of time, where the noise has been removed by a median subtraction algorithm.

[00107] FIG. 93C is a graph illustrating the difference in the noise free and reconstructed X-direction component of the magnetic fields of FIG. 93B.

[00108] FIGs. 94A-94C are graphs illustrating the magnetic field for an array of sensors including the signal of interest in the X-direction for the array at times of 500, 1000 and 1500 seconds, respectively.

[00109] FIGs. 95A-95C are graphs illustrating, in the X-direction, a region of interest and a expanded region of interest as a results of set closing and convex hulling, at respective times of 500, 1000 and 1500 seconds for a single UUV.

[00110] FIGs. 96A-96C are graphs illustrating a fit to a plane of the X-direction component of magnetic field measurement data with the region of interest data removed for a two-dimensional array of magnetic field sensors at times of 500, 1000 and 1500 seconds, respectively.

[00111] FIG. 97A is a graph illustrating the X-direction component of noise free and measured magnetic fields as a function of time for a single magnetic field sensor measurement.

[00112] FIG. 97B is a graph illustrating the noise free and reconstructed X-direction component of the magnetic field as a function of time for a single magnetic field sensor measurement as a function of time, where the noise has been removed using noise fit to a plane.

[00113] FIG. 97C is a graph illustrating the difference in the noise free and reconstructed X-direction component of the magnetic field of FIG. 97B.

[00114] FIGs. 98A-98C are graphs illustrating a fit to a quadratic spline of the X-direction component of magnetic field measurement data with the region of interest data removed for a two-dimensional array of magnetic field sensors at times of 500, 1000 and 1500 seconds, respectively.

[00115] FIG. 99A is a graph illustrating the X-direction component of noise free and measured magnetic fields as a function of time for a single magnetic field sensor measurement.

[00116] FIG. 99B is a graph illustrating the noise free and reconstructed X-direction component of the magnetic field as a function of time for a single magnetic field sensor measurement as a function of time, where the noise has been removed using noise fit to a quadratic spline.

[00117] FIG. 99C is a graph illustrating the difference in the noise free and reconstructed X-direction component of the magnetic field of FIG. 99B.

[00118] FIGs. 100A-100C are graphs illustrating, in the X-direction, a region of interest and a expanded region of interest as a results of set closing and convex hulling, at respective times of 500, 1000, and 1500 seconds fortwoUUVs.

[00119] FIGs. 101A-101C are graphs illustrating a fit to a quadratic spline of the X-direction component of magnetic field measurement data with the region of interest data removed for a two-dimensional array of magnetic field sensors at times of 500, 1000 and 1500 seconds, respectively, for two UUVs.

[00120] FIG. 102A is a graph illustrating X-direction component of noise free and measured magnetic fields as a function of time for a single magnetic field sensor measurement for two UUVs.

[00121] FIG. 102B is a graph illustrating the noise free and reconstructed X-direction component of the magnetic field as a function of time for a single magnetic field sensor measurement as a function of time, where the noise has been removed using noise fit to a quadratic spline.

[00122] FIG. 102C is a graph illustrating the difference in the noise free and reconstructed X-direction component of the magnetic field of FIG. 102B.

[00123] FIG. 103 A is a top perspective view of a sensor assembly according to an embodiment of the invention.

[00124] FIG. 103B is a bottom perspective view of the sensor assembly of FIG. 103 A.

[00125] FIG. 104A is a top perspective view of a diamond assembly of the sensor assembly of FIG. 103 A.

[00126] FIG. 104B is a bottom perspective view of the diamond assembly of FIG. 104A.

[00127] FIG. 104C is a side view of an assembly substrate of the sensor assembly of FIG. 104 A.

[00128] FIG. 105 is a top view of the diamond assembly of FIG. 104A.

[00129] FIG. 106A and 106B are side views of diamond material with metal layers illustrating steps of forming a RF excitation source according to an embodiment.

[00130] FIG. 107A is a top view of the diamond assembly according to another embodiment.

[00131] FIG. 107B is a side view of the diamond assembly if FIG. 107A.

[00132] FIG. 108 is a graphical diagram depicting NV0 and NV- photon intensity relative to wavelength without fluorescence manipulation.

[00133] FIG. 109 is a graphical diagram for the indirect band gap for a diamond having nitrogen vacancies depicting a valence band and a conduction band on an energy versus momentum (E vs. k) plot and showing a zero phonon line, an optical drive for exciting an electron over the band gap, and the recombination of the electron from various points of the conduction band to generate photons.

[00134] FIG. 110 is a graphical diagram depicting NV0 and NV- photon intensity relative to wavelength with fluorescence manipulation.

[00135] FIG. 111 is a process diagram for fluorescence manipulation of the diamond having nitrogen vacancies through phonon spectrum manipulation using an acoustic driver.

[00136] FIG. 112 is a process diagram for determining an acoustic driving frequency for phonon spectrum manipulation.

[00137] FIG. 113 A is a block diagram of a magnetometer with a light pipe in accordance with an illustrative embodiment.

[00138] FIGs. 113B and 113C are isometric views of a light pipe and a shield in accordance with illustrative embodiments.

[00139] FIG. 114 is a block diagram of a magnetometer with two light pipes in accordance with an illustrative embodiment.

[00140] FIG. 115 is a block diagram of a magnetometer with two light pipes in accordance with an illustrative embodiment.

[00141] FIG. 116 is a flow diagram of a method for measuring a magnetic field in accordance with an illustrative embodiment.

[00142] FIG. 117 is a block diagram of a magnetometer in accordance with an illustrative embodiment.

[00143] FIG. 118 is an exploded view of a magnetometer in accordance with an illustrative embodiment.

[00144] FIG. 119 is a flow diagram of a method for detecting a magnetic field in accordance with an illustrative embodiment.

[00145] FIG 120 is a schematic illustrating a portion of a DNV sensor with a dual RF arrangement in accordance with some illustrative implementations.

[00146] FIG. 121 is a view of an enclosed DNV sensor with a dual RF arrangement in accordance with some illustrative implementations.

[00147] FIGs. 122A and 122B are schematics of an assembly portion of a DNV sensor with a dual RF arrangement in accordance with some illustrative implementations.

[00148] FIG. 123 is a cross-section of a portion of a DNV sensor with a dual RF arrangement in accordance with some illustrative implementations.

[00149] FIG. 124 is a schematic illustrating a DNV sensor with a dual RF arrangement in accordance with some illustrative implementations.

[00150] FIG. 125 is a cross-section of a DNV sensor with a dual RF arrangement in accordance with some illustrative implementations.

[00151] FIG. 126 is a schematic illustrating a DNV sensor with a dual RF arrangement and laser mounting in accordance with some illustrative implementations.

[00152] FIG. 127 is a cross-section of a DNV sensor with a dual RF arrangement and laser mounting in accordance with some illustrative implementations.

[00153] FIGs. 128 A and 128B are schematics of an assembly portion of a DNV sensor with a dual RF arrangement in accordance with some illustrative implementations.

[00154] FIGs. 129A and 129B are schematics of an assembly portion of a DNV sensor with a dual RF arrangement in accordance with some illustrative implementations.

[00155] FIG. 130 is a block diagram of an overview of a single-cycle synthesis, control, and acquisition system for a diamond nitrogen vacancy sensor.

[00156] FIG. 131 is a block circuit diagram of the single-cycle control, synthesis, and acquisition processor for a diamond nitrogen vacancy sensor of FIG. 130.

[00157] FIG. 132A is a block circuit diagram of the host interface of FIG. 131.

[00158] FIG. 132B is a block circuit diagram of the program counter of FIG. 131.

[00159] FIG. 132C is a block circuit diagram of the program memory of FIG. 131.

[00160] FIG. 132D is a block circuit diagram of a first portion of the jump control with delay of FIG. 131.

[00161] FIG. 132E is a block circuit diagram of a second portion of the jump control FIG. 131.

[00162] FIG. 132F is a block circuit diagram of the RF waveform generator of FIG. 131.

[00163] FIG. 132G is a block circuit diagram of the digital control of FIG. 131.

[00164] FIG. 132H is a block circuit diagram of the acquisition processor of FIG. 131.

[00165] FIG. 133A is a unit cell diagram of the crystal structure of a diamond lattice having a standard orientation.

[00166] FIG. 133B is a unit cell diagram of the crystal structure of a diamond lattice having an unknown orientation.

[00167] FIG. 134 is a schematic diagram illustrating a step in a method for determining the unknown orientation of the diamond lattice of FIG. 133B.

[00168] FIG. 135 is a flowchart illustrating a sign recovery method for the method for determining the unknown orientation of the diamond lattice of FIG. 133B.

[00169] FIG. 136 is a schematic diagram illustrating a step in the method for determining the unknown orientation of the diamond lattice of FIG. 133B.

[00170] FIG. 137 is a flowchart illustrating a method for recovering a three-dimensional magnetic field on the NV center magnetic sensor system.

[00171] FIG. 138 is an overview diagram of a diamond of a DNV sensor with a low pass filter and a high pass filter.

[00172] FIG. 139 is graphical diagram of an example signal detected with a DNV sensor that includes a test signal without filtering.

[00173] FIG. 140 is an overview diagram of a diamond of a DNV sensor with a low pass filter and showing a magnetic field of the environment, a change in the magnetic field of the environment, and an induced magnetic field by the low pass filter to filter high frequency signals.

[00174] FIG. 141 is another overview diagram of a diamond of a DNV sensor with two low pass filters arranged for spatial attenuation.

[00175] FIG. 142 is an overview diagram of a diamond of a DNV sensor relative to a diamagnetic material and showing alignment of the poles of the diamagnetic material relative to the induced magnetic field.

[00176] FIG. 143 is a graphical diagram of magnetism in a diamagnetic material relative to the applied magnetic field.

[00177] FIG. 144 is a process diagram for modifying a filtering frequency of a low pass filter for a DNV sensor based on a detected magnetic field.

[00178] FIG. 145 is a process diagram for modifying an orientation of a DNV sensor with a low pass filter based on a detected magnetic field.

[00179] FIG. 146 illustrates a low altitude flying object in accordance with some illustrative implementations.

[00180] FIG. 147 illustrates a magnetic field detector in accordance with some illustrative implementations.

[00181] FIGs. 148 A and 148B illustrate a portion of a detector array in accordance with some illustrative implementations.

[00182] FIG. 149 is a schematic illustrating a hydrophone in accordance with some illustrative implementations.

[00183] FIG. 150 is a schematic illustrating a portion of a vehicle with a hydrophone in accordance with some illustrative implementations.

[00184] FIG. 151 is a schematic illustrating a portion of a vehicle with a hydrophone with a containing membrane in accordance with some illustrative implementations.

[00185] FIG. 152 is a schematic illustrating a portion of a vehicle with a hydrophone in accordance with some illustrative implementations.

[00186] FIG. 153 is a schematic illustrating a portion of a vehicle with a hydrophone with a containing membrane in accordance with some illustrative implementations.

[00187] FIG. 154 is a schematic illustrating a system for AC magnetic vector anomaly detection according to an embodiment of the invention.

[00188] FIG. 155 is a schematic illustrating a sequence of optical excitation pulses and RF pulses according to the operation of the system of FIG. 156.

[00189] FIG. 156 is a graph illustrating the fluorescence signal of NV diamond material as a function of RF excitation frequency over an range of RF frequencies according to an embodiment of the invention.

[00190] FIG. 157A illustrates a matched-filtered first correlated code for the magnetic field component along three different diamond lattice directions corresponding to the magnetic field provided by a first magnetic field generator according to an embodiment of the invention.

[00191] FIG. 157B illustrates a matched-filtered first correlated code for the magnetic field component along three different diamond lattice directions corresponding to the magnetic field provided by a second magnetic field generator according to an embodiment of the invention.

[00192] FIG. 158 illustrates reconstructed magnetic field vectors for two different correlated codes in the case where a ferrous object and no object are disposed in relation to a magnetic field generator and NV diamond material, according to an embodiment of the invention.

[00193] FIGs. 159A and 159B are block diagrams of a system for detecting deformities in a material in accordance with an illustrative embodiment.

[00194] FIGs. 160 illustrates current paths through a conductor with a deformity in accordance with an illustrative embodiment.

[00195] FIGs. 161 is a flow diagram of a method for detecting deformities in accordance with an illustrative embodiment.

[00196] FIG. 162 is a block diagram of a vehicular system in accordance with an illustrative embodiment.

[00197] FIG. 163 is a flow chart of a method for charging a power source in accordance with an illustrative embodiment.

[00198] FIG. 164 is a graph of the strength of a magnetic field versus distance from the conductor in accordance with an illustrative embodiment.

[00199] FIGs. 165 A and 165B are block diagrams of a system for detecting deformities in transmission lines in accordance with an illustrative embodiment.

[00200] FIG. 166 illustrates current paths through a transmission line with a deformity in accordance with an illustrative embodiment.

[00201] FIG. 167 illustrates power transmission line sag between transmission towers in accordance with an illustrative embodiment.

[00202] FIG. 168 illustrates vector measurements indicating power transmission line sag in accordance with an illustrative embodiment.

[00203] FIG. 169 illustrates vector measurements along a path between adjacent towers in accordance with an illustrative embodiment.

DETAILED DESCRIPTION

[00204] HYPERSENSITIVITY DETECTION OF MAGNETIC FIELD

[00205] Aspects of the disclosure relates to apparatuses and methods for elucidating hyperfine transition responses to determine an external magnetic field acting on a magnetic detection system. The hyperfine transition responses exhibit a steeper gradient than the gradient of aggregate Lorentzian responses measured in conventional systems, which can be up to three orders of magnitude larger. The steeper gradient exhibited by the hyperfine transition responses thus allow for a comparable increase in measurement sensitivity in a magnetic detection system. By utilizing the largest gradient of the hyperfine responses for measuring purposes, external magnetic fields may be detected more accurately, especially low magnitude and/or rapidly changing fields.

[00206] The NV Center, Its Electronic Structure, and Optical and RF Interaction [00207] The NV center in a diamond comprises a substitutional nitrogen atom in a lattice site adjacent a carbon vacancy as shown in FIG. 1. The NV center may have four orientations, each corresponding to a different crystallographic orientation of the diamond lattice.

[00208] The NV center may exist in a neutral charge state or a negative charge state. Conventionally, the neutral charge state uses the nomenclature NV°, while the negative charge state uses the nomenclature NV, which is adopted in this description.

[00209] The NV center has a number of electrons, including three unpaired electrons, each one from the vacancy to a respective of the three carbon atoms adjacent to the vacancy, and a pair of electrons between the nitrogen and the vacancy. The NV center, which is in the negatively charged state, also includes an extra electron.

[00210] The NV center has rotational symmetry, and as shown in FIG. 2, has a ground state, which is a spin triplet with 3A2 symmetry with one spin state ms = 0, and two further spin states ms = +1, and ms = -1. In the absence of an external magnetic field, the ms = ±1 energy levels are offset from the ms = 0 due to spin-spin interactions, and the ms = ±1 energy levels are degenerate, i.e., they have the same energy. The ms = 0 spin state energy level is split from the ms = ±1 energy levels by an energy of 2.87 GHz for a zero external magnetic field.

[00211] Introducing an external magnetic field with a component along the NV axis lifts the degeneracy of the ms = ±1 energy levels, splitting the energy levels ms = ±1 by an amount 2gpBBz, where g is the g-factor, μΒ is the Bohr magneton, and Bz is the component of the external magnetic field along the NV axis. This relationship is correct to a first order and inclusion of higher order corrections is straightforward matter and will not affect the computational and logic steps in the systems and methods described below.

[00212] The NV center electronic structure further includes an excited triplet state 3E with corresponding ms = 0 and ms = ±1 spin states. The optical transitions between the ground state 3A2 and the excited triplet 3E are predominantly spin conserving, meaning that the optical transitions are between initial and final states that have the same spin. For a direct transition between the excited triplet 3E and the ground state 3A2, a photon of red light is emitted with a photon energy corresponding to the energy difference between the energy levels of the transitions.

[00213] There is, however, an alternative non-radiative decay route from the triplet 3E to the ground state 3A2 via intermediate electron states, which are thought to be intermediate singlet states A, E with intermediate energy levels. Significantly, the transition rate from the ms = ±1 spin states of the excited triplet 3E to the intermediate energy levels is significantly greater than the transition rate from the ms = 0 spin state of the excited triplet 3E to the intermediate energy levels. The transition from the singlet states A, E to the ground state triplet 3A2 predominantly decays to the ms = 0 spin state over the ms = ±1 spins states. These features of the decay from the excited triplet 3E state via the intermediate singlet states A, E to the ground state triplet 3A2 allows that if optical excitation is provided to the system, the optical excitation will eventually pump the NV center into the ms = 0 spin state of the ground state 3A2. In this way, the population of the ms = 0 spin state of the ground state 3A2 may be “reset” to a maximum polarization determined by the decay rates from the triplet 3E to the intermediate singlet states.

[00214] Another feature of the decay is that the fluorescence intensity due to optically stimulating the excited triplet 3E state is less for the ms = ±1 states than for the ms = 0 spin state. This is so because the decay via the intermediate states does not result in a photon emitted in the fluorescence band, and because of the greater probability that the ms = ±1 states of the excited triplet 3E state will decay via the non-radiative decay path. The lower fluorescence intensity for the ms = ±1 states than for the ms = 0 spin state allows the fluorescence intensity to be used to determine the spin state. As the population of the ms = ±1 states increases relative to the ms = 0 spin, the overall fluorescence intensity will be reduced.

[00215] The NV Center, or Magneto-Optical Defect Center, Magnetic Sensor System [00216] FIG. 3 is a schematic diagram illustrating a conventional NV center magnetic sensor system 300 that uses fluorescence intensity to distinguish the ms = ±1 states, and to measure the magnetic field based on the energy difference between the ms = +1 state and the ms = -1 state. The system 300 includes an optical excitation source 310, which directs optical excitation to an NV diamond material 320 with NV centers. The system further includes an RF excitation source [00217] The RF excitation source 330 may be a microwave coil, for example. The RF excitation source 330, when emitting RF radiation with a photon energy resonant with the transition energy between ground ms = 0 spin state and the ms = +1 spin state, excites a transition between those spin states. For such a resonance, the spin state cycles between ground ms = 0 spin state and the ms = +1 spin state, reducing the population in the ms = 0 spin state and reducing the overall fluorescence at resonances. Similarly, resonance occurs between the ms = 0 spin state and the ms = -1 spin state of the ground state when the photon energy of the RF radiation emitted by the RF excitation source is the difference in energies of the ms = 0 spin state and the ms = -1 spin state, or between the ms = 0 spin state and the ms = +1 spin state, there is a decrease in the fluorescence intensity.

[00218] The optical excitation source 310 may be a laser or a light emitting diode, for example, which emits light in the green, for example. The optical excitation source 310 induces fluorescence in the red, which corresponds to an electronic transition from the excited state to the ground state. Light from the NV diamond material 320 is directed through the optical filter 350 to filter out light in the excitation band (in the green, for example), and to pass light in the red fluorescence band, which in turn is detected by the detector 340. The optical excitation light source 310, in addition to exciting fluorescence in the diamond material 320, also serves to reset the population of the ms = 0 spin state of the ground state 3A2 to a maximum polarization, or other desired polarization.

[00219] For continuous wave excitation, the optical excitation source 310 continuously pumps the NV centers, and the RF excitation source 330 sweeps across a frequency range that includes the zero splitting (when the ms = ±1 spin states have the same energy) energy of 2.87 GHz. The fluorescence for an RF sweep corresponding to a diamond material 320 with NV centers aligned along a single direction is shown in FIG. 4 for different magnetic field components Bz along the NV axis, where the energy splitting between the ms = -1 spin state and the ms = +1 spin state increases with Bz. Thus, the component Bz may be determined. Optical excitation schemes other than continuous wave excitation are contemplated, such as excitation schemes involving pulsed optical excitation, and pulsed RF excitation. Examples of pulsed excitation schemes include Ramsey pulse sequence, and spin echo pulse sequence.

[00220] In general, the diamond material 320 will have NV centers aligned along directions of four different orientation classes. FIG. 5 illustrates fluorescence as a function of RF frequency for the case where the diamond material 320 has NV centers aligned along directions of four different orientation classes. In this case, the component Bz along each of the different orientations may be determined. These results, along with the known orientation of crystallographic planes of a diamond lattice, allow not only the magnitude of the external magnetic field to be determined, but also the direction of the magnetic field.

[00221] While FIG. 3 illustrates an NV center magnetic sensor system 300 with NV diamond material 320 with a plurality of NV centers, in general, the magnetic sensor system may instead employ a different magneto-optical defect center material, with a plurality of magneto-optical defect centers. The electronic spin state energies of the magneto-optical defect centers shift with magnetic field, and the optical response, such as fluorescence, for the different spin states is not the same for all of the different spin states. In this way, the magnetic field may be determined based on optical excitation, and possibly RF excitation, in a corresponding way to that described above with NV diamond material.

[00222] FIG. 6 is a schematic diagram of a system 600 for a magnetic field detection system according to an embodiment of the present invention. The system 600 includes an optical excitation source 610, which directs optical excitation to an NV diamond material 620 with NV centers, or another magneto-optical defect center material with magneto-optical defect centers.

An RF excitation source 630 provides RF radiation to the NV diamond material 620.

[00223] As shown in FIG. 6, a first magnetic field generator 670 generates a magnetic field, which is detected at the NV diamond material 620. The first magnetic field generator 670 may be a permanent magnet positioned relative to the NV diamond material 620, which generates a known, uniform magnetic field (e.g., a bias or control magnetic field) to produce a desired fluorescence intensity response from the NV diamond material 620. In some embodiments, a second magnetic field generator 675 may be provided and positioned relative to the NV diamond material 620 to provide an additional bias or control magnetic field. The second magnetic field generator 675 may be configured to generate magnetic fields with orthogonal polarizations, for example. In this regard, the second magnetic field generator 675 may include one or more coils, such as a Helmholtz coils. The coils may be configured to provide relatively uniform magnetic fields at the NV diamond material 620 and each may generate a magnetic field having a direction that is orthogonal to the direction of the magnetic field generated by the other coils. For example, in a particular embodiment, the second magnetic field generator 675 may include three Helmholtz coils that are arranged to each generate a magnetic field having a direction orthogonal to the other direction of the magnetic field generated by the other two coils resulting in a three-axis magnetic field. In some embodiments, only the first magnetic field generator 670 may be provided to generate a bias or control magnetic field. Alternatively, only the second magnetic field generator 675 may be provided to generate the bias or control magnetic field. In yet other embodiments, the first and/or second magnetic field generators may be affixed to a pivot assembly (e.g., a gimbal assembly) that may be controlled to hold and position the first and/or second magnetic field generators to a predetermined and well-controlled set of orientations, thereby establishing the desired bias or control magnetic fields. In this case, the controller 680 may be configured to control the pivot assembly having the first and/or second magnetic field generators to position and hold the first and/or second magnetic field generators at the predetermined orientation.

[00224] The system 600 further includes a controller 680 arranged to receive a light detection or optical signal from the optical detector 640 and to control the optical excitation source 610, the RF excitation source 630, and the second magnetic field generator 675. The controller may be a single controller, or multiple controllers. For a controller including multiple controllers, each of the controllers may perform different functions, such as controlling different components of the system 600. The second magnetic field generator 675 may be controlled by the controller 680 via an amplifier 660, for example.

[00225] The RF excitation source 630 may be a microwave coil, for example. The RF excitation source 630 is controlled to emit RF radiation with a photon energy resonant with the [00226] The optical excitation source 610 may be a laser or a light emitting diode, for example, which emits light in the green, for example. The optical excitation source 610 induces fluorescence in the red from the NV diamond material 620, where the fluorescence corresponds to an electronic transition from the excited state to the ground state. Light from the NV diamond material 620 is directed through the optical filter 650 to filter out light in the excitation band (in the green, for example), and to pass light in the red fluorescence band, which in turn is detected by the optical detector 640. The optical excitation light source 610, in addition to exciting fluorescence in the NV diamond material 620, also serves to reset the population of the ms = 0 spin state of the ground state 3A2 to a maximum polarization, or other desired polarization.

[00227] The controller 680 is arranged to receive a light detection signal from the optical detector 640 and to control the optical excitation source 610, the RF excitation source 630, and the second magnetic field generator 675. The controller may include a processor 682 and a memory 684, in order to control the operation of the optical excitation source 610, the RF excitation source 630, and the second magnetic field generator 675. The memory 684, which may include a nontransitory computer readable medium, may store instructions to allow the operation of the optical excitation source 610, the RF excitation source 630, and the second magnetic field generator 675 to be controlled. That is, the controller 680 may be programmed to provide control.

[00228] Detection of Magnetic Field Changes [00229] As discussed above, the interaction of the NV centers with an external magnetic field results in an energy splitting between the ms = -1 spin state and the ms = +1 spin state that increases with Bz as shown in FIG. 4, for example. The pair of frequency responses (also known as Lorentzian responses, profiles, or dips) due to the component of the external magnetic field along the given NV axis manifest as dips in intensity of the emitted red light from the NV centers as a function of RF carrier frequency. Accordingly, a pair of frequency responses for each of the four axes of the NV center diamond lattice result in an energy splitting between the ms = -1 spin state and the ms = +1 spin state that corresponds to the component of the external magnetic field along the axis for a total of eight Lorentzian profiles or dips, as shown in FIG. 5. When a bias magnetic field is applied to the NV diamond material (such as by the first and/or second magnetic field generators 670, 675 of FIG. 6), in addition to an unknown external magnetic field existing outside the system, the total incident magnetic field may thus be expressed as Bt(t) = ^fcias(f) + Bext(t), where Bbias(t) represents the bias magnetic field applied to the NV diamond material and Bext(t) represents the unknown external magnetic field. This total incident magnetic field creates equal and linearly proportional shifts in the Lorentzian frequency profiles for a given NV axis between the ms = -1 spin state and the ms = +1 spin state relative to the starting carrier frequency (e.g., about 2.87 GHz).

[00230] Because the applied bias magnetic field Bbias(t) is already known and constant, a change or shift in the total incident magnetic field Bt(t) will be due to a change in the external magnetic field Bext(t). To detect a change in the total incident magnetic field, the point of greatest sensitivity in measuring such a change will occur at the point where the frequency response is at its largest slope. For example, as shown in FIG. 7, an intensity response /(t) as a function of an RF applied frequency f(t) for a given NV axis due to a magnetic field is shown in the top graph. The change in intensity /(t) relative to the change in RF applied frequency, -pp, is plotted against the RF applied frequency f(t) as shown in the bottom graph. Point 25 represents the point of the greatest gradient of the Lorentzian dip 20. This point gives the greatest measurement sensitivity in detecting changes in the total incident magnetic field as it responds to the external magnetic field.

[00231] The Hyperfine Field [00232] As discussed above and shown in the energy level diagram of FIG. 2, the ground state is split by about 2.87 GHz between the ms = 0 and ms = ±1 spin states due to their spin-spin interactions. In addition, due to the presence of a magnetic field, the ms = ±1 spin states split in proportion to the magnetic field along the given axis of the NV center, which manifests as the four-pair Lorentzian frequency response shown in FIG. 5. However, a hyperfine structure of the NV center exists due to the hyperfine coupling between the electronic spin states of the NV center and the nitrogen nucleus, which results in further energy splitting of the spin states. FIG. 8 shows the hyperfme structure of the ground state triplet 3A2 of the NV center. Specifically, coupling to the nitrogen nucleus 14N further splits the ms = ±1 spin states into three hyperfme transitions (labeled as mi spin states), each having different resonances. Accordingly, due to the hyperfme split for each of the ms = ±1 spin states, twenty-four different frequency responses may be produced (three level splits for each of the ms = ±1 spin states for each of the four NV center orientations).

[00233] Each of the three hyperfme transitions manifest within the width of one aggregate Lorentzian dip. With proper detection, the hyperfme transitions may be elucidated within a given Lorentzian response. To detect such hyperfme transitions, in particular embodiments, the NV diamond material 620 exhibits a high purity (e.g., low existence of lattice dislocations, broken bonds, or other elements beyond 14N) and does not have an excess concentration of NV centers. In addition, during operation of the system 600 in some embodiments, the RF excitation source 630 is operated on a low power setting in order to further resolve the hyperfme responses. In other embodiments, additional optical contrast for the hyperfme responses may be accomplished by increasing the concentration of NV negative-charge type centers, increasing the optical power density (e.g., in a range from about 20 to about 1000 mW/mm2), and decreasing the RF power to the lowest magnitude that permits a sufficient hyperfme readout (e.g., about 1 to about 10 W/mm2).

[00234] FIG. 9 shows an example of fluorescence intensity as a function of an applied RF frequency for an NV center with hyperfme detection. In the top graph, the intensity response /(t) as a function of an applied RF frequency f(t) for a given spin state (e.g., ms = -1) along a given axis of the NV center due to an external magnetic field is shown. In addition, in the bottom graph, the gradien

plotted against the applied RF frequency f(t) is shown. As seen in the figure, the three hyperfme transitions 200a-200c constitute a complete Lorentzian response 20 (e.g., corresponding to the Lorenztian response 20 in FIG. 7). The point of maximum slope may then be determined through the gradient of the fluorescence intensity as a function of the applied RF frequency, which occurs at the point 250 in FIG. 9. This point of maximum slope may then be tracked during the applied RF sweep to detect movement of the point of maximum slope along the frequency sweep. Like the point of maximum slope 25 for the aggregate Lorentzian response, the corresponding movement of the point 250 corresponds to changes in the total incident magnetic field Bt(t), which because of the known and constant bias field Bbias(t), allows for the detection of changes in the external magnetic field Bext(t).

[00235] However, as compared to point 25, point 250 exhibits a larger gradient than the aggregate Lorentzian gradient described above with regard to FIG. 7. In some embodiments, the gradient of point 250 may be up to 1000 times larger than the aggregate Lorentzian gradient of point 25. Due to this, the point 250 and its corresponding movement may be more easily detected by the measurement system resulting in improved sensitivity, especially in very low magnitude and/or very rapidly changing magnetic fields.

[00236] IMPROVED LIGHT COLLECTION FROM DNV SENSORS

[00237] In some aspects of the present technology, methods and configurations are disclosed for an efficient collection of fluorescence (e.g., red light) emitted by the nitrogen vacancies of a diamond of a DNV sensor. In some implementations, the subject technology can allow efficient collection of the emitted light of the diamond of the DNV sensor with a compact and low cost reflector. The reflector can focus the emitted light of the diamond of the DNV sensor to an optical or photo detector that can increase the amount of light detected from the diamond. In some implementations, such a configuration may detect virtually all light emitted by the diamond of the DNV sensor. In some aspects, the reflector may be shaped as a parabola, an ellipse, or other shapes that can convey the light emitted from a source to a focal point or focal area.

[00238] In some other implementations of the subject technology, the diamond of the DNV sensor may be machined or otherwise shaped to be a reflector itself. That is, the diamond with nitrogen vacancies may be shaped to form a parabolic reflector, ellipsoidal reflector or other shapes that can convey the light emitted from the nitrogen vacancies to a focal point or focal area. For example, the reflector can be mostly parabolic or ellipsoidal such that the light hits the photo detector at a 90 degree angle with some margin of error, e.g., 2 to 10 degrees.

[00239] The nitrogen vacancies of the diamond will fluoresce in response to excitation with green light and will emit red light in random directions. Because the red light measurements are shot noise limited, collecting as much emitted light as possible is desirable. In some current collection approaches using large optics, the collection efficiencies were in the range of 20%. Some implementations use a large aperture lens mounted close to the diamond or DNV sensor, which limits light collection to a fraction of the light emitted by the diamond or DNV sensor. Other implementations use a flat diamond and a number of photo detectors (e.g., four) positioned at the edges of the flat diamond. This arrangement of photo detectors may be able to capture more of the emitted light conducted to edges of the flat diamond due to internal reflection, but increases the number of photo detectors required and may not capture light emitted from the faces of the flat diamond. The DNV sensors discussed herein provide an alternative to increase the collection efficiency.

[00240] FIG. 10 depicts an overview of an assembly 1000 with an example diamond 1002 having nitrogen vacancies and a reflector 1004 positioned about the diamond 1002 for a DNV light-collection apparatus. In the implementation shown, the reflector 1004 is positioned about the diamond 1002 to reflect a portion of the light emitted 1006 from the diamond 1002. The reflector 1004 is an elliptical or ellipsoidal reflector with the diamond 1002 positioned within a portion of the reflector 1004. In other implementations, as discussed in further detail herein, the reflector 1004 may be parabolic or any other geometric configuration to reflect light emitted from the diamond 1002. In some implementations, the reflector 1004 may be a monolithic reflector, a hollow reflector, or any other type of reflector to reflect light emitted from the diamond 1002. In the implementation shown, the diamond 1002 is positioned at a focus 1008 of the reflector 1004. Thus, when light 1006 is emitted from the diamond 1002, the light is reflected by the reflector 1004 toward another focus of the reflector 1004. As will be discussed in further detail herein, a photo detector may be positioned at the second focus to collect the reflected light.

[00241] FIG. 11 depicts an assembly 1100 with an example diamond 1102 having nitrogen vacancies and an ellipsoidal reflector 1104 positioned about the diamond 1102 for a DNV light-collection apparatus. In some implementations, the ellipsoidal reflector 1104 can be a single monolithic component that can be considered to be divided into two portions, such as a reflector portion 1106 and a concentrator portion 1108. In other implementations, the ellipsoidal reflector 1104 may be divided into two components, such as the reflector portion 1106 and the concentrator portion 1108 that are coupled and/or otherwise positioned relative to each other. For instance, the reflector portion 1106 and the concentrator portion 1108 may be separate parabolic components that can be combined to form the ellipsoidal reflector 1104. In still further configurations, the ellipsoidal reflector 1104 may be composed of more than two components and can be coupled or otherwise positioned to form the ellipsoidal reflector 1104.

[00242] The diamond 1102 is positioned at a first focus of the ellipsoidal reflector 1104 for the reflector portion 1106. In some implementations, the diamond 1102 is positioned at the first focus using a mount for the diamond 1102. In other implementations, the diamond 1102 is positioned at the first focus using a borehole through the ellipsoidal reflector 1104. The borehole may be backfilled to seal the diamond 1102 in the ellipsoidal reflector 1104.

[00243] The ellipsoidal reflector 1104 may also include an opening to allow an excitation laser beam to excite the diamond 1102, such as a green excitation laser beam. The opening may be positioned at any location for the ellipsoidal reflector 1104. When the diamond 1102 is excited (e.g., by applying green light to the diamond 1102), then the reflector portion 1106 reflects the red light emitted 1110 from the diamond 1102 towards the concentrator portion 1108.

[00244] The concentrator portion 1108 directs the emitted light 1110 toward a second focus of the ellipsoidal reflector 1104. In the implementation shown, a photo detector 1120 is positioned to receive and measure the light from the concentrator portion 1108. In some implementations, the photo detector 1120 is positioned at the second focus to receive the redirected emitted light.

In some implementations the photo detector 1120 is coupled and/or sealed to a portion of the ellipsoidal reflector 1104, such as to the concentrator portion 1108. In some implementations, the opening may be adjacent or proximate to the photo detector 1120, such as through the concentrator portion 1108. In other implementations, the opening may be opposite the photo detector 1120, such as through the reflector portion 1106. In still further configurations, the opening may be at any other angle and/or orientation relative to the photo detector 1120.

[00245] In some implementations, an optical filter, such as a red filter, may be applied to and/or positioned on the photo detector 1120 to filter out light except the relevant red light of interest. Thus, the ellipsoidal reflector 1104 is concatenated with a non-focusing concentrator that can capture the emitted light from a light source (e.g., from the nitrogen vacancies of the diamond of a DNV sensor) to a single photo detector. In some instances, the loss of emitted light can be limited to the light loss due to the mount for the diamond and/or the small entrance for the green stimulation laser beam.

[00246] The foregoing solution provides high light collection efficiency to collect the light emitted from the diamond 1102, while utilizing a reflector 1104 that may not require high precision refinements. Such a reflector 1104 may be a low cost solution to increase the light collection efficiency, such as using a reflective mirror component. In addition, the shape of the ellipsoidal reflector 1104 may separate the electronics of the photo detector 1120 from the diamond 1102, which may decrease the magnetic interaction between the electronics of the photo detector 1120 and the diamond 1102.

[00247] The elliptical reflector 1104 may, in some implementations, include a substrate with a dielectric mirror film or coating applied to reflect the emitted light 1110. The dielectric mirror film may be selected for the specific frequency of interest. In some implementations, the thickness of the dielectric mirror material may affect the specific frequency of interest. For instance, the substrate may possess a high clarity at a frequency of interest for the DNV sensor. The substrate may be made of a plastic, glass, diamond, quartz, and/or any other suitable material. The dielectric mirror film may be applied to the substrate such that the light emitted 1110 from the diamond 1102 is reflected within the ellipsoidal reflector 1104. In some implementations, the dielectric mirror film may only reflect red light such that other colors or wavelengths of light pass through the ellipsoidal reflector 1104. For instance, such a dielectric mirror film may permit transmission of green wavelength light, such as from an excitation laser beam, through the ellipsoidal reflector 1104 to the diamond 1102 to excite the diamond 1102.

[00248] In some aspects, such as for precision sensors, the separation between the diamond 1102 and the electronics of the photo detector 1120 can be extended, for example to several feet.

In some implementations, the thin dielectric mirror film is used in the ellipsoidal reflector 1104 to allow an RF antenna to be located inside the ellipsoidal reflector 1104. In some applications, the antenna may instead be outside of the ellipsoidal reflector 1104.

[00249] FIG. 12 depicts an assembly 1200 with an example diamond 1202 having nitrogen vacancies that is formed or machined into a reflector configuration for a DNV light-collection apparatus. The diamond 1202 in the present configuration is formed or machined into an ellipsoidal reflector and is a monolithic component that can be considered to be divided into two portions, such as a reflector portion 1204 and a concentrator portion 1206.

[00250] The diamond 1202 may have a dielectric mirror film coated on or applied to the diamond 1202. The dielectric mirror film may be selected for the specific frequency of interest. In some implementations, the thickness of the dielectric mirror material may affect the specific frequency of interest. The dielectric mirror film may be applied such that the light emitted 1210 from the nitrogen vacancies within the diamond 1202 is reflected within the reflector portion 1204 and concentrator portion 1206 of the diamond 1202. In some implementations, the dielectric mirror film may only reflect red light such that other colors or wavelengths of light pass through the diamond 1202. For instance, such a dielectric mirror film may permit transmission of green wavelength light, such as from an excitation laser beam, through the dielectric mirror film to the nitrogen vacancies of the diamond 1202 to excite the nitrogen vacancies of the diamond 1202.

[00251] The reflector portion 1204 of the diamond 1202 may internally reflect the emitted light 1210 via the dielectric mirror film applied to the diamond 1202. Thus, the diamond 1202 internally reflects the red light emitted 1210 from the diamond 1202 towards the concentrator portion 1206. The concentrator portion 1206 also redirects the light emitted 1210 by the nitrogen vacancies of the diamond 1202 toward a focus of the concentrator portion 1206 of the diamond 1202. In the implementation shown, a photo detector 1220 is positioned to receive and measure the light from the concentrator portion 1206. In some implementations, the photo detector 1220 is positioned at the focus to receive the redirected emitted light 1210. In some implementations [00252] In some implementations, an optical filter, such as a red filter, may be applied to and/or positioned on the photo detector 1220 to filter out light except the relevant red light of interest.

[00253] In some implementations, a portion of the diamond 1202 may be formed without nitrogen vacancies. That is, for instance, one or more layers for the diamond may be formed by chemical deposition without nitrogen vacancies. The one or more layers may be machined or formed for the concentrator portion such that the emitted light reflected by the reflector portion 1204 is not reabsorbed by nitrogen vacancies when travelling through the concentrator portion 1206 of the diamond 1202.

[00254] FIG. 13 depicts an assembly 1300 with an example diamond 1302 having nitrogen vacancies and a parabolic reflector 1304 positioned about the diamond 1302 for a DNV light-collection apparatus. In some implementations, the parabolic reflector 1304 can be a single monolithic component. In some configurations, the parabolic reflector 1304 may be composed of more than two components and can be coupled or otherwise positioned to form the parabolic reflector 1304.

[00255] The diamond 1302 is positioned at a focus of the parabolic reflector 1304. In some implementations, the diamond 1302 is positioned at the focus using a mount for the diamond 1302. In other implementations, the diamond 1302 is positioned at the focus using a borehole through the parabolic reflector 1304. The borehole may be backfilled to seal the diamond 1302 in the parabolic reflector 1304.

[00256] The parabolic reflector 1304 may also include an opening to allow an excitation laser beam to excite the diamond 1302, such as a green excitation laser beam. The opening may be positioned at any location for the parabolic reflector 1304. When the diamond 1302 is excited (e.g., by applying green light to the diamond 1302), then the parabolic reflector 1304 reflects the red light emitted 1310 from the diamond 1302 towards a photo detector 1320. In the implementation shown, a photo detector 1320 is positioned to receive and measure the light from the parabolic reflector 1304. In some implementations the photo detector 1320 is coupled and/or sealed to a portion of the parabolic reflector 1304. In some implementations, the opening may be adjacent or proximate to the photo detector 1320. In other implementations, the opening may be opposite the photo detector 1320. In still further configurations, the opening may be at any other angle and/or orientation relative to the photo detector 1320.

[00257] In some implementations, an optical filter, such as a red filter, may be applied to and/or positioned on the photo detector 1320 to filter out light except the relevant red light of interest. Thus, the parabolic reflector 1304 is concatenated with a non-focusing concentrator that can capture the emitted light from a light source (e.g., from the nitrogen vacancies of the diamond of a DNV sensor) to a single photo detector. In some instances, the loss of emitted light can be limited to the light loss due to the mount for the diamond and/or the small entrance for the green stimulation laser beam.

[00258] The foregoing solution provides high light collection efficiency to collect the light emitted from the diamond 1302, while utilizing a parabolic reflector 1304 that may not require high precision refinements. Such a parabolic reflector 1304 may be a low cost solution to increase the light collection efficiency, such as using a reflective mirror component. In addition, the shape of the parabolic reflector 1304 may separate the electronics of the photo detector 1320 from the diamond 1302, which may decrease the magnetic interaction between the electronics of the photo detector 1320 and the diamond 1302.

[00259] The parabolic reflector 1304 may, in some implementations, include a substrate with a dielectric mirror film or coating applied to reflect the emitted light 1310. The dielectric mirror film may be selected for the specific frequency of interest. In some implementations, the thickness of the dielectric mirror material may affect the specific frequency of interest. For instance, the substrate may possess a high clarity at a frequency of interest for the DNV sensor. The substrate may be made of a plastic, glass, diamond, quartz, and/or any other suitable material. The dielectric mirror film may be applied to the substrate such that the light emitted 1310 from the diamond 1302 is reflected within the parabolic reflector 1304. In some implementations, the dielectric mirror film may only reflect red light such that other colors or wavelengths of light pass through the parabolic reflector 1304. For instance, such a dielectric mirror film may permit transmission of green wavelength light, such as from an excitation laser beam, through the parabolic reflector 1304 to the diamond 1302 to excite the diamond 1302.

[00260] In some aspects, such as for precision sensors, the separation between the diamond 1302 and the electronics of the photo detector 1320 can be extended, for example to several feet. In some implementations, the thin dielectric mirror film is used in the parabolic reflector 1304 to allow an RF antenna to be located inside the parabolic reflector 1304. In some applications, the antenna may instead be outside of the parabolic reflector 1304.

[00261] FIG. 14 depicts an assembly 1400 with an example diamond 1402 having nitrogen vacancies that is formed or machined into a reflector configuration for a DNV light-collection apparatus. The diamond 1402 in the present configuration is formed or machined into a parabolic reflector and is a monolithic component.

[00262] The diamond 1402 may have a dielectric mirror film coated on or applied to the diamond 1402. The dielectric mirror film may be selected for the specific frequency of interest.

In some implementations, the thickness of the dielectric mirror material may affect the specific frequency of interest. The dielectric mirror film may be applied such that the light emitted 1410 from the nitrogen vacancies within the diamond 1402 is reflected within the diamond 1402. In some implementations, the dielectric mirror film may only reflect red light such that other colors or wavelengths of light pass through the diamond 1402. For instance, such a dielectric mirror film may permit transmission of green wavelength light, such as from an excitation laser beam, through the dielectric mirror film to the nitrogen vacancies of the diamond 1402 to excite the nitrogen vacancies of the diamond 1402.

[00263] The parabolic reflector configuration for the diamond 1402 may internally reflect the emitted light 1410 via the dielectric mirror film applied to the diamond 1402. Thus, the diamond 1402 internally reflects the red light emitted 1410 from the diamond 1402 a photo detector 1420 that is positioned to receive and measure the light emitted. In some implementations the photo detector 1420 is coupled and/or sealed to a portion of the diamond 1402.

[00264] In some implementations, an optical filter, such as a red filter, may be applied to and/or positioned on the photo detector 1420 to filter out light except the relevant red light of interest.

[00265] In some implementations, a portion of the diamond 1402 may be formed without nitrogen vacancies. That is, for instance, one or more layers for the diamond may be formed by chemical deposition without nitrogen vacancies. The one or more layers may be machined or formed near the junction for the photo detector 1420 such that the emitted light reflected by the parabolic reflector configuration of the diamond 1402 is not reabsorbed by nitrogen vacancies when travelling through the one or more layers of the diamond 1402.

[00266] FIG. 15 depicts another implementation of a parabolic reflector configuration for an assembly 1500 for a DNV sensor. An example thin diamond 1502 having nitrogen vacancies may be inserted into a portion of a parabolic reflector 1504 positioned about the diamond 1502 for a DNV light-collection apparatus. In some implementations, the parabolic reflector 1504 can be a single monolithic component that is split into two portions to insert the thin diamond 1502. In some other configurations, the parabolic reflector 1504 may be composed of more than two components and can be coupled or otherwise positioned to form the parabolic reflector 1504. In the implementation shown, the thin diamond 1502 is inserted parallel to (and in some instances along) an axis of symmetry the parabolic reflector 1504. In implementations utilizing an ellipsoidal reflector, the thin diamond 1502 may be inserted parallel to and/or along a major axis of the ellipsoidal reflector.

[00267] The parabolic reflector 1504 may also include an opening to allow an excitation laser beam to excite the diamond 1502, such as a green excitation laser beam. The opening may be positioned at any location for the parabolic reflector 1504. When the diamond 1502 is excited (e.g., by applying green light to the diamond 1502), then the parabolic reflector 1504 reflects the red light emitted 1510 from the diamond 1502 towards a photo detector 1520. In the implementation shown, a photo detector 1520 is positioned to receive and measure the light from the parabolic reflector 1504. In some implementations the photo detector 1520 is coupled and/or sealed to a portion of the parabolic reflector 1504. In some implementations, the opening may be adjacent or proximate to the photo detector 1520. In other implementations, the opening may be opposite the photo detector 1520. In still further configurations, the opening may be at any other angle and/or orientation relative to the photo detector 1520.

[00268] In some implementations, an optical filter, such as a red filter, may be applied to and/or positioned on the photo detector 1520 to filter out light except the relevant red light of interest. Thus, the parabolic reflector 1504 is concatenated with a non-focusing concentrator that can capture the emitted light from a light source (e.g., from the nitrogen vacancies of the diamond of a DNV sensor) to a single photo detector. In some instances, the loss of emitted light can be limited to the light loss due to the mount for the diamond and/or the small entrance for the green stimulation laser beam.

[00269] The foregoing solution provides high light collection efficiency to collect the light emitted from the diamond 1502, while utilizing a parabolic reflector 1504 that may not require high precision refinements. Such a parabolic reflector 1504 may be a low cost solution to increase the light collection efficiency, such as using a reflective mirror component. In addition, the shape of the parabolic reflector 1504 may separate the electronics of the photo detector 1520 from the diamond 1502, which may decrease the magnetic interaction between the electronics of the photo detector 1520 and the diamond 1502.

[00270] The parabolic reflector 1504 may, in some implementations, include a substrate with a dielectric mirror film or coating applied to reflect the emitted light 1510. The dielectric mirror film may be selected for the specific frequency of interest. In some implementations, the thickness of the dielectric mirror material may affect the specific frequency of interest. For instance, the substrate may possess a high clarity at a frequency of interest for the DNV sensor. The substrate may be made of a plastic, glass, diamond, quartz, and/or any other suitable material. The dielectric mirror film may be applied to the substrate such that the light emitted 1510 from the diamond 1502 is reflected within the parabolic reflector 1504. In some implementations, the dielectric mirror film may only reflect red light such that other colors or wavelengths of light pass through the parabolic reflector 1504. For instance, such a dielectric [00271] In some aspects, such as for precision sensors, the separation between the diamond 1502 and the electronics of the photo detector 1520 can be extended, for example to several feet. In some implementations, the thin dielectric mirror film is used in the parabolic reflector 1504 to allow an RF antenna to be located inside the parabolic reflector 1504. In some applications, the antenna may instead be outside of the parabolic reflector 1504.

[00272] FIG. 16 depicts another implementation of a parabolic reflector configuration for an assembly 1600 for a DNV sensor. An example thin diamond 1602 having nitrogen vacancies may be inserted into a portion of a parabolic reflector 1604 positioned about the diamond 1602 for a DNV light-collection apparatus. In some implementations, the parabolic reflector 1604 can be a single monolithic component that is split into two portions to insert the thin diamond 1602. In some other configurations, the parabolic reflector 1604 may be composed of more than two components and can be coupled or otherwise positioned to form the parabolic reflector 1604. In the implementation shown, the thin diamond 1602 is inserted perpendicular to an axis of symmetry the parabolic reflector 1604. In implementations utilizing an ellipsoidal reflector, the thin diamond 1602 may be inserted parallel to and/or along a minor axis of the ellipsoidal reflector. In some implementations, the thin diamond 1602 is positioned at a focus of the parabolic reflector 1604.

[00273] The parabolic reflector 1604 may also include an opening to allow an excitation laser beam to excite the diamond 1602, such as a green excitation laser beam. The opening may be positioned at any location for the parabolic reflector 1604. When the diamond 1602 is excited (e.g., by applying green light to the diamond 1602), then the parabolic reflector 1604 reflects the red light emitted 1610 from the diamond 1602 towards a photo detector 1620. In the implementation shown, a photo detector 1620 is positioned to receive and measure the light from the parabolic reflector 1604. In some implementations the photo detector 1620 is coupled and/or sealed to a portion of the parabolic reflector 1604. In some implementations, the opening may be adjacent or proximate to the photo detector 1620. In other implementations, the opening may be [00274] In some implementations, an optical filter, such as a red filter, may be applied to and/or positioned on the photo detector 1620 to filter out light except the relevant red light of interest. Thus, the parabolic reflector 1604 is concatenated with a non-focusing concentrator that can capture the emitted light from a light source (e.g., from the nitrogen vacancies of the diamond of a DNV sensor) to a single photo detector. In some instances, the loss of emitted light can be limited to the light loss due to the mount for the diamond and/or the small entrance for the green stimulation laser beam.

[00275] The foregoing solution provides high light collection efficiency to collect the light emitted from the diamond 1602, while utilizing a parabolic reflector 1604 that may not require high precision refinements. Such a parabolic reflector 1604 may be a low cost solution to increase the light collection efficiency, such as using a reflective mirror component. In addition, the shape of the parabolic reflector 1604 may separate the electronics of the photo detector 1620 from the diamond 1602, which may decrease the magnetic interaction between the electronics of the photo detector 1620 and the diamond 1602.

[00276] The parabolic reflector 1604 may, in some implementations, include a substrate with a dielectric mirror film or coating applied to reflect the emitted light 1610. The dielectric mirror film may be selected for the specific frequency of interest. In some implementations, the thickness of the dielectric mirror material may affect the specific frequency of interest. For instance, the substrate may possess a high clarity at a frequency of interest for the DNV sensor. The substrate may be made of a plastic, glass, diamond, quartz, and/or any other suitable material. The dielectric mirror film may be applied to the substrate such that the light emitted 1610 from the diamond 1602 is reflected within the parabolic reflector 1604. In some implementations, the dielectric mirror film may only reflect red light such that other colors or wavelengths of light pass through the parabolic reflector 1604. For instance, such a dielectric mirror film may permit transmission of green wavelength light, such as from an excitation laser beam, through the parabolic reflector 1604 to the diamond 1602 to excite the diamond 1602.

[00277] In some aspects, such as for precision sensors, the separation between the diamond 1602 and the electronics of the photo detector 1620 can be extended, for example to several feet. In some implementations, the thin dielectric mirror film is used in the parabolic reflector 1604 to allow an RF antenna to be located inside the parabolic reflector 1604. In some applications, the antenna may instead be outside of the parabolic reflector 1604.

[00278] FIG. 17 depicts an assembly 1700 for a DNV sensor that incorporates the assembly 1400 of FIG. 15 where the diamond 1402 is formed or machined into a parabolic configuration. The assembly 1700 includes the photo detector 1420 coupled to and/or positioned to receive the emitted light 1410 from the diamond 1402. The diamond 1402 includes the dielectric mirror film applied to the diamond 1402 to reflect the emitted red light 1410 within the diamond 1402. In some implementations, the dielectric mirror film may only reflect red light such that other colors or wavelengths of light pass through the diamond 1402. For instance, such a dielectric mirror film may permit transmission of green wavelength light 1710, such as from an excitation laser beam, through the dielectric mirror film to the nitrogen vacancies of the diamond 1402 to excite the nitrogen vacancies of the diamond 1402. The assembly 1700 includes microwave coils about the diamond 1402 such that, if the diamond 1402 is irradiated with microwaves at a certain frequency, then the diamond will cease and/or reduce the emission of red light. A microwave off is performed for the DNV sensor prior to illumination of the diamond 1402 to emit the red light 1410. When the microwave frequency is moved to a different frequency, then the red light emitted is dimmed and the frequency is related to the strength of the magnetic field the DNV sensor is within.

[00279] In some implementations, the green light 1710 from the green laser may be applied through a fiber, rather than the free air, to the diamond 1402. In some implementations, the entire apparatus of FIG. 17 may be as compact as ~ 2 mm. The assembly of the subject technology may be used in a number of applications, for example, in all areas of magnetometry, where DNV magnetometers are employed.

[00280] FIG. 18 depicts another implementation of a reflector configuration for an assembly 1800 for a DNV sensor that includes a waveguide 1830 positioned within the reflector to direct light to a diamond 1802 having nitrogen vacancies. An example diamond 1802 having nitrogen vacancies may be inserted into a portion of a reflector 1804 positioned about the diamond 1802 for a DNV light-collection apparatus. In some implementations, the reflector 1804 may be a parabolic reflector or an ellipsoidal reflector. The reflector 1804 can be a single monolithic component or can be a shell component with a fill, such as plastic or fiber optic material, or without a fill (e.g., empty). In the implementation shown, a waveguide 1830 is formed or inserted along an axis of symmetry of the parabolic reflector 1804. In other implementations, the waveguide 1830 is formed or inserted along a major axis of an ellipsoidal reflector 1804. The waveguide 1830 may be a fiber optic component and/or may simply be a material having a differing refractive index than the reflector 1804 and/or the fill within the reflector 1804.

[00281] The diamond 1802 is positioned at an end of the waveguide 1830 such that an excitation beam, such as green laser light, can be transmitted via the waveguide 1830 to the diamond 1802. When the diamond 1802 is excited (e.g., by applying green light to the diamond 1802), then the reflector 1804 reflects the red light emitted 1810 from the diamond 1802 towards a photo detector 1820. In the implementation shown, a photo detector 1820 is positioned to receive and measure the light from the reflector 1804. In some implementations the photo detector 1820 is coupled and/or sealed to a portion of the reflector 1804. In some implementations, an opening for transmitting the excitation beam is through the photo detector 1820 such that the excitation beam can be transmitted via the waveguide 1830 to the diamond 1802. In other implementations, an emitter to emit light to excite the nitrogen vacancy of the diamond 1802, such as the excitation beam, may be provided at a first end of the waveguide 1830 with the diamond 1802 at a second end of the waveguide 1830. In some implementations, the emitter may be formed and/or positioned within or at a center of the photo detector 1820 to generate and transmit the excitation beam along the waveguide 1830 to the diamond 1802. The photo detector 1820 and emitter may be positioned on a single substrate. Thus, a single chip can include both the photo detector 1820 and the emitter for the excitation beam such that both the illumination and collection can be provided on the single chip.

[00282] In some implementations, an optical filter, such as a red filter, may be applied to and/or positioned on the photo detector 1820 to filter out light except the relevant red light of interest. Thus, the reflector 1804 is concatenated with a non-focusing concentrator that can capture the emitted light from a light source (e.g., from the nitrogen vacancies of the diamond of a DNV sensor) to a single photo detector. In some instances, the loss of emitted light can be limited to the light loss due to the mount for the diamond and/or any emitted light that travels back down the waveguide 1830.

[00283] The foregoing solution provides high light collection efficiency to collect the light emitted from the diamond 1802, while utilizing a reflector 1804 that may not require high precision refinements. Such a reflector 1804 may be a low cost solution to increase the light collection efficiency, such as using a reflective mirror component. In addition, the shape of the parabolic reflector 1804 may separate the electronics of the photo detector 1820 and/or emitter from the diamond 1802, which may decrease the magnetic interaction between the electronics of the photo detector 1820 and/or emitter and the diamond 1802.

[00284] The reflector 1804 may, in some implementations, include a substrate with a dielectric mirror film or coating applied to reflect the emitted light 1810. The dielectric mirror film may be selected for the specific frequency of interest. In some implementations, the thickness of the dielectric mirror material may affect the specific frequency of interest. For instance, the substrate may possess a high clarity at a frequency of interest for the DNV sensor. The substrate may be made of a plastic, glass, diamond, quartz, and/or any other suitable material. The dielectric mirror film may be applied to the substrate such that the light emitted 1810 from the diamond 1802 is reflected within the reflector 1804. In some implementations, the dielectric mirror film may only reflect red light such that other colors or wavelengths of light pass through the reflector 1804.

[00285] In some aspects, such as for precision sensors, the separation between the diamond 1802 and the electronics of the photo detector 1820 can be extended, for example to several feet. In some implementations, the thin dielectric mirror film is used in the reflector 1804 to allow an RF antenna to be located inside the reflector 1804. In some applications, the antenna may instead be outside of the reflector 1804.

[00286] FIG. 19 depicts an implementation of a process 1900 to form a DNV sensor. The process 1900 includes providing a diamond having a nitrogen vacancy (block 1902), machining a portion of the diamond to form a reflector (block 1904), positioning a photo detector relative to the diamond to receive light emitted from the diamond (block 1906), and/or applying a dielectric mirror film coat to a portion of the diamond (block 1908). In some implementations, the process 1900 may include simple providing a diamond having a nitrogen vacancy (block 1902) and applying a dielectric mirror film coat to a portion of the diamond (block 1908).

[00287] In some implementations, the machining of the diamond to form a reflector (block 1904) may machine a portion of the diamond to form a parabolic shape, an ellipsoidal shape, and/or any other suitable shape. In some implementations, a layer of the diamond may not have nitrogen vacancies.

[00288] FIG. 20 depicts another process 2000 to form a DNV sensor. The process 2000 includes providing a diamond having a nitrogen vacancy and a reflector (block 2002), positioning the diamond within the reflector such that the reflector reflects a portion of the light from the diamond (block 2004), and/or positioning a photo detector relative to the diamond to receive light emitted from the diamond (block 2006).

[00289] In some implementations, the reflector is monolithic and the diamond is positioned within a borehole of the monolithic reflector. In some implementations, the borehole may be backfilled. In some implementations, the reflector may be formed from two or more pieces and positioning the diamond within the reflector includes inserting the diamond between the two or more pieces. In some instances, the diamond may be substantially flat, such as in the configuration shown in FIGS. 15-16. The two or more pieces of the reflector may be parabolic in shape. The diamond may be positioned parallel to an axis of symmetry of the parabolic reflector or may be positioned perpendicular to the axis of symmetry. In other implementations, the two or more pieces of the reflector may be ellipsoidal in shape. The diamond may be positioned parallel to a major axis of the ellipsoidal reflector or may be positioned parallel to a minor axis of the ellipsoidal reflector. In some further implementations, positioning the diamond within the reflector may include casting the reflector about the diamond.

[00290] FIG. 21 is a diagram illustrating an example of a system 2100 for implementing some aspects of the subject technology. In some implementations, the system 2100 may be a processing system for processing the data output from a photo detector of the implementations describe in reference to FIGS. 11-19. The system 2100 includes a processing system 2102, which may include one or more processors or one or more processing systems. A processor can be one or more processors. The processing system 2102 may include a general-purpose processor or a specific-purpose processor for executing instructions and may further include a machine-readable medium 2119, such as a volatile or non-volatile memory, for storing data and/or instructions for software programs. The instructions, which may be stored in a machine-readable medium 2110 and/or 2119, may be executed by the processing system 2102 to control and manage access to the various networks, as well as provide other communication and processing functions. The instructions may also include instructions executed by the processing system 2102 for various user interface devices, such as a display 2112 and a keypad 2114. The processing system 2102 may include an input port 2122 and an output port 2124. Each of the input port 2122 and the output port 2124 may include one or more ports. The input port 2122 and the output port 2124 may be the same port (e.g., a bi-directional port) or may be different ports.

[00291] The processing system 2102 may be implemented using software, hardware, or a combination of both. By way of example, the processing system 2102 may be implemented with one or more processors. A processor may be a general-purpose microprocessor, a microcontroller, a Digital Signal Processor (DSP), an Application Specific Integrated Circuit (ASIC), a Field Programmable Gate Array (FPGA), a Programmable Logic Device (PLD), a controller, a state machine, gated logic, discrete hardware components, or any other suitable device that can perform calculations or other manipulations of information.

[00292] A machine-readable medium can be one or more machine-readable media. Software shall be construed broadly to mean instructions, data, or any combination thereof, whether referred to as software, firmware, middleware, microcode, hardware description language, or otherwise. Instructions may include code (e.g., in source code format, binary code format, executable code format, or any other suitable format of code).

[00293] Machine-readable media (e.g., 2119) may include storage integrated into a processing system such as might be the case with an ASIC. Machine-readable media (e.g., 2110) may also include storage external to a processing system, such as a Random Access Memory (RAM), a flash memory, a Read Only Memory (ROM), a Programmable Read-Only Memory (PROM), an Erasable PROM (EPROM), registers, a hard disk, a removable disk, a CD-ROM, a DVD, or any other suitable storage device. Those skilled in the art will recognize how best to implement the described functionality for the processing system 2102. According to one aspect of the disclosure, a machine-readable medium is a computer-readable medium encoded or stored with instructions and is a computing element, which defines structural and functional interrelationships between the instructions and the rest of the system, which permit the instructions’ functionality to be realized. Instructions may be executable, for example, by the processing system 2102 or one or more processors. Instructions can be, for example, a computer program including code for performing methods of the subject technology.

[00294] A network interface 2116 may be any type of interface to a network (e.g., an Internet network interface), and may reside between any of the components shown in FIG. 21 and coupled to the processor via the bus 2104.

[00295] A device interface 2118 may be any type of interface to a device and may reside between any of the components shown in FIG. 21. A device interface 2118 may, for example, be an interface to an external device (e.g., USB device) that plugs into a port (e.g., USB port) of the system 2100. In some implementations, the device interface 2118 may be an interface to the apparatus of FIGS. 10-18, where some or all of the analysis of the detected red light by the photo detector electronics is handled by the processing system 2102.

[00296] The foregoing description is provided to enable a person skilled in the art to practice the various configurations described herein. While the subject technology has been particularly described with reference to the various figures and configurations, it should be understood that these are for illustration purposes only and should not be taken as limiting the scope of the subject technology.

[00297] One or more of the above-described features and applications may be implemented as software processes that are specified as a set of instructions recorded on a computer readable storage medium (alternatively referred to as computer-readable media, machine-readable media, or machine-readable storage media). When these instructions are executed by one or more processing unit(s) (e.g., one or more processors, cores of processors, or other processing units), they cause the processing unit(s) to perform the actions indicated in the instructions. In one or more implementations, the computer readable media does not include carrier waves and electronic signals passing wirelessly or over wired connections, or any other ephemeral signals. For example, the computer readable media may be entirely restricted to tangible, physical objects that store information in a form that is readable by a computer. In one or more implementations, the computer readable media is non-transitory computer readable media, computer readable storage media, or non-transitory computer readable storage media.

[00298] In one or more implementations, a computer program product (also known as a program, software, software application, script, or code) can be written in any form of programming language, including compiled or interpreted languages, declarative or procedural languages, and it can be deployed in any form, including as a stand-alone program or as a module, component, subroutine, object, or other unit suitable for use in a computing environment. A computer program may, but need not, correspond to a file in a file system. A program can be stored in a portion of a file that holds other programs or data (e.g., one or more scripts stored in a markup language document), in a single file dedicated to the program in question, or in multiple coordinated files (e.g., files that store one or more modules, sub programs, or portions of code). A computer program can be deployed to be executed on one computer or on multiple computers that are located at one site or distributed across multiple sites and interconnected by a communication network.

[00299] While the above discussion primarily refers to microprocessor or multi-core processors that execute software, one or more implementations are performed by one or more integrated circuits, such as application specific integrated circuits (ASICs) or field programmable gate arrays (FPGAs). In one or more implementations, such integrated circuits execute instructions that are stored on the circuit itself.

[00300] In one or more implementations, the subject technology is directed to method and systems for an efficient collection of fluorescence (e.g., red light) emitted by the NV centers of a DNV sensor. In some aspects, the subject technology may be used in various markets, including for example and without limitation, advanced sensors and materials and structures.

[00301] PRECISION POSITION ENCODER/SENSOR USING NITROGEN VACANCY DIAMOND

[00302] A position sensor system may include a position sensor that includes a magnetic field sensor. The magnetic field sensor may be a DNV magnetic field sensor capable of resolving a magnetic field vector of the type described above. The high sensitivity of the DNV magnetic field sensor combined with an appropriate position encoder component is capable of resolving both a discrete position and a proportionally determined position between discrete positions. The position sensor system has a small size, light weight, and low power requirement.

[00303] As shown in FIG. 22, the position sensor 2220 may be part of a system that also includes an actuator 2210 and a sensor component 2230. The actuator 2210 may be connected to the position sensor 2220 by any appropriate attachment means 2214, such as a rod or shaft. The actuator may be any actuator that produces the desired motion, such as an electro-mechanical actuator. The position sensor 2220 may be connected to the sensor component 2230 by any appropriate attachment means 2224, such as a rod or shaft. A controller 2240 may be included in the system and connected to the position sensor 2220 and optionally the actuator 2210 by electronic interconnects 2222 and 2212, respectively. The controller may be configured to receive a measured position from the position sensor 2220 and activate or deactivate the actuator to position the sensor 2230 in a desired position. According to one embodiment the controller may be on the same substrate as the magnetic field sensor of the position sensor. The controller may include a processor and a memory.

[00304] The position sensor may be a rotary position sensor. FIG. 23 depicts a rotary position sensor system that includes a rotary actuator 2380 that is configured to produce a rotation of a sensor 2390. A rotary position encoder 2310 is connected to the rotary actuator 2380 by a connection means 2382, such as a rod or shaft. A connection means 2392 is also provided between the rotary position encoder 2310 and the sensor 2390. A position sensor head 2320 is located to measure the magnetic field of magnetic elements located on the rotary position encoder 2310. The position sensor head 2320 is aligned with magnetic elements located on the rotary position encoder 2310 at a distance, r, from the center of the rotary position encoder. A surface of the rotary position encoder 2310 that includes magnetic elements is shown in FIG. 24. The center 2440 of the rotary position encoder 2310 may be configured to attach to a connection means 2392, 2394 that connects the rotary position encoder 2310 to the actuator 2320 or the sensor 2390. Magnetic elements, such as uniform coarse magnetic elements 2434 and tapered fine magnetic elements 2432, may be disposed on the surface of the rotary position encoder 2310 along an arc 2436 at a distance, r, from the center of the rotary position encoder. The magnetic elements on the rotary position encoder 2310 may be located on only a portion of the arc, as shown in FIG. 24, or around an entirety of the arc forming a circle of magnetic elements.

[00305] The spacing between the magnetic elements on the rotary position encoder 2310 correlates to a discrete angular rotation, Θ. The distance between magnetic elements associated with the discrete angular rotation, Θ, increases as r increases. The sensitivity of the magnetic field sensors employed in the position sensor allows r to be reduced while maintaining a high degree of precision for the angular position of the rotary position encoder. The rotary position encoder may have an r on the order of mm, such as an r of 1 mm to about 30 mm, or about 5 mm to about 20 mm. The rotary position encoder allows for the measurement of a rotary position with a precision of 0.5 micro-radians.

[00306] The position sensor may be a linear position sensor. As shown in FIG. 25, the linear position sensor system includes a linear actuator 2580 that is configured to produce linear motion of the linear position encoder 2510 and sensor 2590. The linear position encoder 2510 may be connected to the linear actuator by a connecting means 2582, such as a rod or shaft. The linear position encoder 2510 may be connected to the sensor 2590 by a connecting means 2592, such as a rod or shaft. A position sensor head 2520 is located to measure the magnetic field produced by magnetic elements disposed on the linear position encoder. In some cases, a mechanical linkage, such as a lever arm, may be utilized to multiply the change in position of the linear position encoder for an associated movement of the sensor. The linear position sensor may have a sensitivity that allows a change in position on the order of hundreds of nanometers to be resolved, such as a position change of 500 nm.

[00307] The magnetic elements may be arranged on the linear or rotary position encoder in any appropriate configuration. As shown in FIG. 26, the magnetic elements may include both uniform coarse magnetic elements 2634 and tapered fine magnetic elements 2632. The uniform coarse magnetic elements 2634 may have an influence on the local magnetic field that is at least two orders of magnitude greater than the maximum influence of the tapered fine magnetic elements 2634. The coarse magnetic elements 2634 may be formed on the position encoder by any suitable process. According to one embodiment, a polymer loaded with magnetic material may be utilized to form the uniform coarse magnetic elements. The amount of magnetic material that may be included in the coarse magnetic elements is limited by potential interference with other elements in the system.

[00308] The tapered fine magnetic elements may be formed by any suitable process on the position encoder. According to one embodiment, a polymer loaded with magnetic material may be utilized to form the tapered fine magnetic elements. The loading of the magnetic material in the polymer may be increased to produce a magnetic field gradient from a first end of the tapered fine magnetic element to a second end of the tapered fine magnetic element. Alternatively, the geometric size of the tapered fine magnetic element may be increased to create the desired magnetic field gradient. A magnetic field gradient of the tapered fine magnetic element may be about 10 nT/mm. The tapered fine magnetic elements 2632 as shown in FIG. 26 allow positions between the coarse magnetic elements 2634 to be accurately resolved. The position encoder on which the magnetic elements are disposed may be formed from any appropriate material, such as a ceramic, glass, polymer, or non-magnetic metal material.

[00309] The size of the magnetic elements is limited by manufacturing capabilities. The magnetic elements on the position encoder may have geometric features on the order of nanometers, such as about 5 nm.

[00310] FIG. 27 depicts an alternate magnetic element arrangement that may be employed when the additional precision provided by the tapered fine magnetic elements is not required.

The magnetic element arrangement of FIG. 27 includes only coarse magnetic elements 2634. FIG. 13 depicts a magnetic element arrangement that does not include coarse magnetic elements. A similar effect to the coarse magnetic elements 2634 may be achieved by utilizing the transitions between the maximum of the tapered fine magnetic elements 2632 and the minimum of the adjacent tapered fine magnetic elements as indicators in much the same way that the coarse magnetic elements shown in FIGS. 26 and 27 indicate a discrete change in position.

While FIGS. 26-18 depict the magnetic element arrangements in linear form, similar magnetic element arrangements may be applied to a rotary position encoder.

[00311] According to an alternative embodiment, a single tapered magnetic element may be employed. Such an arrangement may be especially suitable for an application where only a small position range is required, as for a larger position range the increase in magnetic field with the increasing gradient of the magnetic element may interfere with other components of the position sensor system. The use of a single tapered magnetic element may allow a position to be determined without first initializing the position sensor by setting the position encoder to a known position. The ability of the magnetic field sensor to resolve a magnetic field vector may allow a single magnetic field sensor to be employed in the position sensor head when a single tapered fine magnetic element is utilized on the position encoder.

[00312] The position sensor head 2620 may include a plurality of magnetic field sensors, as shown in FIG. 29. For magnetic element arrangements including more than one element, at least two magnetic field sensors 2624 and 2622 may be utilized in the position head sensor. The magnetic field sensors may be separated by a distance, a. The distance, a, between the magnetic sensors 2622 and 2624 may be less than the distance, d, between the coarse magnetic elements 2634. According to one embodiment, the relationship between the spacing of the magnetic field sensors and the spacing of the coarse magnetic elements may be 0. Id < a < d. As shown in FIG. 29, the position sensor head 2620 may include a third and fourth magnetic field sensor. The magnetic field sensors in the position sensor head may be DNV magnetic field sensors of the type described above.

[00313] The magnetic field sensor arrangement in the position sensor head 2620 depicted in FIG. 29 allows the direction of movement of the position encoder to be determined. As shown in FIG. 30, the spacing between the magnetic field sensors 2624 and 2622 produces a delayed response to the magnetic field elements as the position encoder moves. The difference in measured magnetic field for each magnetic field sensor allows a direction of the movement of the position encoder to be determined, as for any given position of the position encoder a different output magnetic field will be measured by each magnetic field sensor. The increasing portion of the plots in FIG. 30 is produced by the tapered fine magnetic element and the square peak is produced by the coarse magnetic element. These measured magnetic fields may be utilized to determine the change in position of the position encoder, and thereby the sensor connected to the position encoder.

[00314] The controller of the position sensor system may be programmed to determine the position of position encoder, and thereby the sensor connected thereto, utilizing the output from the magnetic field sensors. As shown in FIG. 31, the controller may include a line transection logic 402 function that determines when the coarse magnetic elements have passed the magnetic sensor. The output from two magnetic field sensors B1 and B2 may be utilized to determine the direction of the position change based on the order in which a coarse magnetic element is encountered by the magnetic field sensors, and to count the number of coarse magnetic elements measured by the magnetic field sensors. Each coarse magnetic element adds a known amount of position change due to the known spacing between the coarse magnetic elements on the position encoder. An element gradient logic processing function 400 is programmed in the controller to determine the position between coarse magnetic elements based on the magnetic field signal produced by the tapered fine magnetic elements located between the coarse magnetic elements. As shown in FIG. 31, the element gradient logic processing 400 is utilized only when the line transection logic determines that the position is between coarse magnetic elements, or lines. In the case that the position is determined to be between coarse magnetic elements, a position correction, δθ, is calculated based on the magnetic field associated with the tapered fine magnetic elements. The position correction is then added to the sum of the position change calculated from the number of coarse magnetic elements that were counted. A final position may be calculated by [00315] The position sensor may be employed in a method for controlling the position of the position encoder. The method includes determining a movement direction required to reach a desired position, and activating the actuator to produce the desired movement. The position sensor is employed to monitor the change in position of the position encoder, and determine when to deactivate the actuator and stop the change in position. The change in position may be stopped once the desired position is reached. The method may additionally include initializing the position sensor system by moving the position encoder to a known starting point. The end position of the position encoder may be determined after the deactivation of the actuator, and the end position may be stored in a memory of the position sensor controller as a starting position for future movement.

[00316] The ability of the position sensor system to resolve positions between the coarse magnetic elements of the position encoder provides many practical benefits. For example, the position of the position encoder, and associated sensor, may be known with more precision while reducing the size, weight and power requirements of the position sensor system. Additionally, position control systems that offer resolution of discrete position movements can result in dithering when a desired position is between two discrete position values. Dithering can result in unwanted vibration and overheating of the actuator as the control system repeatedly tries to reach the desired position.

[00317] The characteristics of the position sensor system described above make it especially suitable for applications where precision, size, weight, and power requirements are important considerations. The position sensor system is well suited for astronautic applications, such as on space vehicles. The position sensor system is also applicable to robot arms, 3-d mills, machine tools, and X-Y tables.

[00318] The position sensor system may be employed to control the position of a variety of sensors and other devices. Non-limiting examples of sensors that could be controlled with the position sensor system are optical sensors.

[00319] COMMUNICATION VIA A MAGNIO

[00320] Radio waves can be used as a carrier for information. Thus, a transmitter can modulate radio waves at one location, and a receiver at another location can detect the modulated radio waves and demodulate the signals to receive the information. Many different methods can be used to transmit information via radio waves. However, all such methods use radio waves as a carrier for the information being transmitted.

[00321] However, radio waves are not well suited for all communication methods. For example, radio waves can be greatly attenuated by some materials. For example, radio waves do not generally travel well through water. Thus, communication through water can be difficult using radio waves. Similarly, radio waves can be greatly attenuated by the earth. Thus, wireless communication through the earth, for example for coal or other mines, can be difficult. It is often difficult to communicate wirelessly via radio waves from a metal enclosure. The strength of a radio wave signal can also be reduced as the radio wave passes through materials such as walls, trees, or other obstacles. Additionally, communication via radio waves is widely used and understood. Thus, secret communication using radio waves requires complex methods and devices to maintain the secrecy of the information.

[00322] According to some embodiments described herein, wireless communication is achieved without using radio waves as a carrier for information. Rather, modulated magnetic fields can be used to transmit information. For example, a transmitter can include a coil or inductor. When current passes through the coil, a magnetic field is generated around the coil.

The current that passes through the coil can be modulated, thereby modulating the magnetic field. Accordingly, information converted into a modulated electrical signal (e.g., the modulated current through the coil) can be used to transfer the information into a magnetic field. A magnetometer can be used to monitor the magnetic field. The modulated magnetic field can, therefore, be converted into traditional electrical systems (e.g., using current to transfer information). Thus, a communications signal can be converted into a magnetic field and a remote receiver (e.g., a magnetometer) can be used to retrieve the communication from the modulated magnetic field.

[00323] A diamond with a nitrogen vacancy (DNV) can be used to measure a magnetic field. DNV sensors generally have a quick response to magnetic fields, consume little power, and are accurate. Diamonds can be manufactured with nitrogen vacancy (NV) centers in the lattice structure of the diamond. When the NV centers are excited by light, for example green light, and microwave radiation, the NV centers emit light of a different frequency than the excitation light. For example, green light can be used to excite the NV centers, and red light can be emitted from the NV centers. When a magnetic field is applied to the NV centers, the frequency of the light emitted from the NV centers changes. Additionally, when the magnetic field is applied to the NV centers, the frequency of the microwaves at which the NV centers are excited changes. Thus, by shining a green light (or any other suitable color) through a DNV and monitoring the light emitted from the DNV and the frequencies of microwave radiation that excite the NV centers, a magnetic field can be monitored.

[00324] NV centers in a diamond are oriented in one of four spin states. Each spin state can be in a positive direction or a negative direction. The NV centers of one spin state do not respond the same to a magnetic field as the NV centers of another spin state. A magnetic field vector has a magnitude and a direction. Depending upon the direction of the magnetic field at the diamond (and the NV centers), some of the NV centers will be excited by the magnetic field more than others based on the spin state of the NV centers.

[00325] Figs. 32A and 32B are graphs illustrating the frequency response of a DNV sensor in accordance with an illustrative embodiment. Figs. 32A and 32B are meant to be illustrative only and not meant to be limiting. Figs. 32A and 32B plot the frequency of the microwaves applied to a DNV sensor on the x-axis versus the amount of light of a particular frequency (e.g., red) emitted from the diamond. Fig. 32A is the frequency response of the DNV sensor with no magnetic field applied to the diamond, and Fig. 32B is the frequency response of the DNV sensor with a seventy gauss (G) magnetic field applied to the diamond.

[00326] As shown in Fig. 32A, when no magnetic field is applied to the DNV sensor, there are two notches in the frequency response. With no magnetic field applied to the DNV sensor, the spin states are not resolvable. That is, with no magnetic field, the NV centers with various spin states are equally excited and emit light of the same frequency. The two notches shown in Fig. 32A are the result of the positive and negative spin directions. The frequency of the two notches is the axial zero field splitting parameter.

[00327] When a magnetic field is applied to the DNV sensor, the spin states become resolvable in the frequency response. Depending upon the excitation by the magnetic field of NV centers of a particular spin state, the notches corresponding to the positive and negative directions separate on the frequency response graph. As shown in Fig. 32B, when a magnetic field is applied to the DNV sensor, eight notches appear on the graph. The eight notches are four pairs of corresponding notches. For each pair of notches, one notch corresponds to a positive spin state and one notch corresponds to a negative spin state. Each pair of notches corresponds to one of the four spin states of the NV centers. The amount by which the pairs of notches deviate from the axial zero field splitting parameter is dependent upon how strongly the magnetic field excites the NV centers of the corresponding spin states.

[00328] As mentioned above, the magnetic field at a point can be characterized with a magnitude and a direction. By varying the magnitude of the magnetic field, all of the NV centers will be similarly affected. Using the graph of Fig. 32A as an example, the ratio of the distance from 2.87 GHz of one pair to another will remain the same when the magnitude of the magnetic field is altered. As the magnitude is increased, each of the notch pairs will move away from 2.87 GHz at a constant rate, although each pair will move at a different rate than the other pairs.

[00329] When the direction of the magnetic field is altered, however, the pairs of notches do not move in a similar manner to one another. Fig. 33A is a diagram of NV center spin states in accordance with an illustrative embodiment. Fig. 33A conceptually illustrates the four spin states of the NV centers. The spin states are labeled NV A, NV B, NV C, and NV D. Vector 3301 is a representation of a first magnetic field vector with respect to the spin states, and Vector 3302 is a representation of a second magnetic field vector with respect to the spin states. Vector 3301 and vector 3302 have the same magnitude, but differ in direction. Accordingly, based on the change in direction, the various spin states will be affected differently depending upon the direction of the spin states.

[00330] Fig. 33B is a graph illustrating the frequency response of a DNV sensor in response to a changed magnetic field in accordance with an illustrative embodiment. The frequency response graph illustrates the frequency response of the DNV sensor from the magnetic field corresponding to vector 3301 and to vector 3302. As shown in Fig. 33B, the notches corresponding to the NV A and NV D spin states moved closer to the axial zero field splitting parameter from vector 3301 to vector 3302, the negative (e.g., lower frequency notch) notch of the NV C spin state moved away from the axial zero field splitting parameter, the positive (e.g., high frequency notch) of the NV C spin state stayed essentially the same, and the notches corresponding to the NV B spin state increased in frequency (e.g., moved to the right in the graph). Thus, by monitoring the changes in frequency response of the notches, the DNV sensor can determine the direction of the magnetic field.

[00331] Additionally, magnetic fields of different directions can be modulated simultaneously and each of the modulations can be differentiated or identified by the DNV sensor. For example, a magnetic field in the direction of NV A can be modulated with a first pattern, a magnetic field in the direction of NV B can be modulated with a second pattern, a magnetic field in the direction of NV C can be modulated with a third pattern, and a magnetic field in the direction of NV D can be modulated with a fourth pattern. The movement of the notches in the frequency response corresponding to the various spin states can be monitored to determine each of the four patterns.

[00332] However, in some embodiments, the direction of the magnetic field corresponding to the various spin states of a DNV sensor of a receiver may not be known by the transmitter. In such embodiments, by monitoring at least three of the spin states, messages transmitted on two magnetic fields that are orthogonal to one another can be deciphered. Similarly, by monitoring the frequency response of the four spin states, messages transmitted on three magnetic fields that are orthogonal to one another can be deciphered. Thus, in some embodiments, two or three independent signals can be transmitted simultaneously to a receiver that receives and deciphers the two or three signals. Such embodiments can be a multiple-input multiple-output (ΜΙΜΟ) system. Diversity in the polarization of the magnetic field channels provides a full rank channel matrix even through traditionally keyhole channels. In an illustrative embodiment, a full rank channel matrix allows ΜΙΜΟ techniques to leverage all degrees of freedom (e.g., three degrees of polarization). Using a magnetic field to transmit information circumvents the keyhole effect that propagating a radio frequency field can have.

[00333] Fig. 34 is a block diagram of a magnetic communication system in accordance with an illustrative embodiment. An illustrative magnio system 3400 includes input data 3405, a 3410, a transmitter 3445, a modulated magnetic field 3450, a magnetometer 3455, a magnio receiver 3460, and output data 3495. In alternative embodiments, additional, fewer, and/or different elements may be used.

[00334] In an illustrative embodiment, input data 3405 is input into the magnio system 3400, transmitted wirelessly, and the output data 3495 is generated at a location remote from the generation of the input data 3405. In an illustrative embodiment, the input data 3405 and the output data 3495 contain the same information.

[00335] In an illustrative embodiment, input data 3405 is sent to the magnio transmitter 3410. The magnio transmitter 3410 can prepare the information received in the input data 3405 for transmission. For example, the magnio transmitter 3410 can encode or encrypt the information in the input data 3405. The magnio transmitter 3410 can send the information to the transmitter 3445.

[00336] The transmitter 3445 is configured to transmit the information received from the magnio transmitter 3410 via one or more magnetic fields. The transmitter 3445 can be configured to transmit the information on one, two, three, or four magnetic fields. That is, the transmitter 3445 can transmit information via a magnetic field oriented in a first direction, transmit information via a magnetic field oriented in a second direction, transmit information via a magnetic field oriented in a third direction, and/or transmit information via a magnetic field oriented in a fourth direction. In some embodiments in which the transmitter 3445 transmits information via two or three magnetic fields, the magnetic fields can be orthogonal to one another. In alternative embodiments, the magnetic fields are not orthogonal to one another.

[00337] The transmitter 3445 can be any suitable device configured to create a modulated magnetic field. For example, the transmitter 3445 can include one or more coils. Each coil can be a conductor wound around a central axis. For example, in embodiments in which the information is transmitted via three magnetic fields, the transmitter 3445 can include three coils. The central axis of each coil can be orthogonal to the central axis of the other coils.

[00338] The transmitter 3445 generates the modulated magnetic field 3450. The magnetometer 3455 can detect the modulated magnetic field 3450. The magnetometer 3455 can be located remotely from the transmitter 3445. For example, with a current of about ten Amperes through a coil (e.g., the transmitter) and with a magnetometer 3455 with a sensitivity of about one hundred nano-Tesla, a message can be sent, received, and recovered in full with several meters between the transmitter and receiver and with the magnetometer 3455 inside of a Faraday cage. The magnetometer 3455 can be configured to measure the modulated magnetic field 3450 along three or four directions. As discussed above, a magnetometer 3455 using a DNV sensor can measure the magnetic field along four directions associated with four spin states. The magnetometer 3455 can transmit information, such as frequency response information, to the magnio receiver 3460.

[00339] The magnio receiver 3460 can analyze the information received from the magnetometer 3455 and decipher the information in the signals. The magnio receiver 3460 can reconstitute the information contained in the input data 3405 to produce the output data 3495.

[00340] In an illustrative embodiment, the magnio transmitter 3410 includes a data packet generator 3415, an outer encoder 3420, an interleaver 3425, an inner encoder 34340, an interleaver 34345, and an output packet generator 3440. In alternative embodiments, additional, fewer, and/or different elements may be used. The various components of the magnio transmitter 310 are illustrated in Fig. 34 as individual components and are meant to be illustrative only. However, in alternative embodiments, the various components may be combined. Additionally, the use of arrows is not meant to be limiting with respect to the order or flow of operations or information. Any of the components of the magnio transmitter 3410 can be implemented using hardware and/or software.

[00341] The input data 3405 can be sent to the data packet generator 3415. In an illustrative embodiment, the input data 3405 is a series or stream of bits. The data packet generator 3415 can break up the stream of bits into packets of information. The packets can be any suitable size. In an illustrative embodiment, the data packet generator 3415 includes appending a header to the packets that includes transmission management information. In an illustrative embodiment the header can include information used for error detection, such as a checksum. Any suitable header may be used. In some embodiments, the input data 3405 is not broken into packets.

[00342] The stream of data generated by the data packet generator 3415 can be sent to the outer encoder 3420. The outer encoder 3420 can encrypt or encode the stream using any suitable cypher or code. Any suitable type of encryption can be used such as symmetric key encryption. In an illustrative embodiment, the encryption key is stored on memory associated with the magnio transmitter 3410. In an illustrative embodiment, the magnio transmitter 3410 may not include the outer encoder 3420. For example, the messages may not be encrypted. In an illustrative embodiment, the outer encoder 3420 separates the stream into multiple channels. In an illustrative embodiment, the outer encoder outer encoder 3420 performs forward error correction (FEC). In some embodiments, the forward error correction dramatically increases the reliability of transmissions for a given power level.

[00343] In an illustrative embodiment, the encoded stream from the outer encoder 3420 is sent to the interleaver 3425. In an illustrative embodiment, the interleaver 3425 interleaves bits within each packet of the stream of data. In such an embodiment, each packet has the same bits, but the bits are shuffled according to a predetermined pattern. Any suitable interleaving method can be used. In an alternative embodiment, the packets are interleaved. In such an embodiment, the packets are shuffled according to a predetermined pattern. In some embodiments, the magnio transmitter 3410 may not include the interleaver 3425.

[00344] In some embodiments, interleaving data can be used to prevent loss of a sequence of data. For example, if a stream of bits are in sequential order and there is a communication loss during a portion of the stream, there is a relatively large gap in the information corresponding to the lost bits. However, if the bits were interleaved (e.g., shuffled), once the stream is de-interleaved (e.g., unshuffled) at the receiver, the lost bits are not grouped together but are spread across the sequential bits. In some instances, if the lost bits are spread across the message, error correction can be more successful in determining what the lost bits were supposed to be.

[00345] In an illustrative embodiment, the interleaved stream from the interleaver 3425 is sent to the inner encoder 3430. The inner encoder 3430 can encrypt or encode the stream using any suitable cypher or code. Any suitable type of encryption can be used such as symmetric key encryption. In an illustrative embodiment, the encryption key is stored on memory associated with the magnio transmitter 3410. In an illustrative embodiment, the magnio transmitter 3410 may not include the inner encoder 3430. In an illustrative embodiment, the inner encoder 3430 and the outer encoder 3420 perform different functions. For example, the inner encoder 3430 can use a deep convolutional code and can perform most of the forward error correction, and the outer encoder can be used to correct residual errors and can use a different coding technique from the inner encoder 3430 (e.g., a block-parity based encoding technique).

[00346] In an illustrative embodiment, the encoded stream from the inner encoder 3430 is sent to the interleaver 3435. In an illustrative embodiment, the interleaver 3435 interleaves bits within each packet of the stream of data. In such an embodiment, each packet has the same bits, but the bits are shuffled according to a predetermined pattern. Any suitable interleaving method can be used. In an alternative embodiment, the packets are interleaved. In such an embodiments, the packets are shuffled according to a predetermined pattern. In an illustrative embodiment, interleaving the data spreads out burst-like errors across the signal, thereby facilitating the decoding of the message. In some embodiment, the magnio transmitter 3410 may not include the interleaver 3435.

[00347] In an illustrative embodiment, the interleaved stream from the interleaver 3435 is sent to the output packet generator 3440. The output packet generator 3440 can generate the packets that will be transmitted. For example, the output packet generator 3440 may append a header to the packets that includes transmission management information. In an illustrative [00348] In an illustrative embodiment, the output packet generator 3440 appends a synchronization sequence to each of the packets. For example, a synchronization sequence can be added to the beginning of each packet. The packets can be transmitted on multiple channels. In such an embodiment, each channel is associated with a unique synchronization sequence. The synchronization sequence can be used to decipher the channels from one another, as is discussed in greater detail below with regard to the magnio receiver 3460.

[00349] In an illustrative embodiment, the output packet generator 3440 modulates the waveform to be transmitted. Any suitable modulation can be used. In an illustrative embodiment, the waveform is modulated digitally. In some embodiments, minimum shift keying can be used to modulate the waveform. For example, non-differential minimum shift key can be used. In an illustrative embodiment, the waveform has a continuous phase. That is, the waveform does not have phase discontinuities. In an illustrative embodiment, the waveform is sinusoidal in nature.

[00350] In an illustrative embodiment, the modulated waveform is sent to the transmitter 3445. In an illustrative embodiment, multiple modulated waveforms are sent to the transmitter 3445. As mentioned above, two, three, or four signals can be transmitted simultaneously via magnetic fields with different directions. In an illustrative embodiment, three modulated waveforms are sent to the transmitter 3445. Each of the waveforms can be used to modulate a magnetic field, and each of the magnetic fields can be orthogonal to one another.

[00351] The transmitter 3445 can use the received waveforms to produce the modulated magnetic field 3450. The modulated magnetic field 3450 can be a combination of multiple magnetic fields of different directions. The frequency used to modulate the modulated magnetic field 3450 can be any suitable frequency. In an illustrative embodiment, the carrier frequency of the modulated magnetic field 3450 can be 10 kHz. In alternative embodiments, the carrier frequency of the modulated magnetic field 3450 can be less than or greater than 10 kHz. In some embodiments, the carrier frequency can be modulated to plus or minus the carrier frequency. That is, using the example in which the carrier frequency is 10 kHz, the carrier frequency can be modulated down to 0 Hz and up to 20 kHz. In alternative embodiments, any suitable frequency band can be used.

[00352] Figs. 35 A and 35B show the strength of a magnetic field versus frequency in accordance with an illustrative embodiment. Figs. 35A and 35B are meant to be illustrative only and not meant to be limiting. In some instances, the magnetic spectrum is relatively noisy. As shown in Fig. 35 A, the noise over a large band (e.g., 0-200 kHz) is relatively high. Thus, communicating over such a large band may be difficult. Fig. 35B illustrates the noise over a smaller band (e.g., 1-3 kHz). As shown in Fig. 35B, the noise over a smaller band is relatively low. Thus, modulating the magnetic field across a smaller band of frequencies can be less noisy and more effective. In an illustrative embodiment, the magnio transmitter 3410 can monitor the magnetic field and determine a suitable frequency to modulate the magnetic fields to reduce noise. That is, the magnio transmitter 3410 can find a frequency that has a high signal to noise ratio. In an illustrative embodiment, the magnio transmitter 3410 determines a frequency band that has noise that is below a predetermined threshold.

[00353] In an illustrative embodiment, the magnio receiver 3460 includes the demodulator 3465, the de-interleaver 3470, the soft inner decoder 3475, the de-interleaver 3480, the outer decoder 3485, and the output data generator 3490. In alternative embodiments, additional, fewer, and/or different elements may be used. For example, the magnio receiver 3460 can include the magnetometer 3455 in some embodiments. The various components of the magnio receiver 3460 are illustrated in Fig. 34 as individual components and are meant to be illustrative only. However, in alternative embodiments, the various components may be combined. Additionally, the use of arrows is not meant to be limiting with respect to the order or flow of operations or information. Any of the components of the magnio receiver 3460 can be implemented using hardware and/or software.

[00354] The magnetometer 3455 is configured to measure the modulated magnetic field 3450. In an illustrative embodiment, the magnetometer 3455 includes a DNV sensor. The magnetometer 3455 can monitor the modulated magnetic field 3450 in up to four directions. As illustrated in Fig. 2A, the magnetometer 3455 can be configured to measure the magnetometer 3455 in one or more of four directions that are tetrahedronally arranged. As mentioned above, the magnetometer 3455 can monitor n + 1 directions where n is the number of channels that the transmitter 3445 transmits on. For example, the transmitter 3445 can transmit on three channels, and the magnetometer 3455 can monitor four directions. In an alternative embodiment, the transmitter 3445 can transmit via the same number of channels (e.g., four) as directions that the magnetometer 3455 monitors.

[00355] The magnetometer 3455 can send information regarding the modulated magnetic field 3450 to the demodulator 3465. The demodulator 3465 can analyze the received information and determine the direction of the magnetic fields that were used to create the modulated magnetic field 3450. That is, the demodulator 3465 can determine the directions of the channels that the transmitter 3445 transmitted on. As mentioned above, the transmitter 3445 can transmit multiple streams of data, and each stream of data is transmitted on one channel.

Each of the streams of data can be preceded by a unique synchronization sequence. In an illustrative embodiment, the synchronization sequence includes 1023 bits. In alternative embodiments, the synchronization sequence includes more than or fewer than 1023 bits. Each of the streams can be transmitted simultaneously such that each of the channels are time-aligned with one another. The demodulator 3465 can monitor the magnetic field in multiple directions simultaneously. Based on the synchronization sequence, which is known to the magnio receiver 3460, the demodulator 3465 can determine the directions corresponding to the channels of the transmitter 3445. When the streams of synchronization sequences are time-aligned, the demodulator 3465 can monitor the modulated magnetic field 3450 to determine how the multiple channels mixed. Once the demodulator 3465 determines how the various channels are mixed, the channels can be demodulated.

[00356] For example, the transmitter 3445 transmits on three channels, with each channel corresponding to an orthogonal direction. Each channel is used to transmit a stream of information. For purposes of the example, the channels are named "channel A," "channel B," and "channel C." The magnetometer 3455 monitors the modulated magnetic field 3450 in four directions. The demodulator 3465 can monitor for three signals in orthogonal directions. For purposes of the example, the signals can be named "signal 1," "signal 2," and "signal 3." Each of the signals can contain a unique, predetermined synchronization sequence. The demodulator 3465 can monitor the modulated magnetic field 3450 for the signals to be transmitted on the channels. There is a finite number of possible combinations that the signals can be received at the magnetometer 3455. For example, signal 1 can be transmitted in a direction corresponding to channel A, signal 2 can be transmitted in a direction corresponding to channel B, and signal 3 can be transmitted in a direction corresponding to channel C. In another example, signal 2 can be transmitted in a direction corresponding to channel A, signal 3 can be transmitted in a direction corresponding to channel B, and signal 1 can be transmitted in a direction corresponding to channel C, etc. The modulated magnetic field 3450 of the synchronization sequence for each of the possible combinations that the signals can be received at the magnetometer 3455 can be known by the demodulator 3465. The demodulator 3465 can monitor the output of the magnetometer 3455 for each of the possible combinations. Thus, when one of the possible combinations is recognized by the demodulator 3465, the demodulator 3465 can monitor for additional data in directions associated with the recognized combination. In another example, the transmitter 3445 transmits on two channels, and the magnetometer 3455 monitors the modulated magnetic field 3450 in three directions.

[00357] The demodulated signals (e.g., the received streams of data from each of the channels) is sent to the de-interleaver 3470. The de-interleaver 3470 can undo the interleaving of the interleaver 3435. The de-interleaved streams of data can be sent to the soft inner decoder 3475, which can undo the encoding of the inner encoder 3430. Any suitable decoding method can be used. For example, in an illustrative embodiment the inner encoder 3430 uses a threeway, soft-decision turbo decoding function. In an alternative embodiment, a two-way, soft-decision turbo decoding function may be used. For example, the expected cluster positions for signal levels are learned by the magnio receiver 3460 during the synchronization portion of the transmission. When the payload/data portion of the transmission is processed by the magnio receiver 3460, distances from all possible signal clusters to the observed signal value are computed for every bit position. The bits in each bit position are determined by combining the [00358] The decoded stream can be transmitted to the de-interleaver 3480. The deinterleaver 3480 can undo the interleaving of the interleaver 3425. The de-interleaved stream can be sent to the outer decoder 3485. In an illustrative embodiment, the outer decoder 3485 undoes the encoding of the outer encoder 3420. The unencoded stream of information can be sent to the output data generator 3490. In an illustrative embodiment, the output data generator 3490 undoes the packet generation of data packet generator 3415 to produce the output data 3495.

[00359] Fig. 36 is a block diagram of a computing device in accordance with an illustrative embodiment. An illustrative computing device 3600 includes a memory 3610, a processor 3605, a transceiver 3615, a user interface 3620, and a power source 3625. In alternative embodiments, additional, fewer, and/or different elements may be used. The computing device 3600 can be any suitable device described herein. For example, the computing device 3600 can be a desktop computer, a laptop computer, a smartphone, a specialized computing device, etc. The computing device 3600 can be used to implement one or more of the methods described herein.

[00360] In an illustrative embodiment, the memory 3610 is an electronic holding place or storage for information so that the information can be accessed by the processor 3605. The memory 3610 can include, but is not limited to, any type of random access memory (RAM), any type of read only memory (ROM), any type of flash memory, etc. such as magnetic storage devices (e.g., hard disk, floppy disk, magnetic strips, etc.), optical disks (e.g., compact disk (CD), digital versatile disk (DVD), etc.), smart cards, flash memory devices, etc. The computing device 3600 may have one or more computer-readable media that use the same or a different memory media technology. The computing device 3600 may have one or more drives that support the loading of a memory medium such as a CD, a DVD, a flash memory card, etc.

[00361] In an illustrative embodiment, the processor 3605 executes instructions. The instructions may be carried out by a special purpose computer, logic circuits, or hardware circuits. The processor 3605 may be implemented in hardware, firmware, software, or any combination thereof. The term "execution" is, for example, the process of running an application or the carrying out of the operation called for by an instruction. The instructions may be written using one or more programming language, scripting language, assembly language, etc. The processor 3605 executes an instruction, meaning that it performs the operations called for by that instruction. The processor 3605 operably couples with the user interface 3620, the transceiver 3615, the memory 3610, etc. to receive, to send, and to process information and to control the operations of the computing device 3600. The processor 3605 may retrieve a set of instructions from a permanent memory device such as a ROM device and copy the instructions in an executable form to a temporary memory device that is generally some form of RAM. An illustrative computing device 3600 may include a plurality of processors that use the same or a different processing technology. In an illustrative embodiment, the instructions may be stored in memory 3610.

[00362] In an illustrative embodiment, the transceiver 3615 is configured to receive and/or transmit information. In some embodiments, the transceiver 3615 communicates information via a wired connection, such as an Ethernet connection, one or more twisted pair wires, coaxial cables, fiber optic cables, etc. In some embodiments, the transceiver 3615 communicates information via a wireless connection using microwaves, infrared waves, radio waves, spread spectrum technologies, satellites, etc. The transceiver 3615 can be configured to communicate with another device using cellular networks, local area networks, wide area networks, the Internet, etc. In some embodiments, one or more of the elements of the computing device 3600 communicate via wired or wireless communications. In some embodiments, the transceiver 3615 provides an interface for presenting information from the computing device 3600 to external systems, users, or memory. For example, the transceiver 3615 may include an interface to a display, a printer, a speaker, etc. In an illustrative embodiment, the transceiver 3615 may also include alarm/indicator lights, a network interface, a disk drive, a computer memory device, etc. In an illustrative embodiment, the transceiver 3615 can receive information from external systems, users, memory, etc.

[00363] In an illustrative embodiment, the user interface 3620 is configured to receive and/or provide information from/to a user. The user interface 3620 can be any suitable user interface. The user interface 3620 can be an interface for receiving user input and/or machine instructions for entry into the computing device 3600. The user interface 3620 may use various input technologies including, but not limited to, a keyboard, a stylus and/or touch screen, a mouse, a track ball, a keypad, a microphone, voice recognition, motion recognition, disk drives, remote controllers, input ports, one or more buttons, dials, joysticks, etc. to allow an external source, such as a user, to enter information into the computing device 3600. The user interface 3620 can be used to navigate menus, adjust options, adjust settings, adjust display, etc.

[00364] The user interface 3620 can be configured to provide an interface for presenting information from the computing device 3600 to external systems, users, memory, etc. For example, the user interface 3620 can include an interface for a display, a printer, a speaker, alarm/indicator lights, a network interface, a disk drive, a computer memory device, etc. The user interface 3620 can include a color display, a cathode-ray tube (CRT), a liquid crystal display (LCD), a plasma display, an organic light-emitting diode (OLED) display, etc.

[00365] In an illustrative embodiment, the power source 36236 is configured to provide electrical power to one or more elements of the computing device 3600. In some embodiments, the power source 3625 includes an alternating power source, such as available line voltage (e.g., 120 Volts alternating current at 60 Hertz in the United States). The power source 3625 can include one or more transformers, rectifiers, etc. to convert electrical power into power useable by the one or more elements of the computing device 3600, such as 1.5 Volts, 8 Volts, 12 Volts, 24 Volts, etc. The power source 3625 can include one or more batteries.

[00366] METHOD FOR RESOLVING NATURAL SENSOR AMBIGUITY FOR DNV DIRECTION FINDING APPLICATIONS

[00367] Natural ambiguity of NV center magnetic sensor system [00368] The NV center magnetic sensor that operates as described above is capable of resolving a magnetic field to an unsigned vector. As shown in FIG. 37, due to the symmetry of the peaks for the ms = -1 and the ms = +1 spin states around the zero splitting photon energy the structure of the DNV material produces a measured fluorescence spectrum as a function of RF frequency that is the same for a positive and a negative magnetic field acting on the DNV material. The symmetry of the fluorescence spectra makes the assignment of a sign to the calculated magnetic field vector unreliable. The natural ambiguity introduced to the magnetic field sensor is undesirable in some applications, such as magnetic field based direction sensing.

[00369] In some circumstances, real world conditions allow the intelligent assignment of a sign to the unsigned magnetic field vector determined from the fluorescence spectra described above. If a known bias field is used that is much larger than the signal of interest, the sign of the magnetic field vector may be determine by whether the total magnetic field, cumulative of the bias field and the signal of interest, increases or decreases. If the magnetic sensor is employed to detect submarines from a surface ship, assigning the calculated magnetic field vector a sign that would place a detected submarine above the surface ship would be nonsensical. Alternatively, where the sign of the vector is not important a sign can be arbitrarily assigned to the unsigned vector.

[00370] It is possible to unambiguously determine a magnetic field vector with a DNV magnetic field sensor. The method of determining the signed magnetic field vector may be performed with a DNV magnetic field sensor of the type shown in FIG. 6 and described above.

In general, the recovery of the vector may be achieved as described in co-pending U.S.

Application No. _/_, filed January 21, 2016, titled “APPARATUS AND METHOD FOR RECOVERY OF THREE DIMENSIONAL MAGNETIC FIELD FROM A MAGNETIC DETECTION SYSTEM”, which is incorporated by reference herein in its entirety.

[00371] As shown in FIG. 2, the energy levels of the ms = -1 and the ms = +1 spin states are different. For this reason, the relaxation times from the excited triplet states (3E) to the excited intermediate singlet state (A) for electrons with the ms = -1 and the ms = +1 spin states are not the same. The difference in relaxation times for electrons of ms = -1 and the ms = +1 spin states is on the order of picoseconds or nanoseconds. It is possible to measure the difference in relaxation times for the electrons with the ms = -1 and the ms = +1 spin states by utilizing pulsed RF excitation such that the inequality in the relaxation times accumulates over a large number of electron cycles, producing a difference in observed relaxation times on the order of microseconds.

[00372] As described above, the application of RF excitation to the DNV material produces a decrease in fluorescence intensity at the resonant RF frequencies for the ms = -1 and the ms = +1 spin states. For this reason, at RF frequencies that excite electrons to the ms = -1 and the ms = +1 spin states, an equilibrium fluorescence intensity will be lower than the equilibrium fluorescence intensity in the absence of the applied RF excitation. The time it takes to transition from the equilibrium fluorescence intensity in the absence of RF excitation to the equilibrium fluorescence intensity with the application of RF excitation may be employed to calculate an “equilibration time.” [00373] An “equilibration time” as utilized herein refers to the time between the start of an RF excitation pulse and when a predetermined percentage of the equilibrium fluorescence intensity is achieved. The predetermined amount of the equilibrium fluorescence at which the equilibration time is calculated may be about 20% to about 80% of the equilibrium fluorescence, such as about 30%, 40%, 50%, 60%, or 70% of the equilibrium fluorescence. The equilibration time as shown in FIGS. 38, 40 and 41 is actually a decay time, as the fluorescence intensity is actually decreasing in the presence of the RF excitation, but has been inverted for the sake of clarity.

[00374] A shown in FIG. 38, the fluorescence intensity of the DNV material varies with the application of a pulsed RF excitation source. When the RF pulse is in the “on” state, the electrons decay through a non-fluorescent path and a relatively dark equilibrium fluorescence is achieved. The absence of the RF excitation, when the pulse is in the “off’ state, results in a relatively bright equilibrium fluorescence. The transition between the two fluorescence equilibrium states is not instantaneous, and the measurement of the equilibration time at a predetermined value of fluorescence intensity provides a repeatable indication of the relaxation time for the electrons at the RF excitation frequency.

[00375] The difference in the relaxation time between the electrons of the ms = -1 and the ms = +1 spin states may be measured due to the different RF excitation resonant frequencies for each spin state. As shown in FIG. 39, a fluorescence intensity spectra of the DNV material measured as a function of RF excitation frequency includes four Lorentzian pairs, one pair for each crystallographic plane of the DNV material. The peaks in a Lorentzian pair correspond to a ms = -1 and a ms = +1 spin state. By evaluating the equilibration time for each peak in a Lorentzian pair, the peak which corresponds to the higher energy state may be identified. The higher energy peak provides a reliable indication of the sign of the magnetic field vector.

[00376] The Lorentzian pair of the fluorescence spectra which are located furthest from the zero splitting energy may be selected to calculate the equilibration time. These peaks include the least signal interference and noise, allowing a more reliable measurement. The preferred Lorentzian pair is boxed in FIG. 39.

[00377] A plot of the fluorescence intensity for a single RF pulse as a function of time is shown in FIG. 40. The frequency of the pulsed RF excitation is selected to be the maximum value for each peak in the Lorentzian pair. The other conditions for the measurement of an equilibration time for each peak in the Lorentzian pair are held constant. As shown in FIG. 41, the peaks of the Lorentzian pair have an equilibration time when calculated to 60% of the equilibrium intensity value that is distinguishable. The RF pulse duration may be set such that the desired percentage of the equilibrium fluorescence intensity is achieved for each “on” portion of the pulse, and the full “bright” equilibrium intensity is achieved during the “off’ portion of the pulse.

[00378] The equilibrium fluorescence intensity under the application of the RF excitation may be set by any appropriate method. According to some embodiments, the RF excitation may be maintained until the intensity becomes constant, and the constant intensity may be considered the equilibrium intensity value utilized to calculate the equilibration time. Alternatively, the equilibrium intensity may be set to the intensity at the end of an RF excitation pulse. According to other embodiments, a decay constant may be calculated based on the measured fluorescence intensity and a theoretical data fit employed to determine the equilibrium intensity value.

[00379] The peak in the Lorentzian pair that exhibits the higher measured equilibration time is associated with the higher energy level electron spin state. For this reason, the peak of the

Lorentzian pair with the longer equilibration time is assigned the ms = +1 spin state, and the other peak in the Lorentzian pair is assigned the ms = -1 spin state. The signs of the peaks in the other Lorentzian pairs in the fluorescence spectra of the DNV material as a function of RF frequency may then be assigned, and the signed magnetic field vector calculated.

[00380] To demonstrate that the equilibration time of each peak in a Lorentzian pair does indeed vary with magnetic field direction, the equilibration time for a single peak in a Lorentzian pair was measured under both a positive and a negative magnetic bias field which were otherwise equivalent. As shown in FIG. 42, a real and measurable difference in equilibration time was observed between the opposite bias fields.

[00381] The method of determining a sign of a magnetic field vector with a DNV magnetic sensor described herein may be performed with the DNV magnetic field sensor shown in FIG. 6. No additional hardware is required.

[00382] The controller of the magnetic field sensor may be programmed to determine the location of peaks in a fluorescence spectra of a DNV material as a function of RF frequency. The equilibration time for the peaks of a Lorentzian pair located the furthest from the zero field energy may then be calculated. The controller may be programmed to provide a pulsed RF excitation energy by controlling a RF excitation source and also control an optical excitation source to excite the DNV material with continuous wave optical excitation. The resulting optical signal received at the optical detector may be analyzed by the controller to determine the equilibration time associated with each peak in the manner described above. The controller may be programmed to assign a sign to each peak based on the measured equilibration time. The peak with the greater measured equilibration time may be assigned the ms = +1 spin state.

[00383] The method of assigning a sign to a magnetic field vector described above may also be applied to magnetic field sensors based on magneto-optical defect center materials other than DNV.

[00384] The DNV magnetic field sensor described herein that produces a signed magnetic field vector may be especially useful in applications in which the direction of a measured

[00385] HYDROPHONE

[00386] FIGS. 43 A and 43B are diagrams illustrating hydrophone systems in accordance with illustrative embodiments. An illustrative system 4300 includes a hull 4305 and a magnetometer 4310. In alternative embodiments, additional, fewer, or different elements can be used. For example, an acoustic transmitter can be used to generate one or more acoustic signals. In the embodiments in which a transmitter is not used, the system 4300 can be used as a passive sonar system. For example, the system 4300 can be used to detect sounds created by something other than a transmitter (e.g., a ship, a boat, an engine, a mammal, ice movement, etc.).

[00387] In an illustrative embodiment, the hull 4305 is the hull of a vessel such as a ship or a boat. The hull 4305 can be any suitable material, such as steel or painted steel. In alternative embodiments, the magnetometer 4310 is installed in alternative structures such as a bulk head or a buoy.

[00388] As illustrated in FIG. 43A, the magnetometer 4310 can be located within the 4305. In the embodiment, the magnetometer 4310 is located at the outer surface of the hull 4305. In alternative embodiments, the magnetometer 4310 can be located at any suitable location. For example, magnetometer 4310 can be located near the middle of the hull 4305, at an inner surface of the hull 4305, or on an inner or outer surface of the hull 4305.

[00389] In an illustrative embodiment, the magnetometer 4310 is a magnetometer with a diamond with NV centers. In an illustrative embodiment, the magnetometer 4310 has a sensitivity of about 0.1 micro Tesla. In alternative embodiments, the magnetometer 4310 has a sensitivity of greater than or less than 0.1 micro Tesla.

[00390] In the embodiment illustrated in FIG. 43 A, sound waves 4315 propagate through a fluid with dissolved ions, such as sea water. As the sound waves 4315 move the ions in the fluid, the ions create a magnetic field. For example, as the ions move within the magnetic field of the Earth, the ions create a magnetic field that is detectable by the magnetometer 4310. In another embodiment, a magnetic field source such as a permanent magnet or an electromagnet can be used. The movement of the ions with respect to the source of the magnetic field (e.g., the Earth) creates the magnetic field detectable by the magnetometer 4310.

[00391] In an illustrative embodiment, the sound waves 4315 travel through sea water. The density of dissolved ions in the fluid near the magnetometer 4310 depends on the location in the sea that the magnetometer 4310 is. For example, some locations have a lower density of dissolved ions than others. The higher the density of the dissolved ions, the greater the combined magnetic field created by the movement of the ions. In an illustrative embodiment, the strength of the combined magnetic field can be used to determine the density of the dissolved ions (e.g., the salinity of the sea water).

[00392] In an illustrative embodiment, the hull 4305 is the hull of a ship that travels through the sea water. As noted above, the movement of the ions relative to the source magnetic field can be measured by the magnetometer 4310. Thus, the magnetometer 4310 can be used to detect and measure the sound waves 4315 as the magnetometer 4310 moves through the sea water and as the magnetometer 4310 is stationary in the sea water.

[00393] In an illustrative embodiment, the magnetometer 4310 can measure the magnetic field caused by the moving ions in any suitable direction. For example, the magnetometer 4310 can measure the magnetic field caused by the movement of the ions when the sound waves 4315 is perpendicular to the hull 4305 or any other suitable angle. In some embodiments, the magnetometer 4310 measures the magnetic field caused by the movement of ions caused by sound waves 4315 that are parallel to the surface of the hull 4305.

[00394] An illustrative system 4350 includes the hull 4305 and an array of magnetometers 4355. In alternative embodiments, additional, fewer, and/or different elements can be used. For example, although FIG. 43B illustrates four magnetometers 4355 are used. In alternative embodiments, the system 4350 can include fewer than four magnetometers 4355 or more than magnetometers 4355. The array of the magnetometers 4355 can be used to increase the sensitivity of the hydrophone. For example, by using multiple magnetometers 4355, the hydrophone has multiple measurement points.

[00395] The array of magnetometers 4355 can be arranged in any suitable manner. For example, the magnetometers 4355 can be arranged in a line. In another example, the magnetometers 4355 can be arranged in a circle, in concentric circles, in a grid, etc. The array of magnetometers 4355 can be uniformly arranged (e.g., the same distance from one another) or non-uniformly arranged. The array of magnetometers 4355 can be used to determine the direction from which the sound waves 4315 travel. For example, the sound waves 4315 can cause ions near one the bottom magnetometer of the magnetometers 4355 of the embodiment illustrated in the system 4350 to create a magnetic field before the sound waves 4315 cause ions near the top magnetometer of the magnetometers 4355. Thus, it can be determined that the sound waves 4315 travels from the bottom to the top of FIG. 43B.

[00396] In an illustrative embodiment, the magnetometer 4310 or the magnetometers 4355 can determine the angle that the sound waves 4315 travel relative to the magnetometer 4310 based on the direction of the magnetic field caused by the movement of the ions. For example, individual magnetometers of the magnetometers 4355 can each be configured to measure the magnetic field of the ions in a different direction. Principles of beamforming can be used to determine the direction of the magnetic field. In alternative embodiments, any suitable magnetometer 4310 or magnetometers 4355 can be used to determine the direction of the magnetic field and/or the direction of the acoustic signal.

[00397] MAGNETIC NAVIGATION METHODS AND SYSTEMS UTILIZING POWER GRID AND COMMUNICATION NETWORK

[00398] In some embodiments, methods and configurations are disclosed for diamond nitrogen-vacancy (DNV) magnetic navigation via power transmission and distribution lines. The characteristic magnetic signature of human infrastructure provides context for navigation. For example, power lines, which have characteristic magnetic signatures, can serve as roads and highways for mobile platforms (e.g., UASs). Travel in relatively close proximity to power lines may allow stealthy transit, may provide the potential for powering the mobile platform itself, and may permit point-to-point navigation both over long distances and local routes.

[00399] Some implementations can include one or more magnetic sensors, a magnetic navigation database, and a feedback loop that controls the UAS position and orientation. DNV magnetic sensors and related systems and methods may provide high sensitivity magnetic field measurements. The DNV magnetic systems and methods can also be low cost, space, weight, and power (C-SWAP) and benefit from a fast settling time. The DNV magnetic field measurements may allow UAS systems to align themselves with the power lines, and to rapidly move along the power-line infrastructure routes. The subject solution can enable navigation in poor visibility conditions and/or in GPS-denied environments. Such magnetic navigation allows for UAS operation in close proximity to power lines facilitating stealthy transit. DNV-based magnetic systems and methods can be approximately 100 times smaller than conventional systems and can have a reaction time that that is approximately 100,000 times faster than other systems.

[00400] FIG. 44 is a diagram illustrating an example of UAS 4402 navigation along power lines 4404, 4406, and 4408, according to some implementations of the subject technology. The UAS 4402 can exploit the distinct magnetic signatures of power lines for navigation such that the power lines can serve as roads and highways for the UAS 4402 without the need for detailed a priori knowledge of the route magnetic characteristics. As shown in FIG. 45A, a ratio of signal strength of two magnetic sensors, A and B (4410 and 4412 in Figure 44), attached to wings of the UAS 4402, varies as a function of distance, x, from a center line of an example three-line power transmission line structure 4404, 4406, and 4408. When the ratio is near 1, point 4522, the UAS 4402 is centered over the power transmission line structure, x=0 at point 4520.

[00401] A composite magnetic field (B-field) 4506 from all (3) wires shown in Figure 45B. This field is an illustration of the strength of the magnetic field measured by one or more magnetic sensors in the UAS. In this example, the peak of the field 4508 corresponds to the UAS 4402 being above the location of the middle line 4406. When the UAS 4402 has two magnetic sensors, the sensors would read strengths corresponding to points 4502 and 4504. A computing system on the UAS or remote from the UAS, can calculate combined readings. Not all of the depicted components may be required, however, and one or more implementations may include additional components not shown in the figure. Variations in the arrangement and type [00402] As an example of some implementations, a vehicle, such as a UAS, can include one or more navigation sensors, such as DNV sensors. The vehicle's mission could be to travel to an initial destination and possibly return to a final destination. Known navigation systems can be used to navigate the vehicle to an intermediate location. For example, a UAS can fly using GPS and/or human controlled navigation to the intermediate location. The UAS can then begin looking for the magnetic signature of a power source, such as power lines. To find a power line, the UAS can continually take measurements using the DNV sensors. The UAS can fly in a circle, straight line, curved pattern, etc. and monitor the recorded magnetic field. The magnetic field can be compared to known characteristics of power lines to identify if a power line is in the vicinity of the UAS. For example, the measured magnetic field can be compared with known magnetic field characteristics of power lines to identify the power line that is generating the measured magnetic field. In addition, information regarding the electrical infrastructure can be used in combination with the measured magnetic field to identify the current source. For example, a database regarding magnetic measurements from the area that were previously taken and recorded can be used to compare the current readings to help determine the UAS's location.

[00403] In some implementations, once the UAS identifies a power line the UAS positions itself at a known elevation and position relative to the power line. For example, as the UAS flies over a power line, the magnetic field will reach a maximum value and then begin to decrease as the UAS moves away from the power line. After one sweep of a known distance, the UAS can return to where the magnetic field was the strongest. Based upon known characteristics of power lines and the magnetic readings, the UAS can determine the type of power line.

[00404] Once the current source has been identified, the UAS can change its elevation until the magnetic field is a known value that corresponds with an elevation above the identified power line. For example, as shown in Figure 6, a magnetic field strength can be used to determine an elevation above the current source. The UAS can also use the measured magnetic field to position itself offset from directly above the power line. For example, once the UAS is positioned above the current source, the UAS can move laterally to an offset position from the current source. For example, the UAS can move to be 10 kilometers to the left or right of the current source.

[00405] The UAS can be programmed, via a computer 306, with a flight path. In some implementations, once the UAS establishes its position, the UAS can use a flight path to reach its destination. In some implementations, the magnetic field generated by the transmission line is perpendicular to the transmission line. In some implementations, the vehicle will fly perpendicular to the detected magnetic field. In one example, the UAS can follow the detected power line to its destination. In this example, the UAS will attempt to keep the detected magnetic field to be close to the original magnetic field value. To do this, the UAS can change elevation or move laterally to stay in its position relative to the power line. For example, a power line that is rising in elevation would cause the detected magnetic field to increase in strength as the distance between the UAS and power line decreased. The navigation system of the UAS can detect this increased magnetic strength and increase the elevation of the UAS. In addition, on board instruments can provide an indication of the elevation of the UAS. The navigation system can also move the UAS laterally to the keep the UAS in the proper position relative to the power lines.

[00406] The magnetic field can become weaker or stronger, as the UAS drifts from its position of the transmission line. As the change in the magnetic field is detected, the navigation system can make the appropriate correction. For a UAS that only has a single DNV sensor, when the magnetic field had decreased by more than a predetermined amount the navigation system can make corrections. For example, the UAS can have an error budget such that the UAS will attempt to correct its course if the measured error is greater than the error budget. If the magnetic field has decreased, the navigation system can instruct the UAS to move to the left.

The navigation system can continually monitor the magnetic field to see if moving to the left corrected the error. If the magnetic field further decreased, the navigation system can instruct the UAS to fly to the right to its original position relative to the current source and then move further to the right. If the magnetic field decreased in strength, the navigation system can deduce that the UAS needs to decrease its altitude to increase the magnetic field. In this example, the UAS would originally be flying directly over the current source, but the distance between the current source and the UAS has increased due to the current source being at a lower elevation. Using this feedback loop of the magnetic field, the navigation system can keep the UAS centered or at an offset of the current source. The same analysis can be done when the magnetic field increases in strength. The navigation can maneuver until the measured magnetic field is within the proper range such that the UAS in within the flight path.

[00407] The UAS can also use the vector measurements from one or more DNV sensors to determine course corrections. The readings from the DNV sensor are vectors that indicate the direction of the sensed magnetic field. Once the UAS knows the location of the power line, as the magnitude of the sensed magnetic field decreases, the vector can provide an indication of the direction the UAS should move to correct its course. For example, the strength of the magnetic field can be reduced by a threshold amount from its ideal location. The magnetic vector of this field can be used to indicate the direction the UAS should correct to increase the strength of the magnetic field. In other words, the magnetic field indicates the direction of the field and the UAS can use this direction to determine the correct direction needed to increase the strength of the magnetic field, which could correct the UAS flight path to be back over the transmission wire.

[00408] Using multiple sensors on a single vehicle can reduce the amount of maneuvering that is needed or eliminate the maneuvering all together. Using the measured magnetic field from each of the multiple sensors, the navigation system can determine if the UAS needs to correct its course by moving left, right, up, or down. For example, if both DNV sensors are reading a stronger field, the navigation system can direct the UAS to increase its altitude. As another example if the left sensor is stronger than expected but the right sensor is weaker than expected, the navigation system can move the UAS to the left.

[00409] In addition to the current readings from the one or more sensors, a recent history of readings can also be used by the navigation system to identify how to correct the UAS course.

For example, if the right sensor had a brief increase in strength and then a decrease, while the left [00410] FIG. 46 illustrates a high-level block diagram of an example UAS navigation system 4600, according to some implementations of the subject technology. In some implementations, the UAS navigation system of the subject technology includes a number of DNV sensors 4602a, 4602b, and 4602c, a navigation database 4604, and a feedback loop that controls the UAS position and orientation. In other implementations, a vehicle can contain a navigation control that is used to navigate the vehicle. For example, the navigation control can change the vehicle's direction, elevation, speed, etc. The DNV magnetic sensors 4602a-4602c have high sensitivity to magnetic fields, low C-SWAP and a fast settling time. The DNV magnetic field measurements allow the UAS to align itself with the power lines, via its characteristic magnetic field signature, and to rapidly move along power-line routes. Not all of the depicted components may be required, however, and one or more implementations may include additional components not shown in the figure. Variations in the arrangement and type of the components may be made, and additional components, different components, or fewer components may be provided.

[00411] FIG. 47 illustrates an example of a power line infrastructure. It is known that widespread power line infrastructures, such as shown in FIG. 47, connect cities, critical power system elements, homes and businesses. The infrastructure may include overhead and buried power distribution lines, transmission lines, railway catenary and 3rd rail power lines and underwater cables. Each element has a unique electro-magnetic and spatial signature. It is understood that, unlike electric fields, the magnetic signature is minimally impacted by manmade structures and electrical shielding. It is understood that specific elements of the infrastructure will have distinct magnetic and spatial signatures and that discontinuities, cable droop, power consumption and other factors will create variations in magnetic signatures that can also be leveraged for navigation.

[00412] Figures 48A and 48B illustrate examples of magnetic field distribution for overhead power lines and underground power cables. Both above-ground and buried power cables emit magnetic fields, which unlike electrical fields are not easily blocked or shielded. Natural Earth and other man-made magnetic field sources can provide rough values of absolute location. However, the sensitive magnetic sensors described here can locate strong man-made magnetic sources, such as power lines, at substantial distances. As the UAS moves, the measurements can be used to reveal the spatial structure of the magnetic source (point source, line source, etc.) and thus identify the power line as such. In addition, once detected the UAS can guide itself to the power line via its magnetic strength. Once the power line is located its structure is determined, and the power line route is followed and its characteristics are compared to magnetic way points to determine absolute location. Fixed power lines can provide precision location reference as the location and relative position of poles and towers are known. A compact on-board database can provide reference signatures and location data for waypoints. Not all of the depicted components may be required, however, and one or more implementations may include additional components not shown in the figure. Variations in the arrangement and type of the components may be made, and additional components, different components, or fewer components may be provided.

[00413] Figure 49 illustrates examples of magnetic field strength of power lines as a function of distance from the centerline showing that even low current distribution lines can be detected to distances in excess of 10 km. Here it is understood that DNV sensors provide 0.01 uT sensitivity (le-10 T), and modeling results indicates that high current transmission line (e.g. with 1000 A - 4000 A) can be detected over many tens of km. These strong magnetic sources allow the UAS to guide itself to the power lines where it can then align itself using localized relative field strength and the characteristic patterns of the power-line configuration as described below.

[00414] Figure 50 illustrates an example of a UAS 5002 equipped with DNV sensors 5004 and 5006. Figure 51 is a plot of a measured differential magnetic field sensed by the DNV sensors when in close proximity of the power lines. While power line detection can be performed with only a single DNV sensor precision alignment for complex wire configurations can be achieved using multiple arrayed sensors. For example, the differential signal can eliminate the influence of diurnal and seasonal variations in field strength. Not all of the depicted components may be required, however, and one or more implementations may include additional components not shown in the figure. Variations in the arrangement and type of the components may be made, and additional components, different components, or fewer components may be provided.

[00415] In various other implementations, a vehicle can also be used to inspect power transmission lines, power lines, and power utility equipment. For example, a vehicle can include one or more magnetic sensors, a magnetic waypoint database, and an interface to UAS flight control. The subject technology may leverage high sensitivity to magnetic fields of DNV magnetic sensors for magnetic field measurements. The DNV magnetic sensor can also be low cost, space, weight, and power (C-SWAP) and benefit from a fast settling time. The DNV magnetic field measurements allow UASs to align themselves with the power lines, and to rapidly move along power-line routes and navigate in poor visibility conditions and/or in GPS-denied environments. It is understood that DNV-based magnetic sensors are approximately 100 times smaller than conventional magnetic sensors and have a reaction time that that is approximately 100,000 times faster than sensors with similar sensitivity such as the EMDEX LLC Snap handheld magnetic field survey meter.

[00416] The fast settling time and low C-SWAP of the DNV sensor enables rapid measurement of detailed power line characteristics from low-C-SWAP UAS systems. In one or more implementations, power lines can be efficiently surveyed via small unmanned aerial vehicles (UAVs) on a routine basis over long distance, which can identify emerging problems and issues through automated field anomaly identification. In other implementations, a land based vehicle or submersible can be used to inspect power lines. Human inspectors are not required to perform the initial inspections. The inspections of the subject technology are quantitative, and thus are not subject to human interpretation as remote video solutions may be.

[00417] Figure 52 illustrates an example of a measured magnetic field distribution for power lines 904 and power lines with anomalies 902 according to some implementations. The peak value of the measured magnetic field distribution, for the normal power lines, is in the vicinity of the centerline (e.g., d = 0). The inspection method of the subject technology is a high-speed anomaly mapping technique that can be employed for single and multi-wire transmission systems. The subject solution can take advantage of existing software modeling tools for analyzing the inspection data. In one or more implementations, the data form a normal set of power lines may be used as a comparison reference for data resulting from inspection of other power lines (e.g., with anomalies or defects). Damage to wires and support structure alters the nominal magnetic field characteristics and is detected by comparison with nominal magnetic field characteristics of the normal set of power lines. It is understood that the magnetic field measurement is minimally impacted by other structures such as buildings, trees, and the like. Accordingly, the measured magnetic field can be compared to the data from the normal set of power lines and the measured magnetic field's magnitude and if different by a predetermined threshold the existence of the anomaly can be indicated. In addition, the vector reading between the difference data can also be compared and used to determine the existence of anomaly.

[00418] In some implementations, a vehicle may need to avoid objects that are in their navigation path. For example, a ground vehicle may need to maneuver around people or objects, or a flying vehicle may need to avoid a building or power line equipment. In these implementations, the vehicle can be equipment with sensors that are used to locate the obstacles that are to be avoided. Systems such as a camera system, focal point array, radar, acoustic sensors, etc., can be used to identify obstacles in the vehicles path. The navigation system can then identify a course correction to avoid the identified obstacles.

[00419] MEASUREMENT PARAMETERS FOR QC METROLOGY OF SYNTHETICALLY GENERATED DIAMOND WITH NV CENTERS

[00420] Measuring the quantum energy levels of a diamond nitrogen vacancy (DNV) material may provide information regarding the quality of the material, such as the suitability of the DNV material for use in a magnetic field sensor. The impurity content, lattice strain, and nitrogen vacancy (NV) concentration of the DNV material impact the quantum energy levels of the DNV material. Thus, measuring the quantum energy levels of the DNV material provides information regarding the impurity content, lattice strain, and NV content of the DNV material.

[00421] Characterization of DNV material [00422] The characterization of DNV materials may be achieved by measuring a number of parameters associated with the fluorescence behavior described above. For example, DNV metrology may be carried out through the measurement of a number of parameters associated with the Zero-Field-Splitting (ZFS) of the DNV dipolar coupling and the Hyperfine coupling of the DNV material. The measurement of these parameters allows assessment of the impurities in the diamond. Examples of the impurities are lattice dislocations, broken bonds, and other elements beyond 14-Nitrogen. Measurement of these parameters further affords insight as to the concentration of DNV centers. Impurities and excess DNV concentration directly impact the hyperfme resolution. Lattice dislocations and crystal strain can affect the ZFS level by introducing an asymmetry that breaks the degeneracy of the state. The assessment pursued by the measurements maybe conducted in a reasonably short period of time, and provides sufficient depth of information such that the quality of the DNV material may be confirmed. Such a quality assurance (QA) assessment is desirable when evaluating and comparing various DNV suppliers or when confirming the properties of DNV materials.

[00423] The characterization of a DNV sample includes measurements of the quantum nature of the sample. The ZFS parameters are derived from the Hamiltonian (Energy Equation) to a specific precision for the DNV system. The Hamiltonian can be expressed as:

where:

The Zeeman term describes the interaction of the spin centers with an external magnetic field. Measurements of the terms D, A, and Q provide significant insight into the repeatability and quality of the DNV manufacturing process.

[00424] A schematic depiction of the energy levels of the DNV Hamiltonian is shown in FIG. 53. In the diagram of FIG. 53, the DNV ground state level and various splitting of the energy levels due to different couplings such as dipolar couplings (with E=0 and E>0), hyperfme coupling, and quadrupole coupling are shown.

[00425] The terms

and

provide insight into the repeatability and quality of the DNV manufacturing process because the terms

and

from the Hamiltonian equation are measurable quantities that determine the energy levels of the DNV system. In the DNV reference frame aligned to the NV center, the

tensor may be expressed as:

where the parameter D is the ZFS amount. D typically has a value of -2.870 GHz. The parameter E is an additional symmetry breaking term, and may be on the order of a few MHz. Combining these two parameters provides information regarding the degree of strain in the diamond lattice. FIG. 54 is a diagram illustrating an example of a DNV fluorescence signal as described above without an applied bias field (0 gauss bias). The parameters E and D are derived from the measured frequencies vi and v2 of the DNV optical signal of FIG. 54 according to following equations:

[00426] The measured frequencies vx and v2 of the DNV signal may be considered to be the location of lorentzian peaks in the DNV optical signal, as shown in FIG. 54.

[00427] To produce a fluorescence signal of the DNV material, a continuous wave (CW) laser pumping and a continuous-wave (CW) radio-frequency (RF) can be employed for excitation of the DNV sample, in the absence of an applied bias magnetic field. The RF signal can be swept from - 2.8 to 2.95 GHz to observe the fluorescence signal shown in FIG. 54.

[00428] The A tensor of the Hamiltonian is associated with the hyperfine splitting shown in FIG. 55. Identifying and measuring hyperfine values provides information regarding the purity of the DNV sample and the concentration of N/NV. FIGS. 55 and 56 are diagrams illustrating DNV florescence signals for a high quality DNV sample and a low quality DNV sample, respectively, under a 1 Gauss magnetic bias field. The locations of the hyperfine levels may indicate the presence of isotopes of 15N, 14N, and 13C in the DNV sample. The natural isotope 14N has known levels of approximately +2.5 MHz, 0 MHz, and -2.5 MHz relative to the dipolar energy levels, as shown in FIG. 55. The ability to resolve hyperfine levels at room temperature, as seen in FIG. 55, indicates a high purity of the DNV sample. A high purity DNV sample may allow hyperfine levels to be resolved without cooling the DNV sample to cryogenic temperatures. Samples with low purity or high N/NV concentration effectively blur the hyperfine peaks such that they are unresolvable, as shown in FIG.56. The inability to resolve hyperfine levels is an indication of a low purity or high defect DNV sample.

[00429] To determine the existence of the hyperfine resonance, a small bias magnetic field is applied to the DNV sample along with continuous wave (CW) laser pumping and a CW RF excitation. In some implementations, the RF power may be beneficially adjusted to the lowest setting possible while still obtaining measurable resonances. The RF signal can be swept from ~2.8 to 2.95 GHz to observe the fluorescence signal shown in FIG. 55, which utilized a 1 gauss bias magnetic field. The bias magnetic field applied to identify and measure the hyperfine splitting may be any appropriate bias field, such as at least about 1 gauss, or about 30 gauss.

[00430] FIG. 6 is a schematic of an NV center sensor 600, according to some embodiments. The sensor 600 includes an optical excitation source 610, which directs optical excitation to an NV diamond material 620 with NV centers. An RF excitation source 630 provides RF radiation to the NV diamond material 620. The NV center sensor 600 may include a bias magnetic field source 670, such as a permanent magnet or electromagnet, applying a bias magnetic field to the NV diamond material 620. Light from the NV diamond material 620 may be directed through an optical filter 650 and an electromagnetic interference (EMI) filter 660, which suppresses conducted interference, to an optical detector 640. The sensor 600 further includes a controller 680 arranged to receive a light detection signal from the optical detector 640 and to control the optical excitation source 610 and the RF excitation source 630.

[00431] The RF excitation source 630 may be a microwave coil, for example. The RF excitation source 630 is controlled to emit RF radiation with a photon energy resonant with the transition energy between the ground ms = 0 spin state and the ms = ±1 spin states as discussed above with respect to FIG. 3 [00432] The optical excitation source 610 may be a laser or a light emitting diode, for example, which emits light in the green band, for example. The optical excitation source 610 induces fluorescence of the NV diamond material in the red band, which corresponds to an electronic transition from the excited state to the ground state. Light from the NV diamond material 620 is directed through the optical filter 650 to filter out light in the excitation band (in the green for example), and to pass light in the red fluorescence band, which in turn is detected by the optical detector 640. The EMI filter 660 is arranged between the optical filter 650 and the optical detector 640 and suppresses conducted interference. The optical excitation light source 610, in addition to exciting fluorescence in the NV diamond material 620, also serves to reset the population of the ms = 0 spin state of the ground state 3A2 to a maximum polarization, or other desired polarization.

[00433] The controller 680 is arranged to receive a light detection signal from the optical detector 640 and to control the optical excitation source 610 and the RF excitation source 630. The controller may include a processor 682 and a memory 684, in order to control the operation of the optical excitation source 610 and the RF excitation source 630. The memory 684, which may include a nontransitory computer readable medium, may store instructions to allow the operation of the optical excitation source 610 and the RF excitation source 630 to be controlled.

[00434] According to some embodiments of operation, the controller 680 controls the operation such that the optical excitation source 610 continuously pumps the NV centers of the NV diamond material 620. The RF excitation source 630 is controlled to continuously sweep across a frequency range which includes the zero splitting (when the ms = ±1 spin states have the same energy) photon energy of 2.87 GHz. When the photon energy of the RF radiation emitted by the RF excitation source 630 is the difference in energies of the ms = 0 spin state and the ms = -1 or ms = +1 spin state, the overall fluorescence intensity is reduced at resonance, as discussed above with respect to FIG. 3. In this case, there is a decrease in the fluorescence intensity when the RF energy resonates with an energy difference of the ms = 0 spin state and the ms = -1 or ms = +1 spin states.

[00435] According to some embodiments, the NV center sensor 600 may also function as a magnetic field sensor. As noted above, the diamond material 620 will have NV centers aligned along directions of four different orientation classes, and the component Bz along each of the different orientations may be determined based on the difference in energy between the ms = -1 and the ms = +1 spin states for the respective orientation classes. In certain cases, however, it may be difficult to determine which energy splitting corresponds to which orientation class, due to overlap of the energies, etc. The bias magnetic field source 670 provides a magnetic field, which is preferably uniform on the NV diamond material 620, to separate the energies for the different orientation classes, so that they may be more easily identified. In this way the component of the magnetic field Bz along the NV axis may be determined by the difference in energies between the ms = -1 and the ms = +1 spin states.

[00436] DNV material assessment systems [00437] The assessment of the DNV material may take place in a dedicated test system prior to incorporation of the DNV material in a sensor system or after the DNV material has been incorporated in a sensor system, such as a magnetic field sensor. The use of a dedicated test system allows the DNV material to be evaluated after production or upon receipt from a supplier. In this manner it can be assured that the DNV material exhibits the desired properties before incorporation in to a device. Assessing the DNV material after incorporation in a sensor system allows the condition of the DNV material to be monitored throughout the lifetime of the sensor system. This arrangement allows the DNV material to be monitored and a user alerted if the DNV material is damaged or degrades to an extent that the accuracy or operation of the sensor system would be negatively impacted.

[00438] A dedicated test system for assessment of the DNV material may include the features of the NV sensor system depicted in FIG. 6 and described above. As described above, the zero field splitting (ZFS) amount of the DNV material is measured in the absence of an external magnetic field. For the measurement of ZFS amount, the bias magnetic field source 670 may be omitted from the sensor system. Alternatively, a switchable bias magnetic field source 670, such as an electromagnet, may be employed in the off state when measuring the ZFS amount. Magnetic shielding may be included in the sensor system to reduce or eliminate the magnetic field acting on the DNV material during the measurement of the ZFS amount.

[00439] The test system may include a controller of the type depicted in FIG. 6. The controller may be programmed to control the optical excitation source and the RF excitation source to produce a luminescence signal at the optical detector. The controller is also programmed to determine the ZFS amount, D and E from the luminescence signal received by the optical detector in the manner described above. During the measurement of the ZFS amount, D and E, a magnetic bias field is not applied to the DNV material.

[00440] The test system may include an automated system for disposing the DNV material in the test system. The automated system may include any component capable of disposing the DNV material in the test system. Alternatively, the test system may be configured such that a user can place the DNV sample in the test system.

[00441] As described above, the ZFS amount, D and E provide insight into the degree of strain in the crystal lattice of the DNV material. The controller may be programmed to determine the degree of strain in the crystal lattice of the DNV material based on the measured ZFS amount, D and E. Determining the degree of strain in the crystal lattice may include comparing the measured ZFS amount, D and E to pre-determined threshold values stored in the memory of the controller. In the case that the measured ZFS amount, D and E fall within the range defined by the threshold values, the degree of strain in the crystal lattice of the DNV material is determined to be acceptable.

[00442] The ZFS amount, D and E also provide insight into the concentration of crystal lattice defects present in the DNV material. The controller may be programmed to determine the concentration of crystal lattice defects in the crystal lattice of the DNV material based on the measured ZFS amount, D and E. Determining the concentration of crystal lattice defects in the crystal lattice may include comparing the measured ZFS amount, D and E to pre-determined threshold values stored in the memory of the controller. In the case that the measured ZFS amount, D and E fall within the range defined by the threshold values, the concentration of crystal lattice defects in the crystal lattice of the DNV material is determined to be acceptable. The threshold values for ZFS amount, D and E may be any appropriate value that is associated with a DNV material that exhibits the desired properties. For example, a threshold value for D may be between 2.5 and 5.5 MHz.

[00443] The controller may be programmed to determine whether hyperfines are resolvable in a luminescence signal received at the optical detector when a magnetic bias is applied to the DNV material. The controller may be programmed to control the optical excitation source and the RF excitation source to produce the luminescence signal at the optical detector.

Additionally, the controller may be programmed to control a magnetic bias generator, such that a magnetic bias field is applied to the DNV material. The magnetic bias field applied to the DNV material may be a small magnetic bias field, such as ~30 gauss. The test system utilized to determine whether hyperfines are resolvable may be the same test system employed to measure the ZFS amount, D and E. Alternatively, the test system utilized to determine whether hyperfines are resolvable may be a different test system than the test system employed to measure the ZFS amount, D and E.

[00444] As described above, the ability to resolve hyperfines in the luminescence signal received at the optical detector provides insight as the concentration of NV centers and impurities in the DNV material. A hyperfine may be considered to be resolvable when the full width half maximum value for the hyperfine is measurable from the luminescence signal received at the optical detector. The ability to resolve hyperfines indicates that the concentration of NV centers and impurities in the DNV material is in an acceptable range. Impurities may be considered the inclusion of components in the DNV material that deviate from the intent of manufacture.

[00445] In some cases, the presence of hyperfines in addition to those associated with the natural isotope 14N shown in FIG. 55 may indicate that additional impurity species are present in the DNV material. For example, hyperfines at other locations in the luminescence signal may indicate that isotopes of 15N, and/or 13C are present in the DNV sample. In general, the ability to resolve hyperfines in the luminescence signal indicates that the DNV material is of sufficient purity. According to some embodiments, where a high purity DNV material including 14N and 12C is desired 15N and 13C isotopes are considered impurities. According to some other embodiments, where a high purity DNV material including 15N and 12C is desired 14N and 13C isotopes are considered impurities.

[00446] The assessment of the DNV material may be carried out in a sensor system. For example, the controller of a DNV magnetic field sensor may be programmed to measure the ZFS amount, D and E and determine whether hyperfines can be resolved as described above. The result of the measurement of ZFS amount, D and E may be compared to a threshold value stored in a memory of the controller. In the event that the measured values fall outside of the desired threshold value ranges, an error message may be communicated to a user of the sensor system. Similarly, if hyperfines are not capable of being resolved, an error message may be communicated to a user of the sensor system. The error message may be communicated to a user by any appropriate means, such as a display, error light, or wireless communication. The ability to resolve hyperfines may be considered to indicate that a concentration of NV centers in the DNV material and/or a concentration of impurities in the DNV material are within a desired range. The ability to resolve hyperfines may indicate a concentration on the order of at least parts per million.

[00447] The assessment of the DNV material in the sensor system may be carried out periodically. For example, the assessment may be carried out hourly or daily while the sensor is in use. Alternatively, the assessment of the DNV material may be carried out when the sensor is moved or has been subjected to an event that may have damaged the DNV material. In this manner, the assessment of the DNV material may be carried out throughout the lifetime of the sensor system. This ensures that the DNV material produces acceptable performance over the lifetime of the sensor system. The performance of the sensor system may be negatively impacted if the DNV material exhibits an increased strain, concentration of crystal lattice defects, concentration of impurities, or change in NV center concentration. The assessment of the DNV material throughout the lifetime of the sensor system warns a user of such an occurrence.

[00448] The result of the assessment of the DNV material may be stored in a memory of the controller. The stored assessment results may then be utilized to monitor a trend in the properties of the DNV material over time. This information may provide insight into potential future problems with the DNV material in the sensor system, or provide a warning regarding the degradation of the DNV material. For example, an increase in the degree of strain in the crystal lattice over time may indicate that a stress induced fracture of the DNV material is imminent.

[00449] The DNV assessment systems and methods described herein are capable of quickly and non-destructively performing quality control checks on DNV materials. The systems are capable of sufficient throughput to operate in line with a DNV sensor manufacturing line, and provide sufficient information regarding the properties of the DNV material to establish that the DNV material is acceptable for use.

[00450] APPARATUS AND METHOD FOR CLOSED LOOP PROCESSING FOR A MAGNETIC DETECTION SYSTEM

[00451] Described below are apparatuses and methods for elucidating hyperfme transition responses to determine an external magnetic field acting on a magnetic detection system. The hyperfme transition responses may exhibit a steeper gradient than the gradient of aggregate Lorentzian responses measured in conventional systems, which can be up to three orders of magnitude larger. Thus, the hyperfme responses can allow for greater sensitivity in detecting changes in the external magnetic field. In certain embodiments, the detection of the hyperfme responses is then used in a closed loop processing to estimate the external magnetic field in realtime. This may be done by applying a compensatory field via a magnetic field generator controlled by a controller that offsets any shifts in the hyperfme responses that occur due to changes in the external magnetic field. In the closed loop processing, the controller continually monitors the hyperfme responses and, based on a computed estimated total magnetic field acting on the system, provides a feedback to the magnetic field generator to generate a compensatory field that is equal and opposite in sign to the vector components of the external magnetic field in order to fix the hyperfine responses despite changes in the external magnetic field. This, in turn, provides a real-time calculation of the external magnetic field in the form of the calculated inverted compensatory field. Moreover, by fixing the hyperfine responses despite changes in the external magnetic field, a smaller bias magnetic field, which separates out the hyperfine responses to provide sufficient spacing for tracking purposes, may be utilized. The application of a smaller bias magnetic field reduces the frequency range needed for the radiofrequency excitation sweep and measurement circuits, thus providing a system that is more responsive and efficient in determining the external magnetic field acting on the system.

The Hyperfine Field [00452] As discussed above and shown in the energy level diagram of FIG. 2, the ground state is split by about 2.87 GHz between the ms = 0 and ms = ±1 spin states due to their spin-spin interactions. In addition, due to the presence of a magnetic field, the ms = ±1 spin states split in proportion to the magnetic field along the given axis of the NV center, which manifests as the four-pair Lorentzian frequency response shown in FIG. 5. However, a hyperfine structure of the NV center exists due to the hyperfine coupling between the electronic spin states of the NV center and the nitrogen nucleus, which results in further energy splitting of the spin states. FIG. 8 shows the hyperfine structure of the ground state triplet 3A2 of the NV center. Specifically, coupling to the nitrogen nucleus 14N further splits the ms = ±1 spin states into three hyperfine transitions (labeled as mi spin states), each having different resonances. Accordingly, due to the hyperfine split for each of the ms = ±1 spin states, twenty-four different frequency responses may be produced (three level splits for each of the ms = ±1 spin states for each of the four NV center orientations).

[00453] Each of the three hyperfine transitions manifest within the width of one aggregate Lorentzian dip. With proper detection, the hyperfine transitions may be elucidated within a given Lorentzian response. To detect such hyperfine transitions, in particular embodiments, the NV diamond material 620 exhibits a high purity (e.g., low existence of lattice dislocations, broken bonds, or other elements beyond 14N) and does not have an excess concentration of NV centers. In addition, during operation of the system 600 in some embodiments, the RF excitation source 630 is operated on a low power setting in order to further resolve the hyperfine responses. In other embodiments, additional optical contrast for the hyperfme responses may be accomplished by increasing the concentration of NV negative-charge type centers, increasing the optical power density (e.g., in a range from about 20 to about 1000 mW/mm2), and decreasing the RF power to the lowest magnitude that permits a sufficient hyperfme readout (e.g., about 1 to about 10 W/mm2).

[00454] FIG. 9 shows an example of fluorescence intensity as a function of an applied RF frequency for an NV center with hyperfme detection. In the top graph, the intensity response /(t) as a function of an applied RF frequency f(t) for a given spin state (e.g., ms = -1) along a given axis of the NV center due to an external magnetic field is shown. In addition, in the bottom graph, the gradient

plotted against the applied RF frequency f(t) is shown. As seen in the figure, the three hyperfme transitions 200a-200c constitute a complete Lorentzian response 20 (e.g., corresponding to the Lorenztian response 20 in FIG. 7). The point of maximum slope may then be determined through the gradient of the fluorescence intensity as a function of the applied RF frequency, which occurs at the point 250 in FIG. 9. This point of maximum slope may then be tracked during the applied RF sweep to detect movement of the point of maximum slope along the frequency sweep. Like the point of maximum slope 25 for the aggregate Lorentzian response, the corresponding movement of the point 250 corresponds to changes in the total incident magnetic field Bt(t), which because of the known and constant bias field Bbias(t), allows for the detection of changes in the external magnetic field Bext(t).

[00455] However, as compared to point 25, point 250 exhibits a larger gradient than the aggregate Lorentzian gradient described above with regard to FIG. 7. In some embodiments, the gradient of point 250 may be up to 1000 times larger than the aggregate Lorentzian gradient of point 25. Due to this, the point 250 and its corresponding movement may be more easily detected by the measurement system resulting in improved sensitivity, especially in very low magnitude and/or very rapidly changing magnetic fields.

Closed Loop Processing of External Magnetic Field [00456] As discussed above, current methods in determining the total incident magnetic field Bt(t) examine the fluorescence intensity as a function of applied RF frequency based on the movement of the point of greatest gradient of the aggregate Lorentzian response (e.g., point 25 of Lorentzian dip 20 of FIG. 7). By fine-tuning the point of measurement to be the hyperfine transition, greater sensitivity in this tracking may be achieved. An example of an open-loop or ad-hoc processing method to estimate the vector components of the total magnetic field Bt(t) on the NV center magnetic sensor system is shown in FIG. 10.

[00457] When in a zero magnetic field (i.e., Bt(t) = 0), the Lorentzian responses for each of the ms = ±1 spin states along the four axes of the NV center overlap at the same frequency (e.g., about 2.87 GHz). To pre-separate and space (e.g., equally) the eight Lorentzian responses for tracking purposes, a bias or control magnetic field Bbias(t) may be applied. The first magnetic field generator (e.g., a permanent magnet) 670 and/or the second magnetic field generator (e.g., a three-axis Cartesian Bbias(t) Helmholtz coil system) 675, as shown in the system 600 of FIG. 6, may be used to apply the desired bias field. As discussed above, the second magnetic field generator 675 is electrically connected to the controller 680, by which the magnetic field produced by the second magnetic field generator 675 may be controlled by the controller 680.

[00458] As shown in FIG. 57, during the open-loop processing, the sum of the external magnetic field Bext(t) and the bias magnetic field Bbias(t), represented by the total incident magnetic field Bt(t), acts on the NV center magnetic sensor system 600, which linearly converts to an intensity response /(t) due to the Zeeman effect Z that, in conjunction with the applied RF frequency /(t), results in the aggregate Lorentzian curves or the Lorentzian hyperfine curves at the corresponding resonance frequencies, as discussed in greater detail above. Processing is then performed by the system controller 680 by operating on the Lorentzian gradient to determine an estimate of the total incident magnetic field B(t). The total incident magnetic field may be linearly expressed as:

(1) [00459] Where, in equation (1), γ represents the nitrogen vacancy gyromagnetic ratio of about 28 GHz/T. The maximum gradient or slope may be determined by the Jacobian operator evaluated at a critical frequency fc where the Lorentzian aggregate or hyperfine slope is the greatest: [00460] The critical frequency fc is determined analytically based on the NV diamond material 620 incorporated into the sensor system and is pre-stored in the controller 680 for processing purposes. Thus, the total incident magnetic field may be estimated according to the critical frequency:

(3) [00461] As can be seen from equations (1) to (3), the relationship between the actual total incident field Bt(t) and the estimated total incident field Bt(t) is more accurate the larger the intensity to frequency gradient magnitude. Thus, by evaluating the critical frequency fc at the point of greatest slope of the hyperfine response, rather than the point of greater slope of the aggregate Lorentzian response, a more accurate estimation of the total incident field Bt(t) may be obtained.

[00462] However, at this point, computing the difference in effect on the Lorentzian responses from the bias magnetic field Bbias(t) and the external magnetic field Bext(t) is difficult as the total vector sum of the two fields cause the overall shift between Lorentzian responses. Thus, the open-loop or ad-hoc method shown in FIG. 64 relies on continuous tracking to determine the external magnetic field vector Bext(t) based on subtraction of the known bias control magnetic field Bbias(t) from the total estimated incident field Bt(t). The determination of the external magnetic field vector Bext(t), however, may be affected due to sensitivity to external in-band and corrupting disturbance fields or related Hamiltonian effects (e.g., temperature, strain). Moreover, the above open loop method requires constant re-calibration and compensation during measurement.

[00463] FIGS. 58 and 59 show a closed loop processing performed by the controller 680 according to an exemplary embodiment of the present invention. The closed loop processing described herein allows the estimated total incident magnetic field Bt(t) to be computed in realtime and actuated through the second magnetic field generator 675 to create a compensatory field Bcomp(t). This compensatory field may then be used to offset the shifts in RF response by the external magnetic field Bext(t) to produce a fluorescence response that remains constant and fixed, thus reducing the need for constant tracking of the response shifts. As a result, the compensatory field, which is the external magnetic field Bext(t) with an inverted sign, allows for the measurement and computation of the external magnetic field Bext(t) in real-time. FIG. 58 is a schematic diagram showing the closed loop processing using the compensatory field, while FIG. 59 is a flowchart depicting a method in performing the closed loop processing shown in FIG. 58.

[00464] As shown in FIG. 59, in a step S5900, a bias field Bbias(t) is applied to separate out the Lorentzian responses at desired frequencies (e.g., equally-spaced frequencies). As discussed above, the bias field may be applied using the first magnetic field generator 670 (e.g., a permanent magnet), which is known and constant. However, the bias field may alternatively be applied by the second magnetic field generator 675. In this case, an initial calibration offset R (shown in FIG. 58), in the form of a constant, is added to the driver G, which drives the second magnetic field generator 675 to generate the bias field necessary to separate the Lorentzian hyperfine responses. Once this is set, the closed loop processing may proceed to a step S5910, where the unknown external magnetic field Bext(t) is read. As shown in FIG. 58, this step may be performed in a similar manner as the processing described with regard to FIG. 57, where an estimated total incident magnetic field Bt(t) is computed by evaluating the gradient of the intensity response /(t) as a function of applied frequency f(t) at the critical frequency.

[00465] In a step S5920, shifts in the hyperfine responses are observed. Largest changes per a predetermined sampling period may be identified in order to identify the vector direction of the unknown magnetic field. The observed shifts may then be used to close the loop processing as shown in FIG. 58. Specifically, the closed loop processing includes a feedback controller block H along with an input of an arbitrary calibration reference R(t), which is set to 0 under normal operation but may be adjusted to collocate the Lorentzian responses (e.g., hyperfine responses) with as many vector components of the unknown external field as possible, and a driver block G. The feedback H and driver G serve as transfer functions to output a signal to the second magnetic field generator 675 to generate the compensatory field Bcomp(t) that represents the magnetic field needed to ensure that the largest gradient of the response remains fixed in terms of intensity response, thereby offsetting any shifts due to the external magnetic field Bext(i). Thus, as shown in FIG. 59, in a step S5930, the loop is closed by increasing the controller net spectral gain. Loop closure may be achieved with the feedback H and driver G set as either constant gains (e.g., a Luenberger Observer) or state and measurement noise covariance driven variable gains (e.g., a Kalman filter) or a non-linear gain scheduled observer or the like, where each control system embodiment may be tailored to the specific application. In a step S5940, a compensatory field Bcomp(t) is stored with an inverted sign to the shift observed in step S5920. Because this compensatory field Bcomp(t) represents an equal, but opposite, magnetic field as the unknown external field Bext(t), the inverse of the compensatory field Bcomp(t) may be subsequently exported in a step S5941 and stored in the controller 680 as the external field Bext(t) impinging on the system 600. In a step S5950, the controller net spectral gain is further increased to drive the compensatory field Bcomp(t) to lock to the external field Bext(t) such that the observed intensity response remains fixed. The process then repeats by continuing to step S5910. Such a processing allows for the compensatory field Bcomp(t) stored by the controller 680 to offset any shifts in the intensity response caused by the external field Bext(t), resulting in real-time computation of the external field by virtue of this processing.

[00466] The loop algebra for the closed loop processing may be represented as follows. As stated above, the total incident magnetic field is represented by the sum total of the unknown external field and the sum of the bias field and the compensatory field that is applied when the loop is closed. Because the bias field is constant over time, for the purposes of evaluating the required compensatory field needed for the closed loop processing, the bias field will be excluded in the loop algebra below. Thus, the total incident field may be represented by: ^t(t) — Bext(t) + Bcomp(t') (4) [00467] Because of the linear relationship between the intensity response /(t) and the total incident magnetic field Bt(t) acting on the NV diamond material 620 due to the Zeeman effect, equation (3) may be expressed as: [00468] Loop closure based on the estimated total magnetic field Bt(t) in order to produce the compensatory field Bcomp(t) using the feedback and driver gains and the calibration reference may be expressed as follows:

Bcomp{t) = G{R-HBt{t)) (6) [00469] Combining equations (4) to (6) results in:

(7) [00470] During normal operation of the closed loop processing, the calibration reference R will not vary over time and will be 0. Thus, equation (7) may be reduced as follows:

(8) (9) (10) [00471] As can be seen from equation (10), as the gradient of the intensity response /(t) becomes larger at the critical frequency, the relationship between the compensatory field BComp(0 and the unknown external field Bext(t) will approach 1, such that Bcomp(t) = —Bext(t). Thus, by use of the hyperfine responses, which exhibit a largest slope that may be three orders of magnitude greater than the largest slope of the aggregate Lorentzian responses, such a relationship may be achieved with the closed loop processing. This, in turn, allows for an unknown external field Bext(t) to be measured and computed in real time by virtue of the loop gain equivalent actuation of the second magnetic field generator 675 by the controller 680 using the compensatory field Bcomp(t) with an inverted sign.

[00472] While the transfer functions G and H are shown as constant operators in equations (6) to (10) and FIG. 58, the transfer functions can both be realized by analog circuitry as continuous, time invariant system functions in the frequency domain such as, for example, G(s): s = a + bi, where s is the Laplace operator. Alternatively, the control system may implemented in a digital computer that executes sampling and computation at regular time intervals of T seconds, where the transfer function G(z) may be defined with z = exp(sT) being the zdomaindiscrete sampled data frequency domain operator.

[00473] As described above, the control loop processing of the system 600 provides a means to fix the hyperfine responses despite changes in the external magnetic field. By dynamically fixing the responses, a smaller bias magnetic field may be utilized, while still retaining a robust means to detect and calculate changes due to the external magnetic field. The application of a smaller bias magnetic field, in turn, reduces the frequency range needed for the RF excitation sweep and measurement circuits of the intensity response, which provides a system that is more responsive and efficient in determining the external magnetic field acting on the system. In addition, the range of signal amplitudes to which the system can detect and respond to quickly and accurately may be significantly improved, which can be especially important for large amplitude magnetic field applications.

[00474] APPARATUS AND METHOD FOR HIGH SENSITIVITY MAGNETOMETRY

MEASUREMENT AND SIGNAL PROCESSING IN A MAGNETIC DETECTION SYSTEM

[00475] Described below are apparatuses and methods for stimulating a NV diamond in a magnetic detection system using an optimized stimulation process to significantly increase magnetic sensitivity of the detection system. The system utilizes a Ramsey pulse sequence to detect and measure the magnetic field acting on the system. Parameters relating to the Ramsey pulse sequence are optimized before measurement of the magnetic field. These parameters include the resonant Rabi frequency, the free precession time (tau), and the detuning frequency, all of which help improve the sensitivity of the measurement. These parameters may be optimally determined using calibration tests utilizing other optical detection techniques, such as a Rabi pulse sequence or additional Ramsey sequences. In addition, parameters, in particular the resonant Rabi frequency, may be further optimized by an increase in power of the RF excitation source, which may be achieved through the use of a small loop antenna. During measurement of the magnetic field, the RF excitation pulses applied during the Ramsey sequences may be set to occur at separate resonance frequencies associated with different spin states (e.g., ms = +1 or ms = -1). By utilizing separate resonance locations, changes due to temperature and/or strain effects in the system and changes due to the external magnetic field may be separated out, thus improving the accuracy of the measurements. Finally, processing of the data obtained during measurement is further optimized by the use of at least two reference windows, the average of which is used to obtain the signal. The above provide a magnetic detection system capable of improved sensitivity in detection of a magnetic field. In some embodiments, the optimized measurement process may result in a sensitivity of the magnetic detection system of about

or less.

The NV Center, Its Electronic Structure, and Optical and RF Interaction [00476] The NV center in a diamond comprises a substitutional nitrogen atom in a lattice site adjacent a carbon vacancy as shown in FIG. 1. The NV center may have four orientations, each corresponding to a different crystallographic orientation of the diamond lattice.

[00477] The NV center may exist in a neutral charge state or a negative charge state. Conventionally, the neutral charge state uses the nomenclature NV°, while the negative charge state uses the nomenclature NV, which is adopted in this description.

[00478] The NV center has a number of electrons, including three unpaired electrons, each one from the vacancy to a respective of the three carbon atoms adjacent to the vacancy, and a pair of electrons between the nitrogen and the vacancy. The NV center, which is in the negatively charged state, also includes an extra electron.

[00479] The NV center has rotational symmetry, and as shown in FIG. 2, has a ground state, which is a spin triplet with 3A2 symmetry with one spin state ms = 0, and two further spin states ms = +1, and ms = -1. In the absence of an external magnetic field, the ms = ±1 energy levels are offset from the ms = 0 due to spin-spin interactions, and the ms = ±1 energy levels are degenerate, i.e., they have the same energy. The ms = 0 spin state energy level is split from the ms = ±1 energy levels by an energy of 2.87 GHz for a zero external magnetic field.

[00480] Introducing an external magnetic field with a component along the NV axis lifts the degeneracy of the ms = ±1 energy levels, splitting the energy levels ms = ±1 by an amount 2gpBBz, where g is the g-factor, μΒ is the Bohr magneton, and Bz is the component of the external magnetic field along the NV axis. This relationship is correct to a first order and inclusion of higher order corrections is a straightforward matter and will not affect the computational and logic steps in the systems and methods described below.

[00481] The NV center electronic structure further includes an excited triplet state 3E with corresponding ms = 0 and ms = ±1 spin states. The optical transitions between the ground state 3A2 and the excited triplet 3E are predominantly spin conserving, meaning that the optical transitions are between initial and final states that have the same spin. For a direct transition between the excited triplet 3E and the ground state 3A2, a photon of red light is emitted with a photon energy corresponding to the energy difference between the energy levels of the transitions.

[00482] There is, however, an alternative non-radiative decay route from the triplet 3E to the ground state 3A2 via intermediate electron states, which are thought to be intermediate singlet states A, E with intermediate energy levels. Significantly, the transition rate from the ms = ±1 spin states of the excited triplet 3E to the intermediate energy levels is significantly greater than the transition rate from the ms = 0 spin state of the excited triplet 3E to the intermediate energy levels. The transition from the singlet states A, E to the ground state triplet 3A2 predominantly decays to the ms = 0 spin state over the ms = ±1 spins states. These features of the decay from the excited triplet 3E state via the intermediate singlet states A, E to the ground state triplet 3A2 allows that if optical excitation is provided to the system, the optical excitation will eventually pump the NV center into the ms = 0 spin state of the ground state 3A2. In this way, the population of the ms = 0 spin state of the ground state 3A2 may be “reset” to a maximum polarization determined by the decay rates from the triplet 3E to the intermediate singlet states.

[00483] Another feature of the decay is that the fluorescence intensity due to optically stimulating the excited triplet 3E state is less for the ms = ±1 states than for the ms = 0 spin state. This is so because the decay via the intermediate states does not result in a photon emitted in the fluorescence band, and because of the greater probability that the ms = ±1 states of the excited triplet 3E state will decay via the non-radiative decay path. The lower fluorescence intensity for the ms = ±1 states than for the ms = 0 spin state allows the fluorescence intensity to be used to determine the spin state. As the population of the ms = ±1 states increases relative to the ms = 0 spin, the overall fluorescence intensity will be reduced.

The NV Center, or Magneto-Optical Defect Center, Magnetic Sensor System [00484] FIG. 3 is a schematic diagram illustrating a conventional NV center magnetic sensor system 300 that uses fluorescence intensity to distinguish the ms = ±1 states, and to measure the magnetic field based on the energy difference between the ms = +1 state and the ms = -1 state. The system 300 includes an optical excitation source 310, which directs optical excitation to an NV diamond material 320 with NV centers. The system further includes an RF excitation source 330, which provides RF radiation to the NV diamond material 320. Light from the NV diamond may be directed through an optical filter 350 to an optical detector 340.

[00485] The RF excitation source 330 may be a microwave coil, for example. The RF excitation source 330, when emitting RF radiation with a photon energy resonant with the transition energy between ground ms = 0 spin state and the ms = +1 spin state, excites a transition between those spin states. For such a resonance, the spin state cycles between ground ms = 0 spin state and the ms = +1 spin state, reducing the population in the ms = 0 spin state and reducing the overall fluorescence at resonances. Similarly, resonance occurs between the ms = 0 spin state and the ms = -1 spin state of the ground state when the photon energy of the RF radiation emitted by the RF excitation source is the difference in energies of the ms = 0 spin state and the ms = -1 spin state, or between the ms = 0 spin state and the ms = +1 spin state, there is a decrease in the fluorescence intensity.

[00486] The optical excitation source 310 may be a laser or a light emitting diode, for example, which emits light in the green, for example. The optical excitation source 310 induces fluorescence in the red, which corresponds to an electronic transition from the excited state to the ground state. Light from the NV diamond material 320 is directed through the optical filter 350 to filter out light in the excitation band (in the green, for example), and to pass light in the red fluorescence band, which in turn is detected by the detector 340. The optical excitation light source 310, in addition to exciting fluorescence in the diamond material 320, also serves to reset the population of the ms = 0 spin state of the ground state 3A2 to a maximum polarization, or other desired polarization.

[00487] For continuous wave excitation, the optical excitation source 310 continuously pumps the NV centers, and the RF excitation source 330 sweeps across a frequency range that includes the zero splitting (when the ms = ±1 spin states have the same energy) photon energy of 2.87 GHz. The fluorescence for an RF sweep corresponding to a diamond material 320 with NV centers aligned along a single direction is shown in FIG. 4 for different magnetic field components Bz along the NV axis, where the energy splitting between the ms = -1 spin state and the ms = +1 spin state increases with Bz. Thus, the component Bz may be determined. Optical excitation schemes other than continuous wave excitation are contemplated, such as excitation schemes involving pulsed optical excitation, and pulsed RF excitation. Examples of pulsed excitation schemes include Ramsey pulse sequence (described in more detail below), and spin echo pulse sequence.

[00488] In general, the diamond material 320 will have NV centers aligned along directions of four different orientation classes. FIG. 5 illustrates fluorescence as a function of RF frequency for the case where the diamond material 320 has NV centers aligned along directions of four different orientation classes. In this case, the component Bz along each of the different orientations may be determined. These results, along with the known orientation of crystallographic planes of a diamond lattice, allow not only the magnitude of the external magnetic field to be determined, but also the direction of the magnetic field.

[00489] While FIG. 3 illustrates an NV center magnetic sensor system 300 with NV diamond material 320 with a plurality of NV centers, in general, the magnetic sensor system may instead employ a different magneto-optical defect center material, with a plurality of magneto-optical defect centers. The electronic spin state energies of the magneto-optical defect centers shift with magnetic field, and the optical response, such as fluorescence, for the different spin states is not the same for all of the different spin states. In this way, the magnetic field may be determined based on optical excitation, and possibly RF excitation, in a corresponding way to that described above with NV diamond material.

[00490] FIG. 60 is a schematic diagram of a system 6000 for a magnetic field detection system according to an embodiment. The system 6000 includes an optical excitation source 6010, which directs optical excitation to an NV diamond material 6020 with NV centers, or another magneto-optical defect center material with magneto-optical defect centers. An RF excitation source 6030 provides RF radiation to the NV diamond material 6020. A magnetic field generator 6070 generates a magnetic field, which is detected at the NV diamond material 6020.

[00491] The magnetic field generator 6070 may generate magnetic fields with orthogonal polarizations, for example. In this regard, the magnetic field generator 6070 may include two or more magnetic field generators, such as two or more Helmholtz coils. The two or more magnetic field generators may be configured to provide a magnetic field having a predetermined direction, each of which provide a relatively uniform magnetic field at the NV diamond material 6020.

The predetermined directions may be orthogonal to one another. In addition, the two or more magnetic field generators of the magnetic field generator 6070 may be disposed at the same position, or may be separated from each other. In the case that the two or more magnetic field generators are separated from each other, the two or more magnetic field generators may be arranged in an array, such as a one-dimensional or two-dimensional array, for example.

[00492] The system 6000 may be arranged to include one or more optical detection systems 6005, where each of the optical detection systems 6005 includes the optical detector 6040, optical excitation source 6010, and NV diamond material 6020. Furthermore, the magnetic field generator 6070 may have a relatively high power as compared to the optical detection systems 6005. In this way, the optical systems 6005 may be deployed in an environment that requires a relatively lower power for the optical systems 6005, while the magnetic field generator 6070 may be deployed in an environment that has a relatively high power available for the magnetic field generator 6070 so as to apply a relatively strong magnetic field.

[00493] The system 6000 further includes a controller 6080 arranged to receive a light detection signal from the optical detector 6040 and to control the optical excitation source 6010, the RF excitation source 6030, and the second magnetic field generator 6075. The controller may be a single controller, or multiple controllers. For a controller including multiple controllers, each of the controllers may perform different functions, such as controlling different components of the system 6000. The second magnetic field generator 6075 may be controlled by the controller 6080 via an amplifier 6060, for example.

[00494] The RF excitation source 6030 may be a microwave coil, for example. The RF excitation source 6030 is controlled to emit RF radiation with a photon energy resonant with the transition energy between the ground ms = 0 spin state and the ms = ±1 spin states as discussed above with respect to FIG. 3.

[00495] The optical excitation source 6010 may be a laser or a light emitting diode, for example, which emits light in the green, for example. The optical excitation source 6010 induces fluorescence in the red from the NV diamond material 6020, where the fluorescence corresponds to an electronic transition from the excited state to the ground state. Light from the NV diamond material 6020 is directed through the optical filter 6050 to filter out light in the excitation band (in the green, for example), and to pass light in the red fluorescence band, which in turn is detected by the optical detector 6040. The optical excitation light source 6010, in addition to exciting fluorescence in the NV diamond material 6020, also serves to reset the population of the ms = 0 spin state of the ground state 3A2 to a maximum polarization, or other desired polarization.

[00496] The controller 6080 is arranged to receive a light detection signal from the optical detector 6040 and to control the optical excitation source 6010, the RF excitation source 6030, and the second magnetic field generator 6075. The controller may include a processor 6082 and a memory 6084, in order to control the operation of the optical excitation source 6010, the RF excitation source 6030, and the second magnetic field generator 6075. The memory 6084, which may include a nontransitory computer readable medium, may store instructions to allow the operation of the optical excitation source 6010, the RF excitation source 6030, and the second magnetic field generator 6075 to be controlled. That is, the controller 6080 may be programmed to provide control.

Ramsey Pulse Sequence Overview [00497] According to certain embodiments, the controller 6080 controls the operation of the optical excitation source 6010, the RF excitation source 6030, and the magnetic field generator 6070 to perform Optically Detected Magnetic Resonance (ODMR). The component of the magnetic field Bz along the NV axis of NV centers aligned along directions of the four different orientation classes of the NV centers may be determined by ODMR, for example, by using an ODMR pulse sequence according to a Ramsey pulse sequence. The Ramsey pulse sequence is a pulsed RF-pulsed laser scheme that measures the free precession of the magnetic moment in the NV diamond material 6020 and is a technique that quantum mechanically prepares and samples the electron spin state.

[00498] FIG. 61 is a schematic diagram illustrating the Ramsey pulse sequence. As shown in FIG. 61, a Ramsey pulse sequence includes optical excitation pulses and RF excitation pulses over a five-step period. In a first step, during a period 0, a first optical excitation pulse 710 is applied to the system to optically pump electrons into the ground state (i.e., ms = 0 spin state). This is followed by a first RF excitation pulse 720 (in the form of, for example, a microwave (MW) π/2 pulse) during a period 1. The first RF excitation pulse 720 sets the system into superposition of the ms = 0 and ms = +1 spin states (or, alternatively, the ms = 0 and ms = -1 spin states, depending on the choice of resonance location). During a period 2, the system is allowed to freely precess (and dephase) over a time period referred to as tau (τ). During this free precession time period, the system measures the local magnetic field and serves as a coherent integration. Next, a second RF excitation pulse 6140 (in the form of, for example, a MW π/2 pulse) is applied during a period 3 to project the system back to the ms = 0 and ms = +1 basis. Finally, during a period 4, a second optical pulse 6130 is applied to optically sample the system and a measurement basis is obtained by detecting the fluorescence intensity of the system. The RF excitation pulses applied to the system 6000 are provided at a given RF frequency, which correspond to a given NV center orientation. The Ramsey pulse sequence shown in FIG. 66 may be performed multiple times, wherein each of the MW pulses applied to the system during a given Ramsey pulse sequence includes a different frequency that respectively corresponds to a different NV center orientation.

[00499] The theoretical measurement readout from a Ramsey pulse sequence may be defined as equation (a 1) below:

(al) [00500] In equation (al) above, τ represents the free precession time, Γ2* represents spin dephasing due to inhomogeneities present in the system 6000, ωτβε represents the resonant Rabi frequency, represents the effective Rabi frequency, an represents the hyperfme splitting of the NV diamond material 620 (-2.14 MHz), Δ represents the MW detuning, and Θ represents the phase offset.

[00501] When taking a measurement based on a Ramsey pulse sequence, the parameters that may be controlled are the duration of the MW π/2 pulses, the frequency of the MW pulse (which is referenced as the frequency amount detuned from the resonance location, Δ), and the free precession time τ. FIGS. 62A and 62B show the effects on the variance of certain parameters of the Ramsey pulse sequence. For example, as shown in FIG. 62A, if all parameters are kept constant except for the free precession time τ, an interference pattern, known as the free induction decay (FID), is obtained. The FID curve is due to the constructive/destructive interference of the three sinusoids that correspond to the hyperfme splitting. The decay of the signal is due to inhomogeneous dephasing and the rate of this decay is characterized by Γ2 (characteristic decay time). In addition, as shown in FIG. 62B, if all parameters are kept constant except for the microwave detuning Δ, a magnetometry curve is obtained. In this case, the x-axis may be converted to units of magnetic field through the conversion 1 nT = 28 Hz in order to calibrate for magnetometry.

[00502] By varying both τ and Δ, a two-dimensional FID surface plot may be constructed, an example of which is shown in FIG. 63 A. The FID surface plot includes several characteristics that can elucidate optimization of the controllable parameters of the Ramsey sequence. For example, in FIG. 63 A, the FID surface plot is generated using a Γ2 of about 6150 ns and a resonant Rabi frequency of about 6.25 MHz. The horizontal slices of FIG. 63 A represent individual FID curves (e.g., FIG. 62A), while the vertical slices represent magnetometry curves (e.g., FIG. 62B). As shown in FIG. 63 A, FID curves of higher fundamental frequency occur at greater detuning. Thus, higher detuning frequencies may be used to fit Γ2* for diamond characterization. In addition, magnetometry curves, such as that shown in FIG. 62B, demonstrate that certain areas generate greater sensitivities. In particular, by taking the gradient of a two-dimensional FID surface plot, discreet optimal free precession intervals may be identified that present greater sensitivities, the best of which will be determined by Γ2*. FIG. 63B shows the gradient of the two-dimensional FID surface plot of FIG. 63 A. In FIG. 63B, for the particular Γ2 used (i.e., about 750 ns), operating at around 900 ns (indicated by area 2 of FIG. 63B) will yield the greatest sensitivity. However, shorter Γ2 will show better performance between about 400 ns and about 500 ns (indicated by area 1 of FIG. 63B), while longer Γ2* will show better performance at around 1400 ns (indicated by area 3 of FIG. 63B). These strong interference regions indicated by a plot such as that shown in FIG. 63B allow for the optimization of τ that will yield greater measurement sensitivity.

[00503] In addition, while the decay in the horizontal axis of FIG. 63B is characterized by Γ2, the decay in the vertical axis is characterized by the ratio of the resonant Rabi frequency ωτβε (described in more detail below) to the effective Rabi frequency a>eThe effective Rabi frequency may be defined by equation (a2) below:

(a2) [00504] Thus, the ratio of the resonant Rabi frequency and the effective Rabi frequency may be expressed in terms of the resonant Rabi frequency, as follows:

(a3) [00505] As shown in equation (a3) above, when the resonant Rabi frequency mres is much greater than the MW detuning Δ, the ratio of the resonant Rabi frequency to the effective Rabi frequency will be about equal to 1. The decay shown in the vertical axis of FIG. 63B may be partially controlled by RF excitation power. As will be described in greater detail below, as the RF excitation power increases, a greater resonant Rabi frequency may be realized, while also decreasing the percent change in the effective Rabi frequency due to detuning. Thus, according to certain embodiments, magnetometry measurements are operated in regions that are dominated by the resonant Rabi frequency (such that the ratio of equation (a3) is close to 1) in order to achieve maximum contrast.

Measurement Sequence [00506] Using the above observations, a general three-step approach may be used to obtain highly sensitive magnetometry measurements. In this general approach, a first step is performed to verify the resonant Rabi frequency o)res. In a second step, the inhomogeneous dephasing Γ2* of the system is measured. Finally, using the measurements obtained in the first and second steps, the parameter space of equation (al) is optimized and a highly sensitivity magnetometry measurement is performed. These three steps are described in more detail below.

Measuring the Resonant Rabi Frequency [00507] To verify the resonant Rabi frequency, first, a bias magnetic field using the magnetic field generator 6070 is applied to the system 6000 such that the outermost resonance of the fluorescence intensity response is separated, while the three remaining resonances for the other axes remain overlapping. Next, either a CW-CW sweep or a single π pulse sweep is applied to identify the resonance RF frequency that corresponds to the axis of interest (i.e., the outermost resonance). Then, while tuned to this resonance, a series of Rabi pulses is applied. FIG. 64 shows an example of a Rabi pulse sequence. As shown in FIG. 64, three periods of optical and RF excitation pulses are applied. First, a first optical excitation pulse 6410 is applied, which is followed by a RF excitation pulse 6420 (e.g., a MW pulse). The Rabi pulse sequence is then completed by a second optical excitation pulse 6430. During application of the series of Rabi pulses, the time interval in which the RF pulse is applied (shown as tau τ in FIG. 64, but this tau τ should be distinguished from the free precession interval τ in a Ramsey pulse sequence) is varied. During this process, a constant optical duty cycle is maintained to minimize thermal effects in the system. This may be achieved with the use of a variable “guard” window, shown as the period 6450 in FIG. 64, between the first optical pulse 6410 and the MW pulse 6420. The guard window 6450 helps to ensure that the first optical pulse 6410 is completely off by the time the MW pulse 6420 is applied, thus preventing any overlap between the two pulses and preventing the optical pulse from partially re-initializing the NV diamond material while the MW pulse 6420 is being applied.

[00508] After application of the Rabi pulses, the resonant Rabi frequency ωτβΞ is defined by the frequency of the resulting curve. FIG. 65 shows measured curves A-D after the application of the Rabi pulses using varying RF excitation power (e.g., MW power). As shown by the differences in the frequency of curves A-D, by increasing the MW power applied to the system 6000, the resonant Rabi frequency 0Jres obtained also increases. Thus, to obtain practical Rabi frequencies (e.g., greater than 5 MHz), substantial amounts of MW power should be used. In some embodiments, sufficient MW power may be applied to ensure that application of the pulses is kept short, while, at the same time, the MW power may be limited to avoid saturation. In certain embodiments, a power of about 10 watts may be applied. Depending on the RF excitation source 6030 used to apply the RF excitation, the necessary power requirements to achieve practical Rabi frequencies may be difficult to achieve. In certain embodiments, however, a small loop antenna (e.g., an antenna having a loop size of about 2 mm in diameter) may be used as the RF excitation source 6030. By applying a small loop antenna, a high MW power may be achieved while significantly reducing the required antenna power due to the ability to position the antenna in closer proximity to the NV diamond material 6020. Thus, the increase in MW power achieved by the small loop antenna allows for an increase in the resonant Rabi frequency o)res. The data obtained during this step of the measurement process is used to determine the π/2 pulse necessary to perform the Ramsey pulse sequence (described below). In this case, π may be defined as the first minimum of the Rabi curve obtained (e.g., curve D in FIG. 65).

Measuring T2* [00509] In a second step of the measurement process, using the π/2 pulse determined by the resonant Rabi frequency and the resonance location obtained during the first step above, measurements of the inhomogeneous dephasing Γ2* of the system are obtained. Measurements are performed similar to the Rabi measurements described above, except a Ramsey pulse sequence is used. As described above with reference to the Ramsey pulse sequence, tau τ denotes the free precession time interval in this step.

[00510] In estimating Γ2*, the detune frequency Δ is set to be relatively high, in certain embodiments. As noted above, larger detune frequencies cause higher fundamental frequencies (see, e.g., FIG. 63 A), thus allowing for greater contrast, making the data easier to fit. In some embodiments, the detune frequency Δ may be set to about 10 MHz. However, for relatively large Γ2*, smaller detune frequencies may be used. FIG. 62A shows one example of an FID curve that may be used to obtain Γ2*, where the detune frequency was set to about 10 MHz. By determining 7^ from an FID curve such as that shown in FIG. 62A, the optimal free precession time τ may be determined based on the strong interference regions discussed above with reference to FIG. 63B. In addition, in certain embodiments, a small range of x’s are also collected on either side of the optimally determined free precession time due to the theta term in equation (al).

Magnetometry Measurements [00511] In the final step of the measurement process, measurement of the fluorescence intensity response is performed using the parameters obtained in the above steps. As discussed above, the identified resonant Rabi frequency gives the duration of the MW π/2 pulse (used as RF excitation pulses 6120 and 6140), and the FID curve gives 7^, which is used to determine the region of optimal free precession time τ. It should be noted that, during this final step, in some embodiments, the optical pulse used for optical polarization of the system and the optical pulse used for measurement readout may be merged into one pulse during application of a series of Ramsey sequences.

[00512] In addition, in order to increase sensitivity, measurements made in a second per fixed measurement error may be increased in certain embodiments. Thus, to maximize sensitivity, the total length of a single measurement cycle should be minimized, which may be achieved through the use of higher optical powers of the optical excitation source 6010. Accordingly, given the above, in certain embodiments, the optical power of the optical excitation source 6010 may be set to about 1.25 W, the MW π/2 pulse may be applied for about 50 ns, the free precession time τ may be about 420 ns, and the optical excitation pulse duration may be about 50 ps. Moreover, “guard” windows may be employed before and after the MW π/2 pulses, which may be set to be about 2.28 ps and 20 ns in duration, respectively.

[00513] In conventional measurement processes, the curve in the intensity response is typically only measured once to obtain the slope and fine-tuned frequency, and additional measurements are only taken at the optimal detuning frequency, while the fluorescence signal is monitored. However, the system may experience drift caused by, for example, optical excitation heating (e.g., laser-induced heating) and/or strain, which can contribute to imprecision and error during the measurement process. Tracking a single spin resonance does not properly account for the translation in response curves due to thermal effects. Thus, according to some embodiments, to account for nonlinearities over a larger band of magnetic fields, data obtained from the measuring process is saved in real-time and sensitivity is determined offline to minimize time between measurements. In addition, magnetometry curves are collected on both the ms = +1 and ms = -1 spin states for the same NV symmetry axis. For example, in certain embodiments, RF excitation pulses during the Ramsey sequences may be alternatively applied at low resonance (i.e., resonance frequency of the ms = -1 spin state) and at high resonance (i.e., resonance frequency of the ms = +1 spin state) to obtain measurements associated with each of the spin states (ms = -1 and ms = +1 spin states). Thus, two magnetometry curves (e.g., FIG. 62B) may be obtained for both the positive and negative spin states. By applying the RF pulses at separate frequencies, translation due to temperature and/or strain effects may be compensated. The magnetic field measurements may be made using equations (a4) and (a5) below, where I represents the normalized intensity of the fluorescence (e.g., red) and mi and m2 represent the measurements taken for each of the ms = +1 and ms = -1 spin states for a given axis:

(a4) (a5) [00514] For measurements obtained on opposite slopes, plus is used in equation (a5). If the peaks of the ms = +1 and ms = -1 spin states translate, the intensity response will occur in opposite directions. If, on the other hand, the peaks separate outward due to a change in the magnetic field, then the intensity change will agree to yield the appropriate dB measurement. Thus, by obtaining measurements of the curves for both the ms = +1 and ms = -1 spin states for the same NV symmetry axis, changes due to temperature and changes due to the magnetic field may be separated. Accordingly, translation shifts due to temperature and/or strain effects may be accounted for, allowing for a more accurate calculation of the magnetic field contribution on the system.

Signal Processing [00515] Processing may be performed on the raw data obtained to acquire clean images of the measurements obtained during each of the steps described above. FIG. 66 shows an example of a raw pulse data segment that may be obtained during a given measurement cycle. Theoretically, the signal is defined as the first 300 ns of an optical excitation pulse. However, this definition applies at optical power densities that are near saturation. As optical power density decreases from saturation, the useful part of the signal may extend further in time. Currently, in conventional processing methods, the end of the pulse, when the system has been polarized, is referenced in order to account for power fluctuations in the optical excitation source (e.g., the laser). This is shown in FIG. 66, where the signal may be obtained using a first reference window or period defined by C minus a signal window or period defined by B (i.e., signal = C — B), which are both referenced after the MW pulse. According to certain embodiments, however, in order to increase sensitivity, the reference may be extended to include a second reference window or period defined by A before the microwave pulse (i.e., signal =

— B). The samples within the windows or periods (i.e., A, B, and C) may be averaged to obtain a mean value of the signal contained within the respective window or period.

Furthermore, in some embodiments, the value of the windows or periods (e.g., signal window B) may be determined using a weighted mean. In addition, in certain embodiments, the first and second reference windows are equally spaced from the signal window, as shown in FIG. 66.

This extension of referencing allows for better estimation of the optical excitation power during the acquisition of the signal and an overall increase in sensitivity of the system.

[00516] DIAMOND NITROGEN VACANCY SENSOR WITH COMMON RF AND MAGNETIC FIELDS GENERATOR

[00517] FIG. 67 is a schematic illustrating a portion of a DNV sensor with a coil assembly in accordance with some illustrative implementations. The magnetic sensor shown in Figure 6 used a single RF excitation source 630 and a bias magnet 670. The DNV sensor illustrated in Figure 7 uses six separate RF elements that also provide the bias field that is provided the bias magnet 670 in Figure 6. Accordingly, in various implementations, the DNV sensor shown in Figure 67 does not require a separate bias magnetic. Figures 67 - 73 illustrate various components of the DNV sensor.

[00518] In Figure 67, the portion of the illustrated DNV sensor includes a heatsink 6702 that can connect to the rest of the DNV sensor via a mounting clamp. Not shown is a light element, such as a laser or LED that is located within or near the heatsink 6702. Light from the light element travels through a lens tube 6706 through a focusing lens tube 6718 and through a coil assembly 6716 that includes the NV diamond. Light passes into the coil assembly 6716 through the NV diamond and exits the coil assembly. Light that exits the coil assembly passes through a red filter to a photo sensor assembly 6714. The coil assembly 6716, red filter, and photo sensor can all be housed in a lens tube 6710 that can be coupled to lens tube 6718 via a lens tube coupler 6708. A lens tube rotation mount 6712 allows a rotation adjustment element to be attached that allows the coil assembly to be rotated in relation to the light element.

[00519] Figure 68 is a schematic illustrating a cross section of a portion of a DNV sensor with a coil assembly in accordance with some illustrative implementations. The portion of the DNV sensor that is illustrated contains the coil assembly 6816 and the photo sensor 6820. The coil assembly 6816 includes six RF elements. Each RF element has an RF mount that can be used to connect an RF cable 6830. Thus, each RF element can have its own RF feed. In various implementations, the each RF element is fed a unique RF signal. In other implementations, subcombinations of the RF elements receive the same RF feed signal. For example, groups of two or three RF elements can receive the same RF feed signal. Various connectors can be used to connect an RF cable 6830 to the RF elements, such as a right angle connector 6832. The coil assembly 6816, red filter 6826, EMI glass 6824, and photo sensor mounting plate can be held in place using retaining rings 6802. A photo sensor 6820 can be secured to the photo sensor mounting plate 6822, which can be used to locate the photo sensor 6820 in the path of light that exits the coil assembly 6816.

[00520] Figure 70 is a cross section illustrating a coil assembly in accordance with some illustrative implementations. In this illustration, the light path 7030 is shown. The light path allows for light from the lighting element to pass through the coil assembly and through the NV diamond 7040. Light exits the NV diamond and proceeds out of the coil assembly through the light path 7030.

[00521] The coil assembly includes four RF elements 7002 and two top and bottom elements 7020. The NV diamond 7040 is held in place via a diamond plug 7004 that holds the diamond in the mounting block 7006. The RF elements can be held together using various means such as element mounting screws 7032. The six total RF elements can be seen in Figures 69A and 69B that illustrate a coil assembly in accordance with some illustrative implementations. Four side RF elements 6902 are shown along with two top and bottom RF elements 6920. Each RF element is attached to a center mounting block 6904. Attachment mechanisms such as screws 6932 can be used to attach the RF elements to the mounting block.

In the illustrated implementation, a light injection hole 6930 is the bottom RF element and the light exit hole 6970 is in the top RF element. Accordingly, in this implementation light passes through the coil assembly and the diamond in a straight path. In one implementation, the light enters a face of the NV diamond and exits through another face of the NV diamond. As described below, in other implementation the light path through the coil assembly is not straight and may take on multiple paths of egress.

[00522] Figure 71 is a schematic illustrating a side element 7100 of a coil assembly in accordance with some illustrative implementations. The side element 7100 can include a middle mounting hole and one other mounting hole. In this implementation, there would be side elements that had different mounting hole configurations. As shown in Figure 71, the side element 7100 has three mounting holes, but not all mounting holes are required to be used. In one implementation, the middle mounting hole and one of the remaining two mounting holes are used, but all three mounting holes are not used. Each side element 7100 includes an RF connector 7102 that is used to provide the RF feed signal to the side element.

[00523] Figure 72 is a schematic illustrating a top or bottom element 7200 of a coil assembly in accordance with some illustrative implementations. Similar to the side element 7100, the top or bottom element 7200 includes an RF connector 7202 for receiving an RF feed signal. The top or bottom element 7200, however, has only two mounting holes 7204. The three hole is a light path portion 7230 that allows for light to enter or exit the coil assembly.

[00524] Figure 73 is a schematic illustrating a center mounting block 7300 of a coil assembly in accordance with some illustrative implementations. The NV diamond is located within the mounting block 7300. In one implementation, a diamond plug can be used to hold the NV diamond. The mounting block 7300 can include a diamond mounting location that provides alignment of the NV diamond. For example, the mounting block 7300 can include a recess that fits the NV diamond. Once positioned, the diamond plug can be inserted into the mounting block 7300 to hold the diamond in place.

[00525] Figures 74-77 illustrate another implementation. Figure 74 is a cross section illustrating of a portion of a DNV sensor with a coil assembly in accordance with some illustrative implementations. A coil assembly 7416 holds an NV diamond within an NV diamond sensor. The coil assembly 7416 can include six RF elements, four side elements and two top and bottom elements (shown in Figures 75-77). RF cables 7430 can connect to the RF elements via RF connections 7432. The RF cables 7430 are used to provide an RF signal to one or more of the RF elements. The RF signal can be different for each RF element or subsets of the RF elements can receive different RF signals. These RF feed signals are used by the RF elements to provide a uniform microwave RF signal to the NV diamond. In addition, the arrangement of the RF elements allows the RF elements to also provide the magnetic bias field to the NV diamond. In the illustrated implementation, light enters and exits through the top and bottom elements. Light that exits the NV diamond can pass through a red filter 7426 and through a light pipe 7450 that is located within an attenuator 7440. In various implementations, at least a portion of the light pipe 7450 is located within the attenuator 7440. Such a configuration allows the photo-sensing array 7420 to be positioned closer to the NV diamond and remain unaffected by the EMI of the sensor. Further description of the benefits of housing a portion of the light pipe within an attenuator is described in U.S. Patent Application No. / ,_, entitled “Magnetometer with Light Pipe,” filed on the same day as this application, the contents of which are hereby incorporated by reference. Retaining rings 7402 can be used to hold the various elements together and in position.

[00526] Figure 75 is a schematic illustrating a coil assembly in accordance with some illustrative implementations. Figure 76 is a schematic illustrating a cross section of a coil assembly in accordance with some illustrative implementations. The coil assembly includes two bottom or top RF elements 7506 and 7606. In the illustrated implementation, the top or bottom RF elements are circular and are larger compared to the side elements 7502 and 7602. In between the top or bottom elements are the four side elements 7502 and 7602. Figure 77 is a schematic illustrating a side element of a coil assembly in accordance with some illustrative implementations. The side element has an RF connector 7702 used to provide a feed RF signal to the RF element. The side RF elements do not include any mounting holes as the side RF elements can be held into position by the top and bottom RF elements. In various implementations, each of the RF elements can include multiple stacked spiral antenna coils.

These stacked coils can occupy a small footprint and can provide the needed microwave RF field in such that the RF field is uniform over the NV diamond. Additional details regarding RF elements and RF circuit boards that contain RF elements are described in U.S. Patent Application

No. _/_,_, entitled “DIAMOND NITROGEN VACANCY SENSOR WITH DUAL RF SOURCES,” filed on the same day as this application, the contents of which are hereby incorporated by reference. In various implementations, each RF side element and top and bottom RF elements can include an RF element or an RF circuit board.

[00527] The NV diamond 7622 is located within the six RF elements. The RF elements can be held together by mounting screws 7510 and 7610. A light injection portion 7504 of the top RF element allows light to enter the coil assembly and enter the NV diamond. The bottom portion includes a corresponding light egress portion 7620. The NV diamond can fit within a mounting block 7608 and be held in position via a diamond plug 7624.

[00528] Figures 78-84 illustrate another implementation. In the illustrated implementation, light enters the NV diamond through an edge of the NV diamond and exits through multiple faces of the NV diamond. How light enters and exits the NV diamond is based upon the orientation of the NV diamond relative to the light source. Thus, in various implementations the NV diamond can be repositioned to allow light to enter and exit from edges, faces, and/or both edges and faces.

[00529] Figure 78 is a schematic illustrating a portion of a DNV sensor with a coil assembly in accordance with some illustrative implementations. Similar to other implementations, the DNV sensor includes a light source heatsink 7802 and 7902, a mounting clamp 7804 for the heatsink 7802, a lens tube 7806, a focusing lens tube 7818, a coil assembly 7816 located, and red filters and photo sensor assemblies 7814, and a lens tube rotation mount 7812 and 7912. Figure 79 is a schematic illustrating a cross section of a portion of a DNV sensor with a coil assembly in accordance with some illustrative implementations. In this implementation, the light source is an LED 7906. In other implementations, other light sources, such as a laser, can be used. A thermal electric cooler 7904 can be used to provide cooling for the LED 7906. Light from the LED 7906 can be focused using lens 7918. The focused light enters the NV diamond that is located within the coil assembly 7916.

[00530] Figure 80 is a schematic illustrating a cross section of a portion of a DNV sensor with a coil assembly in accordance with some illustrative implementations. In this figure, the NV diamond 8040 within the coil assembly can be seen. Light enters the edge of the NV diamond in this implementation and exits the NV diamond 8040 from two faces of the NV diamond 8040. The light the exits the NV diamond 8040 travels one of two light pipes 7914. In various implementations, at least a portion of the light pipe is located within an attenuator. The NV diamond 8040 can be held in place within the coil assembly via center mounting blocks 8050. The mounting blocks and the coil assembly can be held in place using retaining rings 8052. RF cables 8030 connect to the RF elements via RF connectors 8032 to provide an RF feed signal to the RF elements as described in greater detail below.

[00531] Figure 81 is a schematic illustrating a coil assembly in accordance with some illustrative implementations. Figure 82 is a schematic illustrating a cross section of a coil assembly in accordance with some illustrative implementations. Figure 81 shows four side elements 8014 and 8242 located between the top and bottom RF elements 8112 and 8212. The center mounting blocks 8108 and 8208 and retaining plate 8106 and 8206 are also shown. As describe above, light enters the NV diamond 8240 at an edge. The light reaches the NV diamond via a light injection opening 8101 and 8202. Light exits the NV diamond 8240 substantially orthogonal to the ingress path through two light exit holes 8110. A second light exit hole is opposite of the illustrated light exit hole 8110. In Figure 82, the second light exit hold is behind the NV diamond 8240.

[00532] Figure 83 is a schematic illustrating a side element of a coil assembly in accordance with some illustrative implementations. The individual side element includes an RF connector 8304 and a light egress portion 8302. The side element, however, does not include any attachment holes. Rather, the side elements can be held in place within the coil assembly using the top and bottom elements as illustrated in Figures 84A and 84B.

[00533] Figures 84A and 84B are schematics illustrating top and bottom elements of a coil assembly in accordance with some illustrative implementations. The top element includes slots 8406 for aligning and holding into position the four RF side elements. The light injection hole 8404 is also shown. RF connectors 8404 located on both the top RF element and the bottom RF element allow for separate RF feeds to be separately applied to the top and bottom RF elements.

[00534] GENERAL PURPOSE REMOVAL OF GEOMAGNETIC NOISE

[00535] Various aspects of the subject technology provide methods and systems for general purpose removal of geomagnetic noise. The subject solution combines the use of an array (e.g., 1-D or 2-D) of highly sensitive vector magnetic sensors with proper transformation means and signal processing to separate the broadly-spatially-correlated Pc and Pi noise from the local anomalies that affect fewer sensors of a spatially distributed array of DNV sensors. The vector magnetic sensors of the subject technology are large enough and spaced densely enough such that the magnetic signal of interest (SOI) is detected by at least one sensor but is below the target noise floor for many of the other sensors. The proper transformation means can achieve transforming the sensor measurements to a common coordinate system by transforming each element of an array of measured magnetic field values to provide an array of transformed magnetic field values. The signal processing includes signal processing of the spatially distributed array of sensors.

[00536] Geomagnetic noise [00537] Geomagnetic noise that is of considerable significance is that due to the solar wind impinging on the exoatmosphere. This noise can be decomposed into diurnal variations (slow daily variations due to the orientation of the earth relative to the sun) and what are termed “Pc and Pi” noise. The Pc and Pi noise are the most problematic in many potential applications, as they vary in time scales that are similar to the magnetic signals that one may wish to measure (signals resulting from some object in motion relative to a magnetic sensor, either because the object is moving and the sensor is stationary, or because the object is stationary and the sensor is being moved, or some combination). It is thought that the Pc and Pi noise, together, span the frequency range of 0.01 Hz and 5 Hz, with a spectrum shape proportional to 1/f (f is frequency) in this band.

[00538] The nature of the Pc and Pi noise may be investigated by comparing generated model Pc and Pi noise to that of empirical data. This model Pc and Pi noise may be generated, for example, by passing white Gaussian noise through a linear filter with this shape and steep rolloff above and below this passband. For amplitude, empirical data was used from: J. Watermann and J. Lam, “Distributions of Magnetic Field Variations, Differences, and Residuals,” SACLANTCEN, San Batrolomeo, IT, Tech. Rep. SR-304, Feb. 1999 (“SACLANTCEN”), which measures peak-to-peak values over time windows of different lengths, averaged over months. The noise amplitude of the model data is adjusted to have comparable peak-to-peak statistics. The comparison is shown in FIG. 85, where the geomagnetic noise model compares well with empirical data.

[00539] The SACLANTCEN paper also suggests that the geomagnetic noise is spatially highly correlated over tens of kilometers. Other sources discuss the Pc and Pi noise as originating at an altitude of about 100 km, affirming that it is reasonable to expect high correlation over distances greater than 10 km when measured on the earth surface or undersea.

[00540] Signal of interest [00541] FIG. 86 illustrates a signal of interest due to a distortion in the magnetic field in the Z-direction by an unmanned underwater vehicle (UUV) for magnetic field over time as measured by a single magnetic sensor. FIG. 86 illustrates the signal of interest without noise and a measurement of the signal of interest including noise. As can be seen, the signal of interest is overwhelmed by the noise.

[00542] FIGs. 87A-87C illustrate the signal of interest due to a distortion in the magnetic field in the Z-direction by an unmanned underwater vehicle (UUV) for magnetic field at three different times as measured by a two-dimensional array of sensors, to provide an array of measured magnetic field values, on the sea floor. As can be seen, the noise appears fairly flat over the area shown, with the excepton of a hill-valley pair which is the signal of interest (magnetic field distortion from presence of a ferrous metal object, the UUV). The array used for the dataset is a 3 l-by-31 sensor array spaced at 100m, such that the center is the 16 (row), 16 (column) sensor.

[00543] Removal of geomagnetic noise [00544] In some aspects of the present technology, methods and configurations for general purpose removal of geomagnetic noise are disclosed. The subject technology combines precision vector magnetometers with a large and dense array of sensors, a means of establishing a common coordinate system, high pass time domain filtering, and noise removal exploiting spatial correlation of noise. The large and dense array of sensors is sufficiently large such that many sensors are unaffected by a signal of interest and spaced closely enough such that the signal of interest is detected by at least one sensor when the signal is present. In some implementations, the sensor array may include 1-D (one-dimensional) or 2-D (twodimensional) array of many precision vector magnetometers. High pass time-domain filtering can remove very slow variations on the order of many hours or longer.

[00545] For ease of description, let S be the signal defined as the local magnetic field variation of interest, which is to be measured, and let F be the interest floor chosen to be a value lower than the amplitude of S to be used in the definition of signals that are too small to be of interest. Let Rmax be the maximum influence region of S, defined as maximum size and shape of the region (1-D or 2-D) in which the amplitude of S may be greater than F. Let N be the vector environmental noise for which the time variations of the noise may be large compared to S, but at each time sample are spatially correlated such that the variation is much less than F over a distance more than twice the diameter of Rmax. Using the above definitions, the vector magnetic sensor of the subject technology are of high precision relative to F such that the sensor noise is negligible as compared to F. The array (1-D or 2-D) of these sensors is dense enough such that when the variation of interest is present, S is greater than F for at least one sensor and large enough relative to Rmax such that for most of the sensors, S is less than F. The means of establishing a common coordinate system can measure the orientation of the sensors relative to the local earth coordinate system so as to achieve a common coordinate system among the sensors. A spatial-domain common-mode rejection algorithm (CMRA) processes each time sample of the array measurements and produces an array of values preserving local variations greater than F, while reducing residual errors from N to amplitude below F.

[00546] In one or more implementations, the magnetic sensor is a DNV sensor. The means of measurement of the orientation of the sensor can be the measurement of the earth’s local magnetic field as one reference direction, and an inclinometer (gravity) vector measurement as a second reference direction. In some aspects, the CMRA includes subtraction of the median value of the sensor array at each point in time. The CMRA can further include the combination of the identification of a region of interest where S may be present, a noise estimation using the measurements outside of the region of interest, and subtraction of the estimated noise. The identification of a region of interest may be performed either by using the difference of the measured value from the median value exceeding a chosen threshold, or the spatial gradient of the measured value exceeding a chosen threshold. The noise estimation can be performed by fitting the measurements with a curve such as a constant (e.g., the average of the measurements), a line (e.g., in the case of a 1-D array), a plane (e.g., in the case of a 2-D array), or a spline. In some implementations, the noise estimation can include a Kriging approach to estimate the noise in the region of interest from the measured values outside of the region of interest.

[00547] Magnetic sensor array system [00548] FIG. 88 illustrates a magnetic sensor array system 8800 according to an embodiment of the invention. The system includes a controller 8810 and a magnetic sensor array 8830, which includes a number of magnetic sensors 8832. The spacing being adjacent sensors 8832 may be s, for example. While FIG. 88 illustrates the magnetic sensors 8832 to be arranged in a two-dimensional array, the magnetic sensors 8832 may be arranged in a onedimensional array or in some other dimension. Further, while FIG. 88 illustrates a 4 by 3 array of sensors 8832 for simplicity, in general the array may be much larger, or may be smaller.

[00549] The controller 8810 receives magnetic field signals from each of the magnetic sensors 8832, where the magnetic field signals are indicative of the magnetic field measured at each of the magnetic sensors 8832. Thus, the controller 8810 receives an array of magnetic field values. The controller 8810 may include a processor 8812 and a memory 8814. The magnetic field signals received by the controller 8810 may be stored in the memory 8814 as data. The memory 8814 may further store instructions which are executed by the processor to allow the controller 8810 to perform various data processing operations, such as establishing a common coordinate system, high pass time domain filtering, and noise removal exploiting spatially coordinated noise, as discussed further below. The memory 8814 may include a nontransitory computer readable medium to store the instructions and data.

[00550] While FIG. 88 illustrates a single processor 8812 and a single memory 8814, in general the controller 8810 may include more than one processor 8812 to perform various functions, and may include more than one memory. Further the controller 8810 may include subcontrollers arranged in a distributed manner.

[00551] The sensors 8832 may be DNV sensors, for example, or other magnetic sensors such as Hall effect sensors.

[00552] Common coordinate system for magnetic sensors [00553] The magnetic fields measured by each of the magnetic sensors may be transformed to a common coordinate system which is common to all of the magnetic sensors. Thus, the measured magnetic field values are transformed to an array of transformed magnetic field values. FIGs. 89A and 89B illustrate a common coordinate system, and coordinate system corresponding to one of the magnetic sensors, respectively. As an alternative to transforming to a common coordinate system, the sensors may be arranged such that they are fixed relative to each other such that they are initially in a common coordinate system. This could be accomplished by fixing the sensors in a rigid material, for example.

[00554] In the coordinate system, the Z axis is considered to be “down,” that is, the direction of the gravity vector. In general, while there may be extremely slight variations in the direction of the gravity vector for the different elements of the sensor array, these variations will be extremely small in comparison to the gravity sensor errors introduced for the sensor error model, and thus can be considered included in the sensor error model. The X axis is considered to be perpendicular to the Z axis such that the local magnetic north vector is in the X-Z plane. Y is considered to be perpendicular to X and Z thus providing a right-hand coordinate system, where Y is pointed nearly east.

[00555] FIG. 90 illustrates an orientation sensor 9000 attached to a magnetic field sensor 8832. Each of the magnetic field sensor 8832 may have a corresponding orientation sensor 9000, which measures the orientation of magnetic field sensor 8832 relative to one or more directions, such as the Z-direction, for the common coordinate system. The orientation sensor 9000 aids in achieving a common coordinate system for the data from all of the sensors 8832. The orientation sensor 9000 may be a gravity sensor, which is affixed to a corresponding one of the sensors 8832. The orientation sensor 9000 is aligned with its corresponding sensor 8832 so as to be in a same coordinate system.

[00556] It is assumed that the sensors 8832 are initially scattered at random orientations. Then, any vector V in the X, Y, Z general coordinate system will be measured in the sensor coordinate system of a sensor as VM = RV where R is a unitary rotation matrix for the particular sensor 8832. In general, for the sensor arranged in the i,j position in the array, R could be designated as R1,7 to denote the rotation matrix associated with the sensor in the i, j position since it will be different for each i, j. In discussing a single sensor the i, j notation may be omitted for simplicity.

[00557] The columns of R are the directions the X, Y, and Z components appear in the sensor coordinate system. To convert the sensor measurements to the X, Y, Z common coordinate system, one simply correlates with R. That is, V = RTVM, wherein, RTR = /, the identity matrix.

[00558] Converting the magnetic measurements of each magnetic sensor 8832 to a common coordinate system is as follows. For each sensor, measure R as a coordinate system calibration step. This may be achieved partly by using a gravity sensor as the orientation sensor 9000, for example. Alternatively, the orientation may be taken based on detection of the orientation of the stars. Then take the product of magnetic measurements with the transpose of the rotation matrix, RT, to place the magnetic measurements in the X, Y, Z common coordinate system.

[00559] The rotation matrix R may be estimated as follows. As stated, the third column of R is the vector direction in a sensor coordinate system that would result from an input in the Z direction. The estimate of the Z direction in sensor coordinates may be denoted as Z, thus the estimated R, denoted R, has as its third column, Z. Likewise, the first and second columns of R may be denoted as X and Ϋ respectively. Thus, determining the estimated R is performed by estimating the columns of R, being X, Ϋ and Z.

[00560] The Z value may be simply taken as the measurement of Z from the orientation sensor 9000, which may be a gravity sensor. The measurement of Z from a gravity sensor will be the true value of Z plus a rotation error in the sensor. A reasonable bound on a rotation error for existing cost-effective gravity sensors is 0.01 degrees.

[00561] The Xvalue may be calculated by taking the magnetic measurement of a sensor 8832, which is dominated by the earth’s local magnetic field, and removing the component in the Z direction and then normalizing, using routine linear algebra. This will closely approximate X, with minor errors due to the very small variations in magnetic north over the array, and with small geomagnetic noise and magnetic sensor noise, and the errors in Z. Ϋ may then be calculated with a standard cross-product calculation between X and Z.

[00562] The accuracy of the transformation of the magnetic field measurement to a common coordinate system may be estimated as follows.

[00563] As an initial step, all of the sensors are independently randomly orientated, with the following process: For each sensor: (1) generate an axis of rotation by selecting a random vector with a uniform distribution over the unit sphere, (2) generate an angle of rotation by selecting a random angle uniformly from

and (3) create a random rotation matrix for the sensor based on the selected axis of rotation and angle of rotation by using well-known linear algebra techniques, such as the Rodrigues' rotation formula, for example. This random rotation provides the true value for Rl,i for each i,j sensor. The rotation is then applied to the magnetic field dataset of the sensor, producing the dataset in the non-aligned individual sensor coordinates.

[00564] For each magnetic sensor, Rl,i for each i, j was calculated separately, with the following imperfection including: (1) a gravity sensor rotational error of about 0.01 degrees, unique for each sensor, where the error was simulated by: (a) randomly picking a rotation error from a uniform distribution over [-0.01 degrees, 0.01 degrees], (b) rotating a unit vector lined up with the Z-Axis towards the Y-Axis by the selected rotation error to form Z’, (c) randomly picking a second rotation angle uniformly from [0, 2π], and (d) rotating Z’ about the original Z-axis by the selected second rotation angle, and (2) a single time sample of the modeled geomagnetic noise and magnetic sensor noise. The single time sample was provided such that the value of the earth’s magnetic field (magnetic north) was based on a location in the ocean in the vicinity of New York City. At this latitude, magnetic north had a significant inclination.

In X, Y, Z coordinates, the earth magnetic field vector used was

micro Tesla.

[00565] For each sensor, the transpose of Rl,i was applied to place the measurements in the common X, Y, Z coordinate system. That is the data used below for all of the common mode rejection algorithms. Further, for the common mode rejection algorithms that follow, a (time/freq domain) high-pass filter is applied to the array of measured magnetic field values remove variations that are very slow (e.g. nearly constant over hours) and therefore the large magnetic north component is absent. Here, for coordinate system calibration, the unfiltered magnetic measurement is used because magnetic north is of interest in establishing the coordinates.

[00566] As a final view of the accuracy of the common coordinates, the imperfection of the inverse was measured by taking E = [Rl,j]T[RlJ] — / for all i, j. The induced 2-norm of E (maximum singular value) across the array is typically around 0.0004, which is very small compared to 1. Hence, the approximate R inverse is quite accurate.

[00567] In summary, applying random sensor rotations and the approximate correction to a common coordinate system, the true high-passed (DC removed) magnetic field data

DjJ (t) in the X, Y, Z coordinate system is provided and is then converted to sensor measurements, and then the sensor measurements are transformed (with imperfections) to a common coordinate system dataset, which in the true X, Y, Z coordinate system is Z)lJ(t) = [RL,i]T[R l^]DLtJ (t).

[00568] Common Mode Rejection Algorithm to recover signal of interest [00569] Figures 91A-91I illustrate the array of measured magnetic field values including the magnetic signal of interest without noise in a scenario where one UUV is travelling past the array of sensors, and Figures 93 A-93I illustrate the signal of interest with two UUVs passing at different depths and in different directions. FIGs. 91A-91C illustrate the magnetic field measurement component along the X-direction, Y-direction and Z-direction, respectively, at a time of 500 seconds. FIGs. 91D-91F illustrate the magnetic field measurement component along the X-direction, Y-direction and Z-direction, respectively, at a time of 1000 seconds. FIGs. 91G-91I illustrate the magnetic field measurement component along the X-direction, Y-direction and Z-direction, respectively, at a time of 1500 seconds. FIGs. 93A-93I correspond to FIGs. 91A-91I, respectively, but for the case of two UUVs.

These are the signals of interest to be recovered when all sensor imperfections and noise are included.

[00570] In recovering the signal of interest, first all sources of noise and sensor error are included in the magnetic field measurement data set in a manner as discussed above. The algorithms to produce a common coordinate system are employed, and various CMRA are then applied. To visualize the effectiveness of the results, the results at a single sensor as time evolves is shown where the left plot shows the measurement at that sensor, and the noise-free signal of interest (see FIG. 93 A, for example). It is clear from the plot that the signal is not visible in the measurement without the geomagnetic noise removal. The middle plot (see FIG. 93B, for example) shows the result at the same sensor, which plot shows the perfect noise-free signal of interest, and the output of the CMRA after noise removal. For all of the CMRA algorithms, the reconstruction looks nearly perfect in the center plot. The right plot (see FIG. 93C, for example), however shows the difference in the two lines (noise free and reconstructed) of the center plot, on a different scale, to show that the reconstruction is not actually perfect. For ease of illustration, only the results of the magnetic field along the X-direction is shown in the left, middle and right plots, where the magnetic field of course may be reconstructed additionally in the Y-direction and the Z-direction. The actual results in practice would depend on the specific noise levels and other errors.

[00571] Median subtraction algorithm [00572] According to the Median Subtraction Algorithm, the median value of the magnetic field for all of the sensors of the array is determined for each of the X, Y, and Z coordinates separately, and the median value is then subtracted from the magnetic field dataset. Thus, the median value of the magnetic field value is taken as an estimate of the spatially correlated background noise and subtracted from the transformed magnetic field values to provide noise removed magnetic field values. Because the noise is spatially highly correlated and because the signal of interest is significant in less than half of the array, the median value is a reasonable measurement of the geomagnetic noise. Figures 93A-93C show the results for the Median Subtraction approach, where FIG. 93 A shows the magnetic measurement at one of the sensors, and the noise-free signal of interest, over time, FIG. 93B shows the result at the same sensor after noise removal, and the noise-free signal of interest, and FIG. 93C shows the difference in the two lines (noise free and reconstructed) of FIG. 93B, on a different scale. Figures 94A-94C shows the magnetic field including the signal of interest in the X-direction for the array at times of 500, 1000 and 1500 seconds, respectively, which demonstrates an excellent fit when compared to the noise free signal shown in FIGs. 91 A, 91D and 91G, respectively.

[00573] Spatially correlated noise in region of interest [00574] The spatially correlated noise in the region of interest, where the region of interest provides the signal of interest, may be estimated, and subtracted from the magnetic field measurement in the region of interest. There are multiple approaches to estimating the spatially correlated noise, and examples are provided below. In general, the spacing of the sensors and the size of the array of sensors is such that some of the sensors 8832 are not in the region of interest. The fraction of the sensors which are outside the region of interest may be > 50%, for example.

[00575] For each of the examples, the following steps are taken. First, a “region of interest” is established, where the region of interest are those magnetic sensors where there appears to be a signal of interest because the magnetic measurements show local deviation from the spatially correlated noise by more than a predetermined threshold. In the region of interest the array elements where the signal of interest exists are adjacent to each other.

Second, the region of interest is excluded from the region where the rest of the measurement are performed (the remaining magnetic sensors which are not part of the region of interest) to provide a remaining array of transformed magnetic field values, and the rest of the measurements are used to estimate the geomagnetic noise. Finally, the estimated geomagnetic noise is subtracted from the entire region (the region of interest plus the remaining region) covered by the magnetic sensor array (all of the magnetic sensors) including the signal of interest.

[00576] One method for identifying the signal of interest is as follows. The median measured magnetic field is subtracted across the array from each magnetic sensor, and then a predetermined amplitude threshold (such as .01 nT in these examples) is applied. Any magnetic sensor values above the threshold are assumed to be signals of interest in the region of interest.

[00577] Optionally, the region of interest may be expanded slightly using expansion techniques. Because magnetic field variations do not change abruptly, the region of interest may be expanded. For example, the region of interest may be expanded using a set closing algorithm, based on dilation followed by erosion, using standard morphological image processing techniques and then taking the convex hull of the resulting region.

[00578] Figures 95A-95C shows the resulting regions of interest in an example for the magnetic field component in the X-direction at 500, 1000, and 1500 seconds, respectively. In each case, the lighter color region is the “core” region of interest, i.e. the values for which the measurements deviate from the array median enough to exceed the threshold. The darker color regions are the additional sensors that are included in the region of interest as a result of set closing and convex hulling of the region. As an alternative to set closing and convex hulling of the region, the region of interest could be expanded by taking the union of the regions according to the magnetic field components in the X-direction, Y-direction and Z-direction, or, alternatively use the 2-norm of the vector value in the thresholding step.

[00579] Once the region of interest is identified, it is removed, and then the rest of the data is fit, such as, for example, by fitting to a plane, or fitting to a quadratic spline. This gives a geomagnetic noise estimate that can be used in the entire region including the identified region of interest. As an alternative to fitting to a plane or aquadratic spline, a Kriging technique could be applied to the data with region of interest removed, to produce an estimate of the noise in the region of interest.

[00580] FIGs. 96A, 96B and 96C illustrate a fit of a plane to the data for the magnetic field component in the X-direction, where FIGs. 96A, 96B and 96C correspond to times of 500, 1000 and 1500 seconds. In FIGs. 96A, 96B and 96C, the fit plane is the meshed sheet, and the specific sensor measurements are the dots. The dots obscure the plane to some extent, but in all cases the plane is a reasonably good fit. There are a few points near the region of interest that are not as close to the plane. This is because they are affected by the signal of interest but at a level below the thresholding, and are also outside of the set closing and convex hulling which increases the region of interest. For this example, there are enough other sensor elements that the noise estimation is effective in spite of those exceptional sensor measurements. A greater dilation of the region of interest could be employed, but it is not necessary in this example.

[00581] FIGs. 97A, 97B and 97C illustrate the results for the X-direction magnetic field component obtained by subtracting the planar estimate of the noise, where FIG. 97A shows the magnetic measurement at one of the sensors, and the noise-free signal of interest, over time, FIG. 97B shows the result at the same sensor after noise removal, and the noise-free signal of interest, and FIG. 97C shows the difference in the two lines (noise free and reconstructed) of the FIG. 97B, on a different scale. As can be seen, the noise removal works well.

[00582] FIGs. 98A, 98B and 98C illustrate a fit of a quadratic spline to the data for the magnetic field component in the X-direction, where 98A, 98B and 98C correspond to times of 500, 1000 and 1500 seconds. In FIGs. 98A, 98B and 98C, the fit quadratic spline is the meshed sheet, and the specific sensor measurements are the dots.

[00583] FIGs. 99A, 99B and 99C illustrate the results for the X-direction magnetic field component obtained by subtracting the quadratic spline estimate of the noise, where FIG. 99A shows the magnetic measurement at one of the sensors, and the noise-free signal of interest, over time, FIG. 99B shows the result at the same sensor after noise removal, and the noise-free signal of interest, and FIG. 99C shows the difference in the two lines (noise free and reconstructed) of the FIG. 99B, on a different scale.

[00584] Example with two UUVs [00585] An example with two UUVs is now described. As described with respect to FIGs. 100A, 100B and 100C, two regions of interest corresponding respectively to the two UUVs are first identified in a manner similar to that described above with respect to a single UUV. The regions of interest are then expanded using a set closing algorithm, based on dilation followed by erosion, using standard morphological image processing techniques and then taking the convex hull of the resulting region.

[00586] Figures 100A-100C shows the resulting regions of interest in an example for the magnetic field component in the X-direction at 500, 1000, and 1500 seconds, respectively. In each case, the lighter color region is the “core” region of interest, i.e. the values for which the measurements deviate from the array median enough to exceed the threshold. The darker color regions are the additional sensors that are included in the region of interest as a result of set closing and convex hulling of the region. As can be seen, two regions of interest a identified, each one corresponding to a different one of the two UUVs. First as can be seen, the regions of interest are first separated as shown in FIG. 100 A, and then overlap in FIG. 100B, and then are separated again in FIG. 100C, suggesting that the two UUVs are moving so that one passes over the other.

[00587] Once the regions of interest are identified, they are removed, and then the rest of the data is fit, such as, for example, by fitting to a plane, or fitting to a quadratic spline. This gives a geomagnetic noise estimate that can be used in the entire region including the identified region of interest. As an alternative to fitting to a plane or aquadratic spline, a Kriging technique could be applied to the data with region of interest removed, to produce an estimate of the noise in the region of interest.

[00588] FIGs. 101 A, 101B and 101C illustrate, for the two UUV case, a fit of a quadratic spline to the data for the magnetic field component in the X-direction, where 101 A, 101B and 101C correspond to times of 500, 1000 and 1500 seconds. In FIGs. 101A, 101B and 101C, the fit quadratic spline is the meshed sheet, and the specific sensor measurements are the dots.

[00589] FIGs. 102A, 102B and 102C illustrate, for the two UUV case, the results for the X-direction magnetic field component obtained by subtracting the quadratic spline estimate of the noise, where FIG. 102A shows the magnetic measurement at one of the sensors, and the noise-free signal of interest, over time, FIG. 102B shows the result at the same sensor after noise removal, and the noise-free signal of interest, and FIG. 102C shows the difference in the two lines (noise free and reconstructed) of the FIG. 102B, on a different scale.

[00590] DIAMOND NITROGEN VACANCY SENSOR WITH CIRCUITRY ON DIAMOND

[00591] Described below are DNV magnetic sensors with a sensor assembly that provide a number of advantages over magnetic sensor systems where the optical excitation sources, RF excitation source, and optical detectors are all formed on different substrates or as separate components mechanically supported. The sensor assembly described provides for a diamond NV sensor system in a single compact homogeneous device. Providing the optical excitation sources and the optical detectors on the same assembly substrate, such as on a same silicon wafer, reduces the overall system cost, size and weight. Providing the RF excitation source directly on the NV diamond material reduces the overall system size and weight. Providing the optical detectors directly on the NV diamond material reduces the amount of the red fluorescence emitted by the NV centers lost to the surroundings, which improves the system efficiency. Providing the optical excitation sources directly on the NV diamond material increases the amount of the optical excitation light by drastically reducing the amount of optical excitation light lost to the environment. Combining the optical excitation sources, RF excitation source, and optical detectors directly on the NV diamond material results in a significant size reduction that results in NV diamond sensors that are usable in small consumer and industrial products.

[00592] A sensor assembly 10300, which includes a base substrate 10310 and a diamond assembly 10320, or a material assembly generally, of aNV center magnetic sensor according to an embodiment, is illustrated in FIGs. 103 A, 103B, 104A, 104B, 104C and 105. FIGs. 103 A and 103B respectively illustrates a top perspective view, and a bottom perspective view of the sensor assembly 10300. FIGs. 104A and 104B respectively illustrate a top perspective view, and a bottom perspective view of the diamond assembly 10320. FIG. 104C illustrates a side view of an assembly substrate 10350 of the diamond assembly 10320. FIG. 105 illustrates a top view of the diamond assembly 10320.

[00593] The sensor assembly 10300 includes abase substrate 10310, and a diamond assembly 10320 arranged on the base substrate 10310. The sensor assembly 10300 further includes power/logic circuits 10330, which may be in the form of chips, mounted on the base substrate 10310, both on atop surface 10312 adjacent the diamond assembly 10320, and on bottom surface 10314 opposite to the top surface 10312. Attachment elements 10340, such as screws for example, extending in the base substrate 10310, allow for the attachment of the sensor assembly 10300 to further components. The base substrate 10310 may be, for example, a printed circuit board (PCB).

[00594] The diamond assembly 10320 has the assembly substrate 10350, and NV diamond material 10352, or another magneto-optical defect center material with magnetooptical defect centers, formed over the assembly substrate 10350. As best seen in FIGs 104A and 105, the diamond assembly 10320 includes a plurality of optical excitation sources 10354 and a plurality of optical detectors 10356 on, or embedded in, the assembly substrate 10350.

An RF excitation source 10358 is formed on the NV diamond material 10352, and connected to an RF connector 10360. The optical excitation sources 10354 and the RF excitation source 10358 are in general terms electromagnetic excitation sources.

[00595] As seen in FIGs. 103 A, 104A and 105, the optical excitation sources 10354 and the optical detectors 10356 may be arranged in an alternating fashion, such as the checkerboard arrangement shown. While FIGs. 103 A, 104A and 105 illustrate an arrangement with four optical excitation sources 10354 and five optical detectors 10356, other numbers of optical excitation sources 10354 and optical detectors 10356 are contemplated. The alternating arrangement of the optical excitation sources 10354 and the optical detectors 10356 reduces the amount of the red fluorescence emitted by the NV diamond material 10352 lost to the surroundings, which improves the system efficiency The optical excitation sources 10354 and the optical detectors 10356 need not be arranged in an alternating fashion.

[00596] As seen in FIGs. 104B and 104C, a bottom surface 10362 of the assembly substrate 10350, opposite to a top surface 10366 adjacent the NV diamond material 10352, has a plurality of connection pads 10364. Conductive through connections 10368 electrically connect the connection pads 10364 to the top surface 10366, and electrically connect to the optical excitation sources 10354 and the plurality of optical detectors 10356 to allow control of the optical excitation sources 10354 and to receive optical signals from the plurality of optical detectors 10356. The power/logic circuits 10330 are electrically connected to the connection pads 10364 via wirings 10334 on the base substrate 10310, to allow control of the optical excitation sources 10354 and to receive optical signals from the plurality of optical detectors 10356. In the case the power/logic circuits 10330 are mounted on the bottom surface 10314 of the base substrate 10310, the wirings 10334 may extend through the base substrate 10310 to those power/logic circuits 10330.

[00597] A power/logic connector 10332 is electrically connected to the power/logic circuits 10330. The power/logic connector 10332 includes a plurality of connectors 10333, which allow for connection of power/logic circuits 10330 to a power source and controller (not shown in FIGs. 103A-105) external to the sensor assembly 10300, such as the controller 680 illustrated in FIG. 6. The control functions may be split between the power logic circuits 10330 and the external controller. Similarly, the RF connector 10360 allows for connection of the RF excitation source 10358 to a power source and controller (not shown in FIGs. 103A-105) outside the sensor assembly 10300, such as the controller 680 illustrated in FIG. 6.

[00598] The assembly substrate 10350 may be a semiconductor material, such as silicon, upon which the plurality of optical excitation sources 10354 and a plurality of optical detectors 10356 are formed. The assembly substrate 10350 may be a silicon wafer, for example. The optical excitation sources 10354 may be laser diodes or light emitting diodes (LEDs), for example. The optical excitation sources 10354 emit light which excites fluorescence in the NV diamond material 10352, and may emit in the green, such at a wavelength of about 532 nm or 518nm, for example. Preferably, the excitation light is not in the red so as to not interfere with the red fluorescent light collected and detected. The optical detectors 10356 detect light, and in particular detect light in the red fluorescence band of the NV diamond material 10352. The optical excitation sources 10354 and the optical detectors 10356 may be formed on a single silicon wafer as the assembly substrate 10350 using fabrication techniques known for silicon fabrication, such as doping, ion implantation, and patterning techniques.

[00599] The power/logic circuits 10330 and the power/logic connecter 10332 are mounted on the base substrate 10310, which may be a PCB. The mounting may be performed by soldering, for example. Once the optical excitation sources 10354 and the optical detectors 10356 are formed on the assembly substrate 10350, the NV diamond material 10352 is attached with the assembly substrate 10350.

[00600] The RF excitation source 10358 may be formed on the NV diamond material 10352 in the form of a coil as seen in FIG. 104A, for example. The RF excitation source 10358 acts as a microwave RF antenna. The RF excitation source 10358 may be formed by forming a metal material on the NV diamond material 10352 followed by patterning the metal material. The metal material may be patterned by photolithography techniques, for example.

[00601] As shown in FIGs. 106A and 106B, the metal material may be formed on the NV diamond material 10352 first by forming a thin film seed layer 10370 on the NV diamond material 10352, followed by depositing a film metallization 10372 on the seed layer 10370.

The seed layer 10370 may be, for example, TiW, and the film metallization 10372 may be Cu, for example. Once the seed layer 10370 and the film metallization 10372 are formed, they are patterned, such as by photolithography techniques, for example, to form the RF excitation source 10358 into a coil shape. The RF connector 10360 is then formed at one end of the coil shaped RF excitation source 10358.

[00602] The sensor assembly described herein provides a number of advantages over magnetic sensor systems where the optical excitation sources, RF excitation source, and optical detectors are all formed on different substrates or as separate components mechanically supported. The sensor assembly described provides for a diamond NV sensor system in a single compact homogeneous device. Providing the optical excitation sources and the optical detectors on the same assembly substrate, such as on a same silicon wafer, reduces the overall system cost, size and weight. Providing the RF excitation source directly on the NV diamond material reduces the overall system size and weight. Providing the optical detectors directly on the NV diamond material reduces the amount of the red fluorescence emitted by the NV centers lost to the surroundings, which improves the system efficiency. Providing the optical excitation sources directly on the NV diamond material increases the amount of the optical excitation light by drastically reducing the amount of optical excitation light lost to the environment. Combining the optical excitation sources, RF excitation source, and optical detectors directly on the NV diamond material results in a significant size reduction that results in NV diamond sensors that are usable in small consumer and industrial products.

[00603] FIGs. 107A and 107B illustrate a diamond assembly according to another embodiment. In this embodiment the RF excitation source 10358, which may comprise a first RF excitation source 10358a and second RF excitation source 10358b, is larger in the plane of the NV diamond material 10352 than the NV diamond material 10352. The first RF excitation source 10358a and the second RF excitation source 10358b are on opposite sides of the NV diamond material 10352. The plane of the NV diamond material 10352 is horizontal and into the page in FIG. 107A, and is parallel to the page in FIG. 107B. While FIGs. 107A and 107B illustrate two RF excitation source 10358a and 10358b, only a single RF excitation source may be provided. The diamond assembly of FIGs. 107A and 107B further may include optical detectors 10356 and optical excitation sources 10354 in a similar fashion to earlier disclosed embodiments.

[00604] The shape of first RF excitation source 10358a and second RF excitation source 10358a may be spiral as shown in FIG. 107A (as well as in FIGs. 103A, 104A and 105). The spiral shape provides a maximum field with low driving power, thus providing good efficiency. Moreover, the spiral shape allows for the coil of the RF excitation source to be made larger, which allows for a more uniform field over a larger device.

[00605] The size of the first RF excitation source 10358a and second RF excitation source 10358a in the plane of the top surface 10380 of the NV diamond material 10352 is greater than a size of the top surface 10380 in the plane. The greater size allows for a more uniform field provided by the RF excitation sources 10358a and 10358b applied to the NV diamond material 10352. In this regard, the RF excitation sources 10358a and 10358b are on the NV diamond material 10352, but further extend to a support material 10700 laterally adjacent the NV diamond material 10352. The support material may be a material other than diamond, or may be diamond substantially without NV centers, for example. The size of the first RF excitation source 10358a and second RF excitation source 10358a in the plane of the top surface 10380 of the NV diamond material 10352 is also greater than a size of a detector region 10702 which includes the optical detectors 10356.

[00606] HIGHER MAGNETIC SENSITIVITY THROUGH FLUORESCENCE MANIPULATION BY PHONON SPECTRUM CONTROL

[00607] In some aspects of the present technology, methods and systems are disclosed for providing higher magnetic sensitivity magnetometers through fluorescence manipulation by phonon spectrum control. For diamond nitrogen-vacancy sensors, optical contrast between a resonant microwave frequency and an off resonant frequency fundamentally determines sensitivity. The total fluorescence of the system is a combination of the desired negatively charged NV centers (NV-) and the magnetically neutral uncharged NV centers (NV°).The subject technology can manipulate the phonon spectrum to alter the phonon sideband of fluorescence spectrum of both the NV° and NV' centers. During room temperature operation, the NV° fluorescence spectrum overlaps with the NV' spectrum. Thus, generating separation between these overlapping spectrums by altering the phonon mediated spectrum allows a filter to be used with the magnetometer device and/or with the data output from the magnetometer device to filter out the unwanted spectrum of NV° photon emissions while reducing the amount of NV' photon emissions filtered out.

[00608] In the context of DNV spectrometry, optical contrast is defined by ratio of NV' photon emissions to total fluorescence. The total fluorescence is a combination of NV° photon emissions, NV' photon emissions, and a ratio of photon emissions transmitted to scattered optical drive, such as transmitted into the diamond of the DNV and/or absorbed by other nitrogen vacancies. The optical drive is traditionally higher energy and narrowband making it easy to filter out. The majority of fluorescence from NV° centers and NV'centers that originates from a phonon sideband is a function of the energy versus momentum (E vs. k). That is, the fluorescence from the NV° centers and NV'centers that originates from the phonon sideband is a function of the applied optical drive and the momentum imparted by a phonon assisting the transition of the electron from the conduction band to the valence band. The width and shape of the spectral content of the photon emissions is thus a function of the combination of the phonon spectrum and the E vs. k variation.

[00609] At room temperature, the fluorescence of wavelengths of the NV° photon emissions and the NV' photon emissions overlap because the phonon spectrum is dominated by temperature. Controlling the phonon spectrum can alter the response fluorescence spectrum, which can allow the spectrum profile of wavelengths of the NV° photon emissions and the NV' photon emissions to be narrowed. By narrowing the spectrum profiles, the peaks of the NV° photon emissions at a particular wavelength and the NV' photon emissions at another particular wavelength display a more defined difference in fluorescence intensity peaks based on the greater separation of the NV° and NV' spectra. The more defined fluorescence intensity peaks can permit a filter, such as a long pass filter, to be used to filter out the unwanted NV° photon emissions, thereby increasing the optical contrast for the remaining NV' photon emissions.

[00610] The NV° and NV' spectra can be manipulated through acoustic driving and diamond shape optimization that affects the phonon spectrum experienced by the NV° centers and NV' centers. For instance, acoustic driving can increase and/or control the phonon spectrum by generating phonons within the lattice structure of the diamond at a specific frequency or at a set of specific frequencies. The generation of phonons at a specific frequency can narrow the phonons experienced by the NV centers within the diamond such that the effects of other phonons, e.g., lattice vibrations, such as those introduced based upon the temperature of the material, may be reduced. The narrowing of phonons experienced by the NV centers can result in sharper wavelength intensity peaks for the NV° photon emissions and the NV' photon emissions. Thus, by acoustically driving the diamond at a particular frequency, the bandwidth of the NV° and NV' spectra can be narrowed to permit optical filtering. In some implementations, the shape of the diamond can be modified to enhance the phonon spectrum by modifying the resonance of the diamond. The resonance of the diamond can also narrow the phonons experienced by the NV° and NV' centers. In some further implementations, the optical drive applied to the diamond of the DNV sensor may be matched with a NV° zero phonon line to decrease the phonon sideband.

[00611] FIG. 108 is a graphical diagram 10800 depicting an example of a DNV optical fluorescence spectrum from NV° centers and NV' centers. For a DNV based optically detected magnetic resonance (ODMR) sensor, the meaningful signal is a change in fluorescence of the NV' states, indicating a resonant energy level. The inactive NV° fluorescence spectrum 10820, however, overlaps the desired signal of the NV' fluorescence spectrum 10810. Thus, for a large portion of the NV' fluorescence spectrum 10810, the NV° fluorescence spectrum 10820 causes a large background signal that is subject to noise and that ultimately raises the noise floor and reduces magnetic field detection sensitivity. The majority of the spectral content of the NV fluorescence spectrum is the result of the phonon mediated transitions. In some materials, such as indirect bandgap materials, exciton recombination requires absorption of a phonon and release of a photon. The released photon is the fluorescence of the NV' fluorescence spectrum 10810 and/or NV° fluorescence spectrum 10820 shown in FIG. 108. In room temperature diamonds, there is a Boltzmann distribution of phonon energies dictated by the temperature and variations in vibrations experienced in the lattice structure of the diamond, resulting in a broad phonon spectrum that can be experienced by the NV° and NV' centers of the diamond. Thus, the broad phonon spectrum results in the broad bandwidth of the NV' fluorescence spectrum 10810 and NV° fluorescence spectrum 10820 as shown in FIG. 108. The NV' fluorescence spectrum 10810 and NV° fluorescence spectrum 10820 overlap, thus resulting in an increase in the background of the signal and low optical contrast.

[00612] FIG. 109 depicts an energy vs. momentum diagram 10900 for the indirect band gap of a diamond of a DNV sensor showing a valence band 10910 and a conduction band 10920. When an optical drive 10930 is applied to and absorbed by an electron in the valence band 10910, the excited electron is elevated to the conduction band 10920. When the electron returns to the ground state from the conduction band 10920 through recombination, a photon is emitted. When electrons in a diamond of a DNV sensor recombine from various points of the conduction band 10920, such as due to the phonon sideband, a fluorescence spectrum of photons 10950 are emitted as shown in FIG. 108. In some implementations, matching the optical drive frequency 10930 with a zero phonon line (ZPL) 10940 can decrease the phonon sideband, thereby increasing the optical contrast. However, at low temperatures, such as near 0 Kelvin, the vibrational energy due to temperature is minimal, which results in a minimal phonon sideband. The energy of the resulting photons is hoy where h is the Plank constant and ω is the angular frequency, which is equal to 2π/j where/is the frequency. Thus, when an optical drive 10930 is applied along a zero phonon line (ZPL) 10940, the fluorescence spectrum would include a single peak at the ZPL frequency when a fluorescence photon 10950 is emitted. If vibrational energy is introduced into the diamond at such low temperatures, such as through an acoustic driver, then the added vibrational energy results in phonon energy, hPh0non, that can be imparted to the electrons in the momentum direction of the diagram 10900 for phonon assisted transitioning. The resulting fluorescence photons 10950 emitted from the phonon driven electrons results in a second peak for the driven vibrational frequency. The driven vibrational frequency can be adjusted to narrow the phonon spectrum at room temperature, thereby narrowing the fluorescence spectrum for the photons 10950 that are emitted from the diamond at room temperature. In some implementations, the shape of the diamond can be modified to manipulate the phonon spectrum by modifying the resonance of the diamond, either separately or in addition to the driven vibrational frequency.

[00613] FIG. 110 illustrates is a graphical diagram 11000 depicting NV° and NV' photon intensity spectra relative to wavelength with fluorescence manipulation. As shown in FIG. 110, the desired signal of the NV' fluorescence spectrum 11010 and the inactive NV° fluorescence spectrum 11020 include narrower bandwidths for the peaks at particular frequencies due to controlling the phonon spectrum that alters the response fluorescence spectrum. The phonon spectrum manipulation can be controlled through acoustic driving and/or diamond size and/or shape optimization. The narrow bandwidth peaks allows for greater separation between the NV° and NV' spectra, which enables the use of filtering to increase optical contrast. For instance, a filter, such as a long pass filter, can be used to filter out the unwanted NV° photon emissions while filtering a minimal amount of NV' photon emissions, thereby increasing the optical contrast. The subject technology provides a device that can control the phonon content within the diamond resulting in a controlled spectral content. This allows for better background suppression and overall greater optical contrast. The optical contrast can be directly related to the overall system sensitivity. For instance, with narrower bandwidth peaks for the NV' fluorescence spectrum 11010, smaller changes in magnitude of an external magnetic field can be detected. In some instances, controlling the phonon spectrum within the diamond may allow achieving an optical contrast that approaches the theoretical limit or approximately 25%.

[00614] FIG. Ill depicts a method 11100 for fluorescence manipulation of a diamond having nitrogen vacancies through phonon spectrum manipulation using an acoustic driver. The method 11100 includes providing a diamond having nitrogen vacancies and an acoustic driver (block 11102). The diamond having nitrogen vacancies can be part of a DNV sensor that includes a photo detector configured to detect photon emissions from the diamond responsive to laser excitation of the diamond. The acoustic driver may be a piezoelectric acoustic driver or any other acoustic driver for inducing vibrations to the diamond. In some implementations, the acoustic driver may be coupled to the diamond to directly impart vibrational energy to the diamond or may be spaced apart from the diamond to indirectly impart vibrational energy to the diamond. In some implementations, the acoustic driver may be positioned relative to the diamond such that the acoustic driver drives the diamond parallel to the nitrogen vacancies of a lattice of the diamond.

[00615] The method 11100 may include modifying a shape and/or size of the diamond to manipulate a phonon spectrum based on resonance of the diamond (block 11104). The shape of the diamond may be modified to alter the internal resonance of the diamond such that the phonons resulting from the vibrational energy imparted based on the temperature can be narrowed for the phonon spectrum. In some instances, the size of the diamond may also be modified to alter the resonance to manipulate the phonon spectrum.

[00616] The method 11100 further includes acoustically driving the diamond with the acoustic driver to manipulate the phonon spectrum (block 11106). Acoustically driving the diamond may include activating the acoustic driver at a particular frequency to narrow the phonon spectrum. In some implementations, the acoustic driver may be a piezoelectric acoustic driver. In some implementations, the acoustic driver may be positioned relative to the diamond such that the acoustic driver drives the diamond parallel to the nitrogen vacancies of a lattice of the diamond.

[00617] The method may include applying a long pass filter to filter NV° photon emissions from NV' photon emissions (block 11108). The filter, such as a long pass filter, can be used to filter out the unwanted NV° photon emissions while filtering a minimal amount of NV' photon emissions, thereby increasing the optical contrast. In some implementations, the long pass filter may be incorporated into the photo detector of the DNV sensor and/or may be applied to data output from the photo detector.

[00618] FIG. 112 depicts a method 11200 for determining an acoustic driving frequency for phonon spectrum manipulation for a DNV sensor. The method 11200 can include subjecting a diamond of a DNV sensor to near 0 Kelvin (block 11202). The diamond of the DNV sensor includes nitrogen vacancies and the DNV sensor may include a photo detector configured to detect photon emissions from the diamond responsive to laser excitation of the diamond. Subjecting the diamond to near 0 Kelvin may include cryogenically cooling the diamond to a near 0 Kelvin temperature.

[00619] The method 11200 includes acoustically driving the diamond having nitrogen vacancies of the DNV sensor at a first frequency using an acoustic driver (block 11204). Acoustically driving the diamond may include activating the acoustic driver at a particular frequency to narrow the phonon spectrum. In some implementations, the acoustic driver may be a piezoelectric acoustic driver. In some implementations, the acoustic driver may be positioned relative to the diamond such that the acoustic driver drives the diamond parallel to the nitrogen vacancies of a lattice of the diamond. The first frequency can be a randomly selected frequency, a frequency within a range of frequencies, and/or a frequency based on a frequency response output.

[00620] The method 11200 includes detecting a first set of NV° photon emissions and a first set of NV' photon emissions from the DNV sensor (block 11206). The detection of the first set of NV° photon emissions and the first set of NV' photon emissions from the DNV sensor may include receiving and processing data from a photo detector of the DNV sensor. In some implementations, the first set of NV° photon emissions and the first set of NV' photon emissions from the DNV sensor may form spectra such as those shown in FIGS. 108 or 110.

[00621] The method 11200 includes acoustically driving the diamond having nitrogen vacancies of the DNV sensor at a second frequency using an acoustic driver (block 11208). The second frequency can be a randomly selected frequency, a frequency within a range of frequencies, and/or a frequency based on a frequency response output.

[00622] The method 11200 includes detecting a second set of NV° photon emissions and a second set of NV' photon emissions from the DNV sensor (block 11210). The detection of the second set of NV° photon emissions and the second set of NV' photon emissions from the DNV sensor may include receiving and processing data from a photo detector of the DNV sensor. In some implementations, the second set of NV° photon emissions and the second set of NV' photon emissions from the DNV sensor may form spectra such as those shown in FIGS. 108 or 110.

[00623] The method 11200 includes selecting the second frequency for acoustically driving the diamond with the acoustic driver to manipulate a phonon spectrum based on a wavelength difference between a peak of the second set of NV° photon emissions and the second set of NV' photon emissions from the DNV sensor (block 11212). The selection of the second frequency may be based on the second frequency producing a fluorescence spectrum similar to FIG. 110 rather than FIG. 108. In some implementations, the method 11200 may include applying a long pass filter to filter NV° photon emissions from NV' photon emissions detected by the photo detector. In some implementations, the method 11200 can include modifying a shape of the diamond to manipulate the phonon spectrum based on resonance of the diamond.

[00624] MAGNETOMETER WITH LIGHT PIPE

[00625] In many instances, a light source is used to provide light to the diamond. The more light that is transmitted through the diamond, the more light can be detected and analyzed to determine the amount of red light emitted from the diamond. The amount of red light can be used to determine the strength of the magnetic field applied to the diamond. In some instances, photo detectors used to detect the amount of red light (or any suitable wavelength of light) are sensitive to electromagnetic interference (EMI). However, in some cases electromagnetic signals can be emitted from electrical components near the diamond. In such cases, EMI from the diamond assembly can affect the photo detectors.

[00626] In some cases, EMI glass can be used to block and/or absorb EMI signals from the diamond assembly (or associated electronics or signals). Thus, if EMI glass is placed between the diamond and the photo detector, the amount of EMI affecting the photo detector can be reduced. To increase the sensitivity of the magnetometer, the amount of light emitted from the diamond that is sensed by the photo detector can be increased. Thus, in some instances, sensitivity of the magnetometer is reduced by inefficient transmission of light between the diamond and the photo detector. In many instances, EMI glass is an inefficient transmitter of light. For example, metal embedded in the EMI glass can absorb, block, or reflect light traveling through the EMI glass.

[00627] In some embodiments, an EMI shield can be used to block EMI from the diamond assembly. In such embodiments, the EMI shield may include a hole that allows light to pass to or from the diamond. Depending upon the size of the hole in the EMI shield, some EMI may pass through the hole. Thus, the smaller the hole, the more EMI is prevented from passing through.

[00628] In some instances, a light pipe may be used to transmit light through the hole in the EMI shield. For example, light from a light source can pass through a diamond and through a hole in an EMI shield. The light can be collected by a light pipe and travel through the light pipe to a photo detector. In general, light pipes are efficient at transmitting light. Thus, a relatively high percentage of light that is emitted from the diamond can be transferred to the photo detector. Any suitable light pipe (e.g., a homogenizing rod) can be used.

[00629] Fig. 113 A is a block diagram of a magnetometer with a light pipe in accordance with an illustrative embodiment. An illustrative magnetometer 11300 includes a light source 11305, a diamond 11315, a light pipe 11325, a photo detector 11335, and a shield 11345. In alternative embodiments, additional, fewer, and/or different elements may be used.

[00630] As explained above, the magnitude of the magnetic field applied to the diamond 11315 by, for example, a magnet 11340 can be determined by measuring the amount of red light in the light emitted from the diamond 11315. The light source 11305 emits source light 11310 to the diamond 11315. In some embodiments, one or more components can be used to focus the source light 11310 to the diamond 11315. The light passes through the diamond 11315, and the modulated light 11320 passes through the hole in the shield 11345. To pass through the hole in the shield 11345, the modulated light 11320 enters and passes through the light pipe 11325. The transmitted light 11330, which passed through the hole in the shield 11345, exits the light pipe 11325 and is detected by the photo detector 11335.

[00631] Any suitable photo detector 11335 can be used. In an illustrative embodiment, the photo detector 11335 includes one or more photo diodes. In some embodiments, the photo detector 11335 can be an image sensor. The image sensor can be configured to detect light and/or electromagnetic waves. The image sensor can be a semiconductor charge-coupled device (CCD) or an active pixel sensor in complementary metal-oxide-semiconductor (CMOS) or N-type metal-oxide-semiconductor (NMOS) technologies. Any other suitable image sensor can be used.

[00632] In some instances, the diamond 11315 is surrounded by one or more components that emit EMI. For example, a Helmholtz coil can surround the diamond. In some instances, a twodimensional or a three-dimensional Helmholtz coil can be used. For example, the Helmholtz coil can be used to cancel out the earth's magnetic field by applying a magnetic field with an equal magnitude but opposite direction of the earth's magnetic field. In alternative embodiments, the Helmholtz coil can be used to cancel any suitable magnetic field and/or apply any suitable magnetic field to the diamond. In another example, a microwave generator and/or modulator can be located near the diamond to use microwaves to excite the NV centers of the diamond. The microwave generator and/or modulator can emit EMI that can interfere with the photo detectors.

[00633] The shield 11345 can shield the photo detector 11335 from the EMI. For example, the shield 11345 can be a material that attenuates electromagnetic signals. In some embodiments, the shield 11345 can be solid metal such as a metal foil. In alternative embodiments, materials such as glass, plastic, or paper can be coated or infused with a metal. Protecting the photo detector 11335 from EMI allows the magnetometer to be more sensitive because the reduction in EMI reduces the amount of noise in the signal received from the photo detector 11335. In some instances, protecting the photo detector 11335 from EMI protects the fidelity of the magnetometer because the signal received from the photo detector 11335 is more accurate. That is, protecting the photo detector 11335 from EMI helps to ensure that a reliable and accurate signal is received from the photo detector 11335 because there is less noise in the signal. For example, the noise may include a direct current (DC) offset.

[00634] The light pipe 11325 can be made of any suitable material. For example, the light pipe 11325 can be made of quartz, silica, glass, etc. In an illustrative embodiment, the light pipe 11325 is made of optical glass such as BK7 or BK9 optical glass. In alternative embodiments, any suitable material can be used.

[00635] In some embodiments, one or more of the faces of the light pipe 11325 can include a filter. For example, the face of the light pipe 11325 can filter out non-green light and allow green light to pass through the light pipe 11325, for example, to the diamond 11315. In another example, light from diamond can pass through a face of the light pipe 11325 that filters out nonred light and permits red light to pass through the light pipe 11325 to the photo detector 11335. In alternative embodiments, any suitable filtering mechanism can be used.

[00636] Figs. 113B and 113C are isometric views of a light pipe and a shield in accordance with illustrative embodiments. In alternative embodiments, additional, fewer, and/or different elements may be used. As shown in Fig. 113B, the light pipe 11325 is surrounded axially by the shield 11345. In an illustrative embodiment, the light pipe 11325 and the shield 11345 are coaxial. The cross-sectional shape of the light pipe 11325 can be any suitable shape. In the embodiment illustrated in Fig. 113B, the cross-sectional shape of the light pipe 11325 is circular. In the embodiment illustrated in Fig. 113C, the cross-sectional shape of the light pipe 11325 is octagonal. In alternative embodiments, the cross-sectional shape of the light pipe 11325 can be triangular, square, rectangular, or any other suitable shape. Similarly, in the cross-sectional shape of the shield 11345 can be any suitable shape. In an illustrative embodiment, the outer shape of the shield 11345 is suited to fit against the wall of a housing that houses the diamond 11315, the photo detector 11335, the lightpipe 11325, etc.

[00637] In the embodiments illustrated in Figs. 113B and 113C, the length of the light pipe 11325 is the same as the length of the shield 11345. In alternative embodiments, the light pipe 11325 can be longer than the shield 11345. For example, the light pipe 11325 may extend beyond the end surface of the shield 11345 at one or both ends. In an illustrative embodiment, the shield 11345 is one inch long. In alternative embodiments, the shield 11345 can be shorter or longer than one inch long. For example, in embodiments in which greater attenuation is beneficial, such as with a more sensitive photo detector 11335, the shield 11345 can be longer.

In an illustrative embodiment, the light pipe 11325 can be two inches long. In alternative embodiments, the light pipe 11325 can be shorter or longer than two inches long. For example, the light pipe 11325 can be a length suitable to fit within a housing or arrangement of elements.

[00638] In some embodiments, the light pipe 11325 can be tapered along the length of the light pipe 11325. For example, the diameter of the light pipe 11325 at one end can be large than the diameter of the light pipe 11325 at the opposite end. Any suitable ratio of diameters can be used. In an illustrative embodiment, a light pipe 11325 can be used to transmit light from the light source 11305, which can be a light emitting diode, to the diamond 11315. Using a tapered light pipe 11325 can help to focus the light exiting the light pipe 11325 to enter the diamond 11315 at a more perpendicular angle than if a non-tapered light pipe 11325 were to be used. In such an example, the narrow end can be adjacent to the light source 11305 and the wide end can be adjacent to the diamond 11315.

[00639] The size of the aperture in the middle of the shield 11345 can be sized to block one or more particular frequencies of EMI. For example, the diameter of the light pipe 11325 can be between five and six millimeters. In alternative embodiments, the diameter of the light pipe 11325 can be less than five millimeters or greater than six millimeters. In an illustrative embodiment, the light pipe 11325 is sized to have a cross-sectional area that is the same size or slightly larger than a cross-sectional diameter of the diamond 11315. In such embodiments, the light pipe 11325 is sized to capture as much of the light emitted from the diamond 11315 as possible while minimizing the inner diameter of the shield 11345 (and, therefore, maximizing the shielding effect of the shield 11345).

[00640] In an illustrative embodiment, light from an LED that enters the light pipe 11325 in an uneven pattern can exit the light pipe 11325 in a more uniform pattern. That is, the light pipe 11325 can evenly distribute the light over the surface area of the diamond 11315 or the photo detector 11335. The light pipe 11325 can prevent the light from diverging. Thus, in some embodiments, the light pipe 11325 can be used in place of a lens.

[00641] The outer diameter of the shield 11345 can be any suitable size. For example, the outer diameter of the shield 11345 can be sized to block or attenuate electromagnetic signals from the diamond apparatus thereby protecting the photo detector.

[00642] As illustrated in Figs. 113A-113C, the light pipe 11325 passes through the shield 11345. That is, the shield 11345 surrounds the light pipe 11345 along at least a length of the light pipe 11325. In some embodiments, the shield 11345 surrounds the length of the light pipe 11325.

[00643] Fig. 114 is a block diagram of a magnetometer with two light pipes in accordance with an illustrative embodiment. An illustrative magnetometer 11400 includes two light pipes 11325, two shields 11345, a diamond 11315, a photo detector 11335, and a photo detector 11350. In alternative embodiments, additional, fewer, and/or different elements may be used.

[00644] The magnetometer 11400 includes a light source 11305 that sends source light 11310 into a light pipe 11325. Some of the light transmitted from the light source 11305 can be sensed by the photo detector 11350. In some embodiments, the light sensed by the photo detector 11350 is transmitted through the light pipe 11325. In alternative embodiments, the light sensed by the photo detector 11350 does not travel through the light pipe 11325. As discussed above with regard to the magnetometer 11300, the diamond 11315 may be associated with electrical components that emit EMI that may interfere with the performance of the photo detector 11350. In such instances, one of the shield 11345 may be placed between the diamond 11315 and the photo detector 11350. Light from the light source 11305 may travel through the light pipe 11325, through the hole in the shield 11345, and into the diamond 11315.

[00645] As discussed with regard to the magnetometer 11300 of Fig. 113, a shield 11345 may be used to protect the photo detector 11335 from EMI emitted from circuitry associated with the diamond 11315. Thus, the magnetometer 11400 includes a shield 11345 on either side of the diamond 11315 and the electrical components associated with the diamond 11315.

[00646] Fig. 115 is a block diagram of a magnetometer with two light pipes in accordance with an illustrative embodiment. The magnetometer 11500 includes a light source 11305, a diamond 11315, two light pipes 11325 with associated shields 11345, and two photo detectors 11335. In alternative embodiments, additional, fewer, and/or different elements may be used. In the embodiment illustrated in Fig. 115, the source light 11310 from the light source 11305 passes through the diamond 11315. The light that enters the diamond 11315 can be split and can exit the diamond 11315 in two streams of modulated light 11320. In some embodiments, the two streams of modulated light 11320 are in opposite directions. In alternative embodiments, the two streams of modulated light 11320 are in any suitable orientation to one another. In some embodiments, the two streams of modulated light 11320 exit the diamond 11315 in directions orthogonal to the direction in which the source light 11310 enters the diamond 11315.

[00647] Fig. 115 illustrates a magnetometer with two light streams exiting the diamond 11315. In alternative embodiments, the magnetometer can be used with three or more light streams that exit the diamond 11315. For example, if the diamond 11315 is a cube, light can enter the diamond 11315 on one of the six sides. In such an example, up to five light streams can exit the diamond 11315 via the five other sides. Each of the five light streams can be transmitted to one of five photo detectors 11335. Using two or more light streams that exit the diamond 11315, which are sensed by associated photo detectors 11335, can provide increased sensitivity. Each of the light streams contains the same information. That is, the light streams contain the same amount of red light. Each light stream provides one of the multiple photo detectors a sample of the light. Thus, in embodiments in which multiple light streams from the diamond are used, multiple samples of the same light are gathered. Having multiple samples provides redundancies and allows the system to verify measurements. In some embodiments, the multiple measurements can be averaged or otherwise combined. The combined value can be used to determine the magnetic field applied to the diamond.

[00648] Fig. 116 is a flow diagram of a method for measuring a magnetic field in accordance with an illustrative embodiment. In alternative embodiments, additional, fewer, and/or different operations may be performed. Also, the use of a flow chart and arrows is not meant to be limiting with respect to the order or flow of operations. For example, in some embodiments, one or more of the operations can be performed simultaneously.

[00649] In an operation 11605, light is generated by a light source. Any suitable light source can be used. For example, lasers or light emitting diodes can be used. In some embodiments, sunlight or environmental light can be used as the light source. In an illustrative embodiment, the light generated by the light source is green light or blue light. In some embodiments, a filter can be used to filter out undesirable light frequencies (e.g., red light).

[00650] In an operation 11610, light from the light source is sensed. In an illustrative embodiment, the light can be sensed using a photo detector. In some embodiments, the photo detector is sensitive to electromagnetic interference. In some embodiments, the operation 11610 is not performed. For example, in some embodiments, light from the diamond is sensed and the sensed light signal is compared to a pre-determined reference value.

[00651] In an operation 11615, light from the light source is transmitted through a first light pipe. In embodiments in which light from the light source is sensed using a photo detector located between the light source and the diamond, the first light pipe can be surrounded by a material that attenuates EMI. In such embodiments, EMI from electrical components near the diamond can be attenuated via the material such that the photo detector is not affected by or is less affected by the EMI. In some embodiments, such as those in which the operation 11610 is not performed, the operation 11615 may not be performed.

[00652] In an operation 11620, light from the light source is transmitted through the diamond. In embodiments in which the operation 11615 is performed, light from the first light pipe is transmitted through the diamond. As mentioned above, the diamond can include NV centers that are affected by magnetic fields. The amount of red light emitted from the diamond (e.g., via the NV centers) can change based on the applied magnetic field.

[00653] In an operation 11625, light emitted from the diamond is transmitted through a second light pipe. In an operation 11630, light from the second light pipe is sensed. In an illustrative embodiment, the light is sensed via a light detector that is sensitive to EMI. In such embodiments, the light pipe can be surrounded by material that attenuates EMI from electrical components near the diamond, such as a Helmholtz coil or a microwave generator/modulator.

[00654] In an operation 11635, a magnetic field point is determined. In an illustrative embodiment, the magnetic field point is a vector with a magnitude and a direction. In alternative embodiments, the operation 11635 includes determining a magnitude or a direction. In embodiments in which operation 11610 is performed, the operation 11635 can include comparing the amount of green light (or any other suitable wavelength) emitted from the light source with the amount of detected red light (or any other suitable wavelength) that was transmitted through the second light pipe. In alternative embodiments, the amount of detected red light that was transmitted through the second light pipe is compared to a baseline amount. In alternative embodiments, any suitable method of determining the magnetic field point can be used.

[00655] In many instances, a light source is used to provide light to the diamond. The more light that is transmitted through the diamond, the more light can be detected and analyzed to determine the amount of red light emitted from the diamond. The amount of red light can be used to determine the strength of the magnetic field applied to the diamond. In some instances, photo detectors used to detect the amount of red light (or any suitable wavelength of light) are sensitive to electromagnetic interference (EMI). However, in some cases electromagnetic signals can be emitted from electrical components near the diamond. In such cases, EMI from the diamond assembly can affect the photo detectors.

[00656] In some cases, EMI glass can be used to block and/or absorb EMI signals from the diamond assembly (or associated electronics or signals). Thus, if EMI glass is placed between the diamond and the photo detector, the amount of EMI affecting the photo detector can be reduced. To increase the sensitivity of the magnetometer, the amount of light emitted from the diamond that is sensed by the photo detector can be increased. Thus, in some instances, sensitivity of the magnetometer is reduced by inefficient transmission of light between the diamond and the photo detector. In many instances, EMI glass is an inefficient transmitter of light. For example, metal embedded in the EMI glass can absorb, block, or reflect light traveling through the EMI glass.

[00657] In some embodiments, an EMI shield can be used to block EMI from the diamond assembly. In such embodiments, the EMI shield may include a hole that allows light to pass to or from the diamond. Depending upon the size of the hole in the EMI shield, some EMI may pass through the hole. Thus, the smaller the hole, the more EMI is prevented from passing through.

[00658] In some instances, a light pipe may be used to transmit light through the hole in the EMI shield. For example, light from a light source can pass through a diamond and through a hole in an EMI shield. The light can be collected by a light pipe and travel through the light pipe to a photo detector. In general, light pipes are efficient at transmitting light. Thus, a relatively high percentage of light that is emitted from the diamond can be transferred to the photo detector. Any suitable light pipe (e.g., a homogenizing rod) can be used.

[00659] Fig. 113 A is a block diagram of a magnetometer with a light pipe in accordance with an illustrative embodiment. An illustrative magnetometer 11300 includes a light source 11305, a diamond 11315, a light pipe 11325, a photo detector 11335, and a shield 11345. In alternative embodiments, additional, fewer, and/or different elements may be used.

[00660] As explained above, the magnitude of the magnetic field applied to the diamond 11315 by, for example, a magnet 11340 can be determined by measuring the amount of red light in the light emitted from the diamond 11315. The light source 11305 emits source light 11310 to the diamond 11315. In some embodiments, one or more components can be used to focus the source light 11310 to the diamond 11315. The light passes through the diamond 11315, and the modulated light 11320 passes through the hole in the shield 11345. To pass through the hole in the shield 11345, the modulated light 11320 enters and passes through the light pipe 11325. The transmitted light 11330, which passed through the hole in the shield 11345, exits the light pipe 11325 and is detected by the photo detector 11335.

[00661] Any suitable photo detector 11335 can be used. In an illustrative embodiment, the photo detector 11335 includes one or more photo diodes. In some embodiments, the photo detector 11335 can be an image sensor. The image sensor can be configured to detect light and/or electromagnetic waves. The image sensor can be a semiconductor charge-coupled device (CCD) or an active pixel sensor in complementary metal-oxide-semiconductor (CMOS) or N-type metal-oxide-semiconductor (NMOS) technologies. Any other suitable image sensor can be used.

[00662] In some instances, the diamond 11315 is surrounded by one or more components that emit EMI. For example, a Helmholtz coil can surround the diamond. In some instances, a twodimensional or a three-dimensional Helmholtz coil can be used. For example, the Helmholtz coil can be used to cancel out the earth’s magnetic field by applying a magnetic field with an equal magnitude but opposite direction of the earth’s magnetic field. In alternative embodiments, the Helmholtz coil can be used to cancel any suitable magnetic field and/or apply any suitable magnetic field to the diamond. In another example, a microwave generator and/or modulator can be located near the diamond to use microwaves to excite the NV centers of the diamond. The microwave generator and/or modulator can emit EMI that can interfere with the photo detectors.

[00663] The shield 11345 can shield the photo detector 11335 from the EMI. For example, the shield 11345 can be a material that attenuates electromagnetic signals. In some embodiments, the shield 11345 can be solid metal such as a metal foil. In alternative embodiments, materials such as glass, plastic, or paper can be coated or infused with a metal. Protecting the photo detector 11335 from EMI allows the magnetometer to be more sensitive because the reduction in EMI reduces the amount of noise in the signal received from the photo detector 11335. In some instances, protecting the photo detector 11335 from EMI protects the fidelity of the magnetometer because the signal received from the photo detector 11335 is more accurate. That is, protecting the photo detector 11335 from EMI helps to ensure that a reliable and accurate signal is received from the photo detector 11335 because there is less noise in the signal. For example, the noise may include a direct current (DC) offset.

[00664] The light pipe 11325 can be made of any suitable material. For example, the light pipe 11325 can be made of quartz, silica, glass, etc. In an illustrative embodiment, the light pipe 11325 is made of optical glass such as BK7 or BK9 optical glass. In alternative embodiments, any suitable material can be used.

[00665] In some embodiments, one or more of the faces of the light pipe 11325 can include a filter. For example, the face of the light pipe 11325 can filter out non-green light and allow green light to pass through the light pipe 11325, for example, to the diamond 11315. In another example, light from diamond can pass through a face of the light pipe 11325 that filters out nonred light and permits red light to pass through the light pipe 11325 to the photo detector 11335.

In alternative embodiments, any suitable filtering mechanism can be used.

[00666] Figs. 113B and 113C are isometric views of a light pipe and a shield in accordance with illustrative embodiments. In alternative embodiments, additional, fewer, and/or different elements may be used. As shown in Fig. 113B, the light pipe 11325 is surrounded axially by the shield 11345. In an illustrative embodiment, the light pipe 11325 and the shield 11345 are coaxial. The cross-sectional shape of the light pipe 11325 can be any suitable shape. In the embodiment illustrated in Fig. 113B, the cross-sectional shape of the light pipe 11325 is circular. In the embodiment illustrated in Fig. 113C, the cross-sectional shape of the light pipe 11325 is octagonal. In alternative embodiments, the cross-sectional shape of the light pipe 11325 can be triangular, square, rectangular, or any other suitable shape. Similarly, in the cross-sectional shape of the shield 11345 can be any suitable shape. In an illustrative embodiment, the outer shape of the shield 11345 is suited to fit against the wall of a housing that houses the diamond 11315, the photo detector 11335, the lightpipe 11325, etc.

[00667] In the embodiments illustrated in Figs. 113B and 113C, the length of the light pipe 11325 is the same as the length of the shield 11345. In alternative embodiments, the light pipe 11325 can be longer than the shield 11345. For example, the light pipe 11325 may extend beyond the end surface of the shield 11345 at one or both ends. In an illustrative embodiment, the shield 11345 is one inch long. In alternative embodiments, the shield 11345 can be shorter or longer than one inch long. For example, in embodiments in which greater attenuation is beneficial, such as with a more sensitive photo detector 11335, the shield 11345 can be longer.

In an illustrative embodiment, the light pipe 11325 can be two inches long. In alternative embodiments, the light pipe 11325 can be shorter or longer than two inches long. For example, the light pipe 11325 can be a length suitable to fit within a housing or arrangement of elements.

[00668] In some embodiments, the light pipe 11325 can be tapered along the length of the light pipe 11325. For example, the diameter of the light pipe 11325 at one end can be large than the diameter of the light pipe 11325 at the opposite end. Any suitable ratio of diameters can be used. In an illustrative embodiment, a light pipe 11325 can be used to transmit light from the light source 11305, which can be a light emitting diode, to the diamond 11315. Using a tapered light pipe 11325 can help to focus the light exiting the light pipe 11325 to enter the diamond 11315 at a more perpendicular angle than if a non-tapered light pipe 11325 were to be used. In such an example, the narrow end can be adjacent to the light source 11305 and the wide end can be adjacent to the diamond 11315.

[00669] The size of the aperture in the middle of the shield 11345 can be sized to block one or more particular frequencies of EMI. For example, the diameter of the light pipe 11325 can be between five and six millimeters. In alternative embodiments, the diameter of the light pipe 11325 can be less than five millimeters or greater than six millimeters. In an illustrative embodiment, the light pipe 11325 is sized to have a cross-sectional area that is the same size or slightly larger than a cross-sectional diameter of the diamond 11315. In such embodiments, the light pipe 11325 is sized to capture as much of the light emitted from the diamond 11315 as possible while minimizing the inner diameter of the shield 11345 (and, therefore, maximizing the shielding effect of the shield 11345).

[00670] In an illustrative embodiment, light from an LED that enters the light pipe 11325 in an uneven pattern can exit the light pipe 11325 in a more uniform pattern. That is, the light pipe 11325 can evenly distribute the light over the surface area of the diamond 11315 or the photo detector 11335. The light pipe 11325 can prevent the light from diverging. Thus, in some embodiments, the light pipe 11325 can be used in place of a lens.

[00671] The outer diameter of the shield 11345 can be any suitable size. For example, the outer diameter of the shield 11345 can be sized to block or attenuate electromagnetic signals from the diamond apparatus thereby protecting the photo detector.

[00672] As illustrated in Figs. 113A-113C, the light pipe 11325 passes through the shield 11345. That is, the shield 11345 surrounds the light pipe 11345 along at least a length of the light pipe 11325. In some embodiments, the shield 11345 surrounds the length of the light pipe 11325.

[00673] Fig. 114 is a block diagram of a magnetometer with two light pipes in accordance with an illustrative embodiment. An illustrative magnetometer 11400 includes two light pipes 11325, two shields 11345, a diamond 11315, a photo detector 11335, and a photo detector 11350. In alternative embodiments, additional, fewer, and/or different elements may be used.

[00674] The magnetometer 11400 includes a light source 11305 that sends source light 11310 into a light pipe 11325. Some of the light transmitted from the light source 11305 can be sensed by the photo detector 11350. In some embodiments, the light sensed by the photo detector 11350 is transmitted through the light pipe 11325. In alternative embodiments, the light sensed by the photo detector 11350 does not travel through the light pipe 11325. As discussed above with regard to the magnetometer 11300, the diamond 11315 may be associated with electrical components that emit EMI that may interfere with the performance of the photo detector 11350. In such instances, one of the shield 11345 may be placed between the diamond 11315 and the photo detector 11350. Light from the light source 11305 may travel through the light pipe 11325, through the hole in the shield 11345, and into the diamond 11315.

[00675] As discussed with regard to the magnetometer 11300 of Fig. 113, a shield 11345 may be used to protect the photo detector 11335 from EMI emitted from circuitry associated with the diamond 11315. Thus, the magnetometer 11400 includes a shield 11345 on either side of the diamond 11315 and the electrical components associated with the diamond 11315.

[00676] Fig. 115 is a block diagram of a magnetometer with two light pipes in accordance with an illustrative embodiment. The magnetometer 11500 includes a light source 11305, a diamond 11315, two light pipes 11325 with associated shields 11345, and two photo detectors 11335. In alternative embodiments, additional, fewer, and/or different elements may be used. In the embodiment illustrated in Fig. 115, the source light 11310 from the light source 11305 passes through the diamond 11315. The light that enters the diamond 11315 can be split and can exit the diamond 11315 in two streams of modulated light 11320. In some embodiments, the two streams of modulated light 11320 are in opposite directions. In alternative embodiments, the two streams of modulated light 11320 are in any suitable orientation to one another. In some embodiments, the two streams of modulated light 11320 exit the diamond 11315 in directions orthogonal to the direction in which the source light 11310 enters the diamond 11315.

[00677] Fig. 115 illustrates a magnetometer with two light streams exiting the diamond 11315. In alternative embodiments, the magnetometer can be used with three or more light streams that exit the diamond 11315. For example, if the diamond 11315 is a cube, light can enter the diamond 11315 on one of the six sides. In such an example, up to five light streams can exit the diamond 11315 via the five other sides. Each of the five light streams can be transmitted to one of five photo detectors 11335. Using two or more light streams that exit the diamond 11315, which are sensed by associated photo detectors 11335, can provide increased sensitivity. Each of the light streams contains the same information. That is, the light streams contain the same amount of red light. Each light stream provides one of the multiple photo detectors a sample of the light. Thus, in embodiments in which multiple light streams from the diamond are used, multiple samples of the same light are gathered. Having multiple samples provides redundancies and allows the system to verify measurements. In some embodiments, the multiple measurements can be averaged or otherwise combined. The combined value can be used to determine the magnetic field applied to the diamond.

[00678] Fig. 116 is a flow diagram of a method for measuring a magnetic field in accordance with an illustrative embodiment. In alternative embodiments, additional, fewer, and/or different operations may be performed. Also, the use of a flow chart and arrows is not meant to be limiting with respect to the order or flow of operations. For example, in some embodiments, one or more of the operations can be performed simultaneously.

[00679] In an operation 11605, light is generated by a light source. Any suitable light source can be used. For example, lasers or light emitting diodes can be used. In some embodiments, sunlight or environmental light can be used as the light source. In an illustrative embodiment, the light generated by the light source is green light or blue light. In some embodiments, a filter can be used to filter out undesirable light frequencies (e.g., red light).

[00680] In an operation 11610, light from the light source is sensed. In an illustrative embodiment, the light can be sensed using a photo detector. In some embodiments, the photo detector is sensitive to electromagnetic interference. In some embodiments, the operation 11610 is not performed. For example, in some embodiments, light from the diamond is sensed and the sensed light signal is compared to a pre-determined reference value.

[00681] In an operation 11615, light from the light source is transmitted through a first light pipe. In embodiments in which light from the light source is sensed using a photo detector located between the light source and the diamond, the first light pipe can be surrounded by a material that attenuates EMI. In such embodiments, EMI from electrical components near the diamond can be attenuated via the material such that the photo detector is not affected by or is less affected by the EMI. In some embodiments, such as those in which the operation 11610 is not performed, the operation 11615 may not be performed.

[00682] In an operation 11620, light from the light source is transmitted through the diamond. In embodiments in which the operation 11615 is performed, light from the first light pipe is transmitted through the diamond. As mentioned above, the diamond can include NV centers that are affected by magnetic fields. The amount of red light emitted from the diamond (e.g., via the NV centers) can change based on the applied magnetic field.

[00683] In an operation 11625, light emitted from the diamond is transmitted through a second light pipe. In an operation 11630, light from the second light pipe is sensed. In an illustrative embodiment, the light is sensed via a light detector that is sensitive to EMI. In such embodiments, the light pipe can be surrounded by material that attenuates EMI from electrical components near the diamond, such as a Helmholtz coil or a microwave generator/modulator.

[00684] In an operation 11635, a magnetic field point is determined. In an illustrative embodiment, the magnetic field point is a vector with a magnitude and a direction. In alternative embodiments, the operation 11635 includes determining a magnitude or a direction. In embodiments in which operation 11610 is performed, the operation 11635 can include comparing the amount of green light (or any other suitable wavelength) emitted from the light source with the amount of detected red light (or any other suitable wavelength) that was transmitted through the second light pipe. In alternative embodiments, the amount of detected red light that was transmitted through the second light pipe is compared to a baseline amount. In alternative embodiments, any suitable method of determining the magnetic field point can be used.

[00685] MAGNETOMETER WITH A LIGHT EMITTING DIODE

[00686] In many instances, a light source is used to provide light to the diamond. The more light that is transmitted through the diamond, the more light can be detected and analyzed to determine the amount of red light emitted from the diamond. The amount of red light can be used to determine the strength of the magnetic field applied to the diamond. Accordingly, in some instances, lasers are used to provide light to the diamond. Lasers can provide concentrated light to the diamond and can focus the beam of light relatively easily.

[00687] However, lasers may not be the most effective light source for all applications. For example, some lasers produce polarized light. Because the axes of the NV centers may not all be oriented in the same direction, the polarized light from a laser may excite NV centers with axes oriented in one direction more effectively than NV centers with axes oriented in other directions. In instances in which sensitivity in all directions (or more than one direction) is desired, nonpolarized light may be used. The non-polarized light may affect the NV centers of different orientations (more) uniformly. In such instances, a light source such as a light-emitting diode (LED) may be used as the light source. In some instances, lasers that produce non-polarized light may be used. For example, helium-neon (HeNe) lasers can be used.

[00688] In some instances, lasers are relatively bulky and large compared to LEDs. In such instances, using LEDs as the light source for a magnetometer using a diamond with NV centers may provide a more compact and versatile sensor. In some instances, lasers user more power to produce light than do LEDs. In such instances, LEDs may allow a power source, such as a battery, to last longer, be smaller, and/or provide less power.

[00689] Fig. 117 is a block diagram of a magnetometer in accordance with an illustrative embodiment. An illustrative magnetometer 11700 includes an LED 11705, source light 11710, a diamond 11715, red light 11720, a filter 11725, filtered light 11730, a photo detector 11735, and a radio frequency transmitter 11745. In alternative embodiments, additional, fewer, and/or different elements may be used.

[00690] The LED 11705 can be used to produce the source light 11710. In alternative embodiments, any suitable light source can be used to produce the source light 11710. For example, a light source that produces non-polarized light can be used. In embodiments in which an LED is used, any suitable LED may be used. For example, the LED 11705 can emit primarily green light, primarily blue light, or any other suitable light with a wavelength shorter than red light.

[00691] In some embodiments, the LED 11705 emits any suitable light, such as white light. The light can pass through one or more filters before entering the diamond 11715. The filters can filter out light that is not the desired wavelength.

[00692] The source light 11710 is emitted by the LED 11705. The source light 11710 can be any suitable light. In an illustrative embodiment, the source light 11710 has a wavelength of between 500 nanometers (nm) and 600 nm. For example, the source light 11710 can have a wavelength of 532 nm (e.g., green light), 550 nm, or 518 nm. In some embodiments, the source light 11710 can be blue (e.g., with a wavelength as low as 450 nm). In yet other embodiments, the source light 11710 can have a wavelength lower than 450 nm. In some embodiments, the source light 11710 can be any color of visible light other than red.

[00693] An illustrative diamond 11715 includes one or more nitrogen vacancy centers (NV centers). As explained above, each of the NV centers' axes can be oriented in one of multiple directions. In an illustrative embodiment, each of the NV centers are oriented in one of four directions. In some embodiments, the distribution of NV centers with any particular axis direction is even throughout the diamond 11715. The diamond 11715 can be any suitable size.

In some embodiments, the diamond 11715 is sized such that the source light 11710 provides a relatively high light density. That is, the diamond 11715 can be sized such that all or almost all of the NV centers are excited by the source light 11710. In some instances, the LED 11705 emits less light than a laser. In such instances, a thinner diamond can be used with the LED 11705 to ensure that all or nearly all of the NV centers are excited. The diamond can be "thinner" in the direction that the source light 11710 travels. Thus, the source light 11710 travels a shorter distance through the diamond 11715.

[00694] A magnet 11740 can be used to provide a magnetic field. When the magnetic field is applied to the diamond 11715 and light is traveling through the diamond 11715, the NV centers can cause the amount of red light emitted from the diamond 11715 to be changed. For example, when the source light 11710 is pure green light and there is no magnetic field applied to the diamond 11715, then the red light 11720, which is emitted from the diamond 11715, is used as a baseline level of red light 11720. When there is a magnetic field applied to the diamond 11715, such as via the magnet 11740, the amount of red light 11720 varies in intensity. Thus, by monitoring the amount of red light from a baseline (e.g., no magnetic field applied to the diamond 11715) in the red light 11720, a magnetic field applied to the diamond 11715 can be measured. In some instances, the red light 11720 emitted from the diamond 11715 can be any suitable wavelength.

[00695] The radio frequency transmitter 11745 can be used to transmit radio waves to the diamond 11715. The amount of red light emitted from the diamond 11715 changes based on the frequency of the radio waves absorbed by the diamond 11715. Thus, by modulating the frequency of the radio waves emitted from the radio frequency transmitter 11745 the amount of red light sensed by the photo detector 11735 may change. By monitoring the amount of red light sensed by the photo detector 11735 relative to the frequency of the radio waves emitted by the radio frequency transmitter 11745, the strength of the magnetic field applied to the diamond 11715 by the magnet 11740 can be determined.

[00696] In an illustrative embodiment, a photo detector 11735 is used to receive the light emitted from the diamond 11715. The photo detector 11735 can be any suitable sensor configured to analyze light emitted from the diamond 11715. For example, the photo detector 11735 can be used to determine the amount of red light in the red light 11720.

[00697] As illustrated in Fig. 117, some embodiments include a filter 11725. The filter 11725 can be configured to filter the red light 11720. For example, the filter 11725 can be a red filter that permits red light to pass through the filter 11725 but blocks some or all of non-red light from passing through the filter 11725. In alternative embodiments, any suitable filter 11725 can be used. In some embodiments, the filter 11725 is not used. In embodiments that include the filter 11725, the red light 11720 emitted from the diamond 11715 passes through the filter 11725, and the filtered light 11730 (which is emitted from the filter 11725) travels to the photo detector 11735. In embodiments in which a filter 11725 is used, greater sensitivity may be achieved because the photo detector 11735 detects only the light of interest (e.g., red light) and other light (e.g., green light, blue light, etc.) does not affect the sensitivity of the photo detector 11735.

[00698] Fig. 118 is an exploded view of a magnetometer in accordance with an illustrative embodiment. An illustrative magnetometer 11800 includes an LED 11805, a housing 11810, a source light photo sensor 11815, a mirror tube assembly 11820, electromagnetic glass 11825, a concentrator 11830, retaining rings 11835, a diamond assembly 11840, a concentrator 11845, a modulated light photo sensor 11850, a sensor plate 11855, and a lens tube coupler 11860. In alternative embodiments, additional, fewer, and/or different elements may be used. Additionally, the embodiment illustrated in Fig. 118 is meant to be illustrative only and not meant to be limiting with respect to the orientation, size, or location of elements.

[00699] An illustrative LED 11805 includes a heat sink that is configured to dissipate into the environment heat created by the LED 11805. In the embodiment illustrated in Fig. 118, at least a portion of the LED 11805 (e.g., a cylindrical portion) fits within the housing 11810. Adjacent to the LED 11805 within the housing 11810 is the mirror tube assembly 11820. The mirror tube assembly 11820 is configured to focus the light from the LED 11805 into a concentrated beam.

[00700] The source light photo sensor 11815 is configured to receive a portion of the light emitted from the LED 11805. In some embodiments, the source light photo sensor 11815 can include a green filter. In such embodiments, the source light photo sensor 11815 receives mostly or all green light. In embodiments in which the source light photo sensor 11815 is used, the amount of green light sensed by the source light photo sensor 11815 can be compared to the amount of red light sensed by the modulated photo sensor 11850 to determine the magnitude of the magnetic field applied to the diamond assembly 11840. As discussed above, in some embodiments, the source light photo sensor 11815 may not be used. In such embodiments, the amount of red light sensed by the modulated photo sensor 11850 can be compared to a baseline amount of red light to determine the magnitude of the magnetic field applied to the diamond assembly 11840.

[00701] In some embodiments, such as those that use the source light photo sensor 11815, electromagnetic glass 11825 can be located between the source light photo sensor 11815 and the diamond assembly 11840. In some embodiments, the diamond assembly 11840 can emit electromagnetic interference (EMI) signals. In some instances, the source light photo sensor 11815 can be sensitive to EMI signals. That is, in such instances, the source light photo sensor 11815 performs better when there is less EMI affecting the source light photo sensor 11815. The electromagnetic glass 11825 can allow light to pass through the electromagnetic glass 11825, but inhibit transmission of electromagnetic signals. Any suitable electromagnetic glass 11825 can be used. In alternative embodiments, any suitable EMI attenuator can be used.

[00702] The concentrator 11830 can be configured to concentrate light from the mirror tube assembly 11820 (and/or the electromagnetic glass 11825) into a more narrow beam of light. The concentrator 11830 can be any suitable shape, such as parabolic. The diamond assembly 11840 can include a diamond with one or more NV centers. The concentrator 11830 can concentrate light from the LED 11805 into a beam of light with a cross-sectional area that is similar to the cross-sectional area of the diamond. That is, the light from the LED 11805 can be concentrated to most effectively flood the diamond with the light such that as much of the light as possible from the LED 11805 passes through the diamond and/or such that as many NV centers as possible are excited by the light. The concentrator 11830 may include a ring mount that is configured to hold the concentrator 11830 at a secure location within the housing 11810.

[00703] The diamond assembly 11840 can include any suitable components. For example, as mentioned above, the diamond assembly 11840 can include a diamond. The diamond can be located at the center of the diamond assembly 11840. The diamond assembly 11840 may also include one or more circuit boards that are configured to modulate electromagnetic signals applied to the diamond. In an illustrative embodiment, the diamond assembly 11840 includes a Helmholtz coil. For example, a three-dimensional Helmholtz coil can be used counteract or cancel unwanted magnetic fields from affecting the diamond. In an illustrative embodiment, the circuit boards or other electronics can emit EMI signals. In some embodiments, the diamond assembly 11840 includes a red filter that allows red light emitted from the diamond to pass through to the modulated photo sensor 11850. In alternative embodiments, the red filter can be located at any suitable location between the diamond and the modulated photo sensor 11850. In yet other embodiments, the red filter may not be used.

[00704] In some embodiments, the retaining rings 11835 can be used to hold one or more of the elements of the magnetometer 11800 within the housing 11810. Although Fig. 118 illustrates two retaining rings 11835, any suitable number of retaining rings 11835 may be used. In some embodiments, the retaining rings 11835 may not be used.

[00705] Similar to the concentrator 11830, the concentrator 11845 is configured to concentrate light emitted from the diamond assembly 11840 into a more narrow beam. For example, the concentrator 11830 can be configured to concentrate light into a beam that has the same or a similar cross-sectional area as the modulated photo sensor 11850. The concentrator 11845 can be configured to focus as much light as possible from the diamond assembly 11840 to the modulated photo sensor 11850. By increasing the amount of light emitted from the diamond assembly 11840 that is sensed by the modulated photo sensor 11850, the sensitivity of the magnetometer 11800 can be increased.

[00706] As mentioned above, electromagnetic glass 11825 can be located between the diamond assembly 11840 and the modulated photo sensor 11850 to shield the modulated photo sensor 11850 from EMI signals emitted from the diamond assembly 11840. The sensor plate 11855 can be used to hold the modulated photo sensor 11850 in place such that the modulated photo sensor 11850 receives the concentrated light beam from the concentrator 11845 (and/or the diamond assembly 11840). A lens tube coupler 11860 may be used as an end cap to the housing 11810, thereby holding the various elements in place inside the housing 11810.

[00707] Fig. 119 is a flow diagram of a method for detecting a magnetic field in accordance with an illustrative embodiment. In alternative embodiments, additional, fewer, and/or different operations may be performed. Also, the use of a flow diagram and arrows is not meant to be limiting with respect to the order or flow of operations. For example, in some embodiments, one or more of the operations may be performed simultaneously.

[00708] In an operation 11905, power is provided to a light emitting diode (LED). Any suitable amount of power can be provided. For example, a 5 milli-Watt (mW) LED can be used. The LED can be powered by two or more AA batteries. In alternative embodiments, the LED can use more or less power. In some embodiments, the amount of power provided to the LED is modulated based on a particular application. In some embodiments, the operation 11905 includes providing pulsed power to the LED to cause the LED to alternately lighten and darken. In such embodiments, any suitable frequency and/or pattern can be used. In alternative embodiments, the operation 11905 can include causing any suitable device to emit non-polarized light.

[00709] In an operation 11910, light emitted from the LED is sensed. Sensing the light from the LED can include using a photo detector. The operation 11910 can include determining an amount of green light emitted from the LED. In some embodiments, the operation 11910 is not performed.

[00710] In an operation 11915, light from the LED is focused into a diamond. The diamond can include one or more NV centers. The light can be focused as to excite as many of the NV centers as possible with the light from the LED. Any suitable focusing method can be used. For example, lenses or light pipes can be used to focus light from the LED to the diamond.

[00711] In an operation 11920, light from the diamond is focused to a photo detector. Light from the LED passes through the diamond, is modulated by the diamond, and is emitted from the diamond. The light emitted from the diamond is focused to a detector such that as much light emitted from the diamond as possible is detected by the photo detector. In an operation 11925, the light from the diamond is sensed by the photo detector. In an illustrative embodiment, the operation 11925 includes determining the amount of red light emitted from the diamond.

[00712] In an operation 11930, a magnetic field applied to the diamond is determined. In embodiments in which operation 11910 is performed, the amount of red light emitted by the diamond is compared to the amount of green light emitted from the LED to determine the magnetic field. In embodiments, in which operation 11910 is not performed, the amount of red light emitted from the diamond is compared to a baseline quantity of red light. In alternative embodiments, any suitable method of determining the magnetic field applied to the diamond can be used.

[00713] In an illustrative embodiment, noise in the light emitted from the LED can be compensated for. In such an embodiment, noise in the light emitted from the LED can be detected by a photo detector, such as the photo detector used for the operation 11910. Noise in the light emitted from the LED passes through the diamond and is sensed by the photo detector that senses light emitted from the diamond, such as the photo detector used for the operation 11925. In an illustrative embodiment, amount of light detected in the operation 11910 is subtracted from the light detected in the operation 11930. The result of the subtraction is the changes in the light caused by the diamond.

[00714] DIAMOND NITROGEN VACANCY SENSOR WITH DUAL RF SOURCES

[00715] Figure 120 is a schematic illustrating a portion of a DNV sensor 12000 with a dual RF arrangement in accordance with some illustrative implementations. The magnetic sensor shown in Figure 6 used a single RF excitation source 630. The DNV sensor 12000 illustrated in Figure 120 uses two separate RF elements. A top RF element 12004 and a bottom RF element 12008 are used to provide the microwave RF to the diamond 12020. As shown in Figure 120, the diamond 12020 is sandwiched between the two RF elements 12004 and 12008. A space 12006 can be used between the RF elements 12004 and 12008 to all light ingress or egress. In addition light can enter or leave the sensor via spaces 12002 and/or 12010. Accordingly, light can be shown onto the diamond 12020 from various positions and photo-sensors, such as photodiodes, can be used in various locations to collect the red light that exits the diamond 12020.

[00716] FIG. 121 is a view of an enclosed DNV sensor with a dual RF arrangement in accordance with some illustrative implementations. In this implementation, the RF elements are located on two circuit boards 12112. The diamond, not shown in Figure 121 but shown as 12320 in Figure 123, is located between the circuit boards 12112. The RF element can include one or more spiral elements with n number of loops. For example, each RF element can include a single spiral with 2, 3, 4, etc., loops. In other implementations, the RF element can include multiple spirals, such as 2, 3, 4, 5, etc., that are stack on top of one another. In these implementations, the number of loops in each spiral can be the same or can be different. For example, in one implementation, each RF element contains five spirals each having four loops. These elements can be made using fusion bonded multilayer dielectrics.

[00717] A spacer 12114 separates the individual circuit boards. The sensor assembly also includes retaining rings 12108 and a plastic mounting plate 12116. The illustrated sensor assembly is contained with a lens tube 12104 such as a 1 inch ID lens tube. The sensor assembly also contains a direct-current connector 12106 that can be used to provide power to the sensor assembly. The assembly also includes a photo sensor 12140.

[00718] In this illustrated implementation, the RF elements are fed from a RF feed cable 12102, that can be a coaxial cable. The RF feed cable 12102 attaches to the assembly via an RF connector 12110. In other implementations, a second RF feed cable can be used. In this implementation, each RF element is fed using a separate RF signal.

[00719] Figures 122A and 122B are schematics of an assembly portion of a DNV sensor with a dual RF arrangement in accordance with some illustrative implementations. The illustrated assembly portion can be used in the implementation illustrated in Figure 121. Figure 122A illustrates one side of the assembly. This side includes an ingress portion 12202 that allows light to reach the diamond that is between the RF elements. In this implementation, the ingress portion is in the center of the assembly. In other implementations, the ingress portion can be located between the RF elements along the diameter of the assembly.

[00720] Figure 122B illustrates the opposite side of the assembly shown in Figure 122A. The circuit board elements that contain the RF elements 12214 are shown along with the space 12212 that separates the RF elements. A RF connector 12210 is shown that provides the RF source signal to the RF elements. A photo sensor 12240 is also shown in the middle of the assembly. Underneath the photo sensor is an egress portion. As light is shined through the ingress portion 12220, the light will pass through the diamond, not shown, that is contained within the assembly between the two RF elements. The light will pass through the diamond and exit the opposite side of the assembly and reach the photo sensor 12240. The photo sensor can then measure property of the light, such as the light's wavelength.

[00721] Figure 123 is a cross-section of a portion of a DNV sensor with a dual RF arrangement in accordance with some illustrative implementations. The portion of the DNV sensor is the same as the portion of the assembly illustrated in Figures 122A and 122B and can be used in the DNV sensor illustrated in Figure 121. The cross section of the sensor assembly is done as illustrated on the portion of the assembly 12330. The diamond 12320 is now visible as located between a top RF element 12304 and a bottom RF element 12308. A spacer 12310 separates the RF elements 12304 and 12308. The ingress portion of the assembly is shown directly above the diamond 12320. Light can enter the assembly through this ingress portion and pass through the diamond 12320. The light that exits the diamond can pass through the egress portion of the assembly and reach the photo sensor 12340. Additional egress portions through the space can also be used. Thus, light can be collected from the face of the diamond and/or through the edges of the diamond.

[00722] As noted above, the RF elements can be fed by separate RF feeds and light can be collected from various faces and/or edges of the diamond. Figure 124 is a schematic illustrating a DNV sensor with a dual RF arrangement in accordance with some illustrative implementations. The DNV sensor includes a light source and focusing lens assembly 12402. The light source can various light sources such as a laser or LED. In Figure 124, the light source is an LED. A heatsink 12408 is used to bleed away the heat from the light source. The DNV assembly is housed in an element structure 12406 and described in greater detail below. In the illustrated implementation, the element structure 12460 is fixed within the sensor. As this implementation includes separate RF feeds, two RF cables 12404 are provided to the DNV assembly. The RF signal provided to the RF elements can therefore be the same or the feed signals can be different. In some implementations, the RF signals are different based upon the configuration of the elements of the NV diamond assembly. For example, if one RF element is slightly further from the NV diamond compared to the other RF element, different RF signals can be used to take into account the differences in distances.

[00723] Figure 125 is a cross-section of a DNV sensor of Figure 124 with a dual RF arrangement in accordance with some illustrative implementations. Accordingly, the DNV sensor includes a light source heatsink 12508. In addition, elements within the light source and focusing lens assembly and element structure can be seen. The light source and focusing lens assembly includes an LED 12502 and one or more focusing lenses 12504. Light from the LED 12502 is focused, using the one or more focusing lenses 12504, onto an NV diamond 12520. In this implementation, light enters an edge of the NV diamond 12520 and is ejected from one or more faces on the NV diamond 12520. In Figure 125, light is ejected from both the top and bottom faces of the NV diamond 12520. Accordingly, there are two photo-sensor assemblies 12540 and 12542 located above and below the NV diamond. These photo-sensor assemblies 12540 and 12542 can include photodiodes that detect the light that is ejected from the NV diamond 12520.

[00724] The NV diamond is located between two RF elements 12530 and 12532. These RF elements provide a microwave RF signal uniformly across the NV diamond. Light is ejected through the top and bottom face of the NV diamond 12520 and travels to one of the photo-sensor assemblies 12540 and 12542. Between the photo-sensor assemblies 12540 and 12542 there are attenuators 12534. The attenuators reduce or eliminate the RF generated by the RF elements to avoid interference with other elements of the sensor. Ejected travels through a light pipe 12536 that is between each photo-sensor assembly and the NV diamond. In various implementations, at least a portion of the light pipe is located within the attenuators. Such a configuration allows the photo-sensing array to be positioned closer to the NV diamond and remain unaffected by the EMI of the sensor. Further description of the benefits of housing a portion of the light pipe within an attenuator is described in U.S. Patent Application No. / ,_, entitled "Magnetometer with Light Pipe," filed on the same day as this application, the contents of which are hereby incorporated by reference.

[00725] Figure 126 is a schematic illustrating a DNV sensor with a dual RF arrangement and laser mounting in accordance with some illustrative implementations. In the illustrated implementation, the light source has been changed to a laser which is included in a laser and focusing lens assembly 12602. In the illustrated implementation, the NV diamond is housed in an adjustable structure. A rotatable adjustment assembly 12604 allows the NV diamond to be rotated. An x-y-z adjustment assembly 12606 allows the NV diamond and various elements to be positioned in 3D space. As the NV diamond's position can be changed, there is an x-y adjustment assembly 12604 that is used to adjust the ingress of light into the NV diamond assembly.

[00726] Figure 127 is a cross-section of a DNV sensor illustrated in Figure 126 with a dual RF arrangement and laser mounting in accordance with some illustrative implementations. An NV diamond 12720 is located between two RF elements 12732. Light pipes 12730 provide a path for light that exits the faces of the NV diamond 12720 to travel from the NV diamond to one of two photo-sensing assemblies 12740. In various implementations, at least a portion of each light pipe 12730 is housed with an attenuator 12734. In other implementations, the DNV sensor does not contain the attenuators 12734. The rotatable adjustment assembly allows the NV diamond and related elements such as the RF elements to be rotated within the NV diamond assembly.

This can allow the light ingress portion of the diamond to be altered as well as altering where light exiting the NV diamond 12720 is collected. For example, the NV diamond can be rotated to allow light to enter the diamond at an edge or at a face.

[00727] The x-y-z adjustment assembly allows the position of the NV diamond and related elements within the NV diamond assembly to be changed. This assembly allows for the control of where the light will enter the NV diamond as well as where the ejected light will be collected. The x-y adjustment assembly allows the light source to also be moved such that the light can enter the NV diamond assembly regardless of the rotation and position of the NV diamond within the NV diamond assembly.

[00728] Figures 128A and 128B are schematics of an assembly portion of a DNV sensor with a dual RF arrangement in accordance with some illustrative implementations. Figure 128A illustrates one side of the assembly portion of the DNV sensor and Figure 128B illustrates the opposite side of the assembly. In the illustrated implementation, there are two light egress portions 1280 and 12810. These portions allow ejected light to leave the assembly and be detected by photo element. The assembly includes two RF elements, a top RF element 12804 and a bottom RF portion 12806. These RF elements can be fed using the same RF signal or can be fed separate RF signals via the RF connector 12802 and RF connector 12812. The NV diamond is not shown, but is located between the RF elements 12804 and 12806. Light from the light source enters the diamond via a space between the RF elements 12804 and 12806. Light is ejected from the NV diamond via either light egress portion 12808 and 12810.

[00729] Figures 129A and 129B are schematics of an assembly portion of a DNV sensor with a dual RF arrangement in accordance with some illustrative implementations. Figures 129A and 129B further illustrate the assembly portion of the DNV sensor illustrated in Figures 128A and 128B. The NV diamond 12920 is now shown located within a spacer or a diamond alignment plate, such as a plastic diamond alignment plate. In the illustrated implementation, light enters between the RF elements. For example, light can enter the diamond via the light ingress portion 12910 of the assembly. The RF elements 12902 and 12904 are shown in Figure 129A along with the RF feed cable connectors 12906 and 12908.

[00730] REDUCED INSTRUCTION SET CONTROLLER FOR DIAMOND

NITROGEN VACANCY SENSOR

[00731] Following below are more detailed descriptions of various concepts related to, and implementations of, methods, apparatuses, and systems for providing synchronous control of multiple RF signals and digital output signals for magnetometry, such as for a diamond nitrogen vacancy (DNV) sensor. The subject technology can provide the synchronous control with controlled, single-cycle timing requirements for a flexible and sensitive DNV magnetometry. In some implementations, the disclosed system includes a reduced instruction set (RISC) processor that is coupled to a configurable signal synthesizer. The configurable signal synthesizer may be configured to perform single-cycle commands for frequency shifts, digital outputs, and initial synchronous preprocessing of received data such that the digital control, acquisition, and waveform generation may be performed on the same clock cycle for synchronization. The specially designed single-cycle operations of the subject technology may provide more precise and deterministic timing for digital control, acquisition, and waveform generation. In some implementations, the RF waveform generation and digital control outputs are coordinated in configurable patterns that can range from simple sequences to complex adaptive control patterns.

[00732] FIG. 130 is a block diagram depicting an overview of an implementation of a singlecycle synthesis, control, and acquisition system 13000. The system 13000 is configured to control multiple RF signals and digital output signals for magnetometry, such as for a diamond nitrogen vacancy (DNV) sensor. In some implementations, the system 13000 may be implemented as a field-programmable gate array (FPGA) or may be implemented as an application specific integrated circuit (ASIC). The system 13000 is implemented as a single single-cycle integrated circuit for RF waveform synthesis, digital control, and acquisition. A more detailed implementation of the single-cycle synthesis, control, and acquisition system is shown as the system 13100 in FIG. 131.

[00733] The system 13000 includes a host interface 13010 that receives DNV sensing information from an external system, such as a data processing or acquisition system (not shown), and is communicatively coupled to a program counter 13020, a program memory 13030, and an acquisition processor 13080. The host interface 13010 may be coupled to a data processing system, such as system 13200 of FIG. 132, that can communicate with the system 13000 via the host interface 13010. Thus, the data processing system can output instructions, such as control instructions from the reduced instruction set, to the system 13000 via the host interface 13010 for the program memory 13030. The data acquisition system can also receive output from the acquisition processor 13080 via the host interface 13010, such as pulse processed data from a DNV sensor. Thus, the host interface 13010 provides communication between the components of the system 13000 and an external system. A more detailed depiction of the host interface 13010 is shown as host interface 13110 in FIGS. 131 and 132A. The host interface 13010 is communicatively coupled to the program counter 13020, which is in communication with the program memory 13030 and the jump control 13070. A more detailed implementation of the program counter 13020 is shown as program counter 13120 in FIGS. 131 and 132B. A more detailed implementation of the program memory 13030 is shown as program memory 13130a, 13130b in FIGS. 131 and 132C. A more detailed implementation of the jump control 13070 is shown as jump control with delay 13140a and the jump control 13140b in FIGS. 131 and 132D-E. The program memory 13030 provides outputs through a decoder 13040 to a RF waveform generator of the CORDIC (Coordinate Rotation Digital Computer) synthesis 13050 for generating the RF waveform to be applied, the digital control 13060 for controlling a laser on/off timing, and a jump control 13070. The jump control 13070 provides feedback to the program counter 13020.

[00734] The CORDIC synthesis 13050 provides digital up or down conversion and can have a run-time configurable base frequency and increment for the RF waveform generation. The RF waveform generator of the CORDIC synthesis 13050 utilizes a frequency base value and a frequency increment that outputs a single value for a slope of a ramp that is used by an accumulator to generate a sine wave for the RF waveform. The sine wave is processed through an upconverter to generate the RF waveform signal to be applied to the magnetometry component, such as a DNV sensor. In some implementations, the CORDIC synthesis 13050 may phase shift the RF waveform. For instance, an analog or digital switch may be used for arbitrary waveform generation. A more detailed implementation of the RF waveform generator and CORDIC synthesis 13050 is shown as RF waveform generator 13150 in FIGS. 131 and 132F.

[00735] The digital control 13050 provides timing control for a number of aspects of a magnetometry component, such as a DNV sensor. The digital control 13050 includes RF gating or switches and may include additional general inputs or outputs for additional control. The digital control 13050 may output signals to control the activation of a magnetometry component, such as a laser for exciting a nitrogen vacancies of a DNV sensor. The digital control can also convert the CORDIC output to 0 via a multiplexer (MUX) such that no RF signal is applied to the DNV sensor. In some implementations, the digital control 13050 can be used for an acoustooptic modulator (AOM) to control optic pulsing of the laser and/or can be used for phase shift control. The digital control 13050 may further provide an output to an I/Q component, such as a digital I/Q. A more detailed implementation of the digital control 13060 is shown as digital control 13160 in FIGS. 131 and 132G.

[00736] The acquisition processor 13080 provides initial synchronous preprocessing of data received from a magnetometry component, such as data received from a photo detector of a DNV sensor. The acquisition processor 13080 can include two coherent channels for simultaneous collection of data, such as the collection of red light, infrared, laser, etc. data. In some implementations, the channels may be chainable up to four. In an implementation with a photo detector, data received by the acquisition processor 13080 may be at a rate of 50 MHz, 100 MHz, 200 MHz, or greater. To reduce the amount of data transferred to an external system from the system 13000, the acquisition processor can preprocess the data to reduce the size of the data outputted. Thus, in some implementations, the acquisition processor 13080 synchronously gathers samples from a magnetometry component, such as the photo detector of a DNV sensor, and preprocesses the data, such as decimation of the data. In some implementations, the acquisition process 13080 may include a digital output to trigger an accumulator for a predetermined number of clock cycles and then will subtract from two integration windows for processing of the data. By providing a consistent trigger based on a single-cycle of the system 13000, the preprocessing of the acquired data can be more consistent, thereby increasing sensitivity and reducing noise in the acquired data from inconsistent triggers. In some implementations, the acquisition processor 13080 may include a digitally controllable offset for effects similar to a DC block or AC coupling. A more detailed implementation of the acquisition processor 13080 is shown as acquisition processor 13170 in FIGS. 131 and 132H.

[00737] In the implementation shown, the system 13000 is configured for single-cycle instructions for the components of the system 13000 such that the RF waveform generator of the CORDIC synthesis 13050 for generating the RF waveform, the digital control 13060 for controlling the laser on/off timing, and the acquisition processor 13080 operate on the same clock cycle. A main counter (not shown) drives the RF waveform generation while the program counter 13020 allows for delays to be implemented for the digital control 13050 and the acquisition processor 13080. The single-cycle can provide laser and/or microwave deterministic timing control for coordination of the CORDIC synthesis 13050, the digital control 13060, and the acquisition processor 13080. Thus, the single-cycle tightly ties in the digital control 13060 for controlling the laser and acquisition processor with the RF waveform generation of the CORDIC synthesis 13050. The single-cycle permits synchronous stepped-frequency complex waveform synthesis by the CORDIC synthesis 13050 and permits coordinated large-range frequency retuning (e.g., >1 GHz) without losing base time. The single-cycle system 13000 can also provide synchronous reduced instruction set program control of the frequency for the RF waveform synthesis. The system 13000 of FIG. 130 with a single-cycle also reduces redundant components compared to systems that utilize separate components for the RF waveform generator, digital control, and/or acquisition processor. In some implementations, the singlecycle synthesis, control, and acquisition system 13000 may also be configured for two-cycle implementations as well.

[00738] The system 13000 can utilize a reduced instruction set (RISC) engine that issues one instruction per clock cycle, including for conditional branching. In some implementations, the reduced instruction set can include commands for an unconditional jump (jmp), a conditional jump (cjmp), setting of a loop counter (setc < counter value ), setting of a frequency (self < frequency value>), setting of a digital control output field (seta <outputfield value>), a frequency increment (incf <increment value>), and a delay for a specified cycle count {del <cycle count value>).

[00739] As a comprehensive system that exercises parameter variation, the single-cycle synthesis, control, and acquisition system 13000 can provide lock-step precision for laser on/off timing via the digital control 13060, sequenced microwave waveform synthesis and delivery via the RF waveform generator and CORDIC synthesis 13050, data acquisition via the acquisition processor 13070, and laser and /or microwave deterministic timing control. The single-cycle synthesis, control, and acquisition system 13000 can facilitate effective experimentation by enabling rapid coordination of excitation signals and tuning across broad frequency ranges without losing timing. Not all of the depicted components may be required, however, and one or more implementations may include additional components not shown in the figure. Variations in the arrangement and type of the components may be made, and additional components, different components, or fewer components may be provided.

[00740] As noted above, FIG. 131 is a circuit diagram illustrating an example implementation of the single-cycle synthesis, control, and acquisition system 13100. In one or more implementations, the single-cycle synthesis, control, and acquisition system 13100, as implemented by the circuit of FIG. 131, is a dedicated hardware configured for DNV applications that are customized to the unique requirements of controlling multiple, diverse instruments and sensors across the RF to optical domain. The reduced instruction set (RISC) engine is configured to issue one instruction per clock cycle, even for conditional branches. The RF waveform generator uses a run-time configurable base frequency and increment to provide the CORDIC synthesis with an RF waveform for digital up/down conversion. The digital control block is responsible for providing laser timing, RF gating, and additional general control input/output (I/O). The acquisition processor block is configured to provide two coherent channels (potentially chainable up to 4) for simultaneous red, infra-red (IR), laser, and other types of light collection. The acquisition processing block is further configured to synchronously collect samples and to provide digitally controllable analog offset that allows effects like DC blocking or AC coupling.

[00741] Examples of advantageous features of the single-cycle synthesis, control, and acquisition system 13100 include, but are not limited to, single-cycle deterministic timing coordination of RF waveform generation, laser control, and data acquisition, synchronous stepped-frequency for complex waveform synthesis, synchronous RISC program control of frequency, coordinated large-range (e.g., >lGHz) frequency retuning without losing time base, and a minimal instruction set.

[00742] By providing a small-scale or single chip, single-cycle synthesis, control, and acquisition system 13000, 13100 for use in magnetometry, the system 13000, 13100 can be incorporated into a variety of settings and configurations where DNV magnetometers are employed. Examples of applications of the single-cycle synthesis, control, and acquisition system 13000, 13100 include, but are not limited to incorporating the single chip into a DNV sensor, incorporating the single chip into DNV-based geolocation systems, incorporating the single chip into DNV anomaly detection systems, incorporating the single chip into covert communications systems, incorporating the single chip into distributed measure point systems, incorporating the single chip into small form factor unmanned systems for air (e.g., unmanned air vehicle (UAV), micro unmanned air vehicle (pUAV), missiles), sea, underground, and surveillance (e.g., satellites, cluster satellites, etc.), incorporating the single chip into low SWAP (size, weight, and power) applications, and utilizing the single chip, single-cycle synthesis, control, and acquisition system 13000, 13100 for automatic experimental optimization.

[00743] FIG. 132 is a diagram illustrating an example of a system 13200 for implementing some aspects of the subject technology. The system 13200 includes a processing system 13202, which may include one or more processors or one or more processing systems. A processor can be one or more processors. The processing system 13202 may include a general-purpose processor or a specific-purpose processor for executing instructions and may further include a machine-readable medium 13219, such as a volatile or non-volatile memory, for storing data and/or instructions for software programs. The instructions, which may be stored in a machine-readable medium 13210 and/or 13219, may be executed by the processing system 13202 to control and manage access to the various networks, as well as provide other communication and processing functions. The instructions may also include instructions executed by the processing system 13202 for various user interface devices, such as a display 13212 and a keypad 13214. The processing system 13202 may include an input port 13222 and an output port 13224. Each of the input port 13222 and the output port 13224 may include one or more ports. The input port 13222 and the output port 13224 may be the same port (e.g., a bi-directional port) or may be different ports.

[00744] The processing system 13202 may be implemented using software, hardware, or a combination of both. By way of example, the processing system 13202 may be implemented with one or more processors. A processor may be a general-purpose microprocessor, a microcontroller, a Digital Signal Processor (DSP), an Application Specific Integrated Circuit (ASIC), a Field Programmable Gate Array (FPGA), a Programmable Logic Device (PLD), a controller, a state machine, gated logic, discrete hardware components, or any other suitable device that can perform calculations or other manipulations of information.

[00745] A machine-readable medium can be one or more machine-readable media. Software shall be construed broadly to mean instructions, data, or any combination thereof, whether referred to as software, firmware, middleware, microcode, hardware description language, or otherwise. Instructions may include code (e.g., in source code format, binary code format, executable code format, or any other suitable format of code).

[00746] Machine-readable media (e.g., 13219) may include storage integrated into a processing system such as might be the case with an ASIC. Machine-readable media (e.g., 13210) may also include storage external to a processing system, such as a Random Access Memory (RAM), a flash memory, a Read Only Memory (ROM), a Programmable Read-Only Memory (PROM), an Erasable PROM (EPROM), registers, a hard disk, a removable disk, a CD-ROM, a DVD, or any other suitable storage device. Those skilled in the art will recognize how best to implement the described functionality for the processing system 13202. According to one aspect of the disclosure, a machine-readable medium is a computer-readable medium encoded or stored with instructions and is a computing element, which defines structural and functional interrelationships between the instructions and the rest of the system, which permit the instructions’ functionality to be realized. Instructions may be executable, for example, by the processing system 13202 or one or more processors. Instructions can be, for example, a computer program including code for performing methods of the subject technology.

[00747] A network interface 13216 may be any type of interface to a network (e.g., an Internet network interface), and may reside between any of the components shown in FIG. 132 and coupled to the processor via the bus 13204.

[00748] A device interface 13218 may be any type of interface to a device and may reside between any of the components shown in FIG. 132. A device interface 13218 may, for example, be an interface to an external device (e.g., USB device) that plugs into a port (e.g., USB port) of the system 13200. In some implementations, the device interface 13218 may be the host interface of FIG. 130, where at least some of the functionalities of the apparatus of FIG. 130 are performed by the processing system 13202.

[00749] RECOVERY OF THREE DIMENSIONAL MAGNETIC FIELD FROM A MAGNETIC DETECTION SYSTEM

Axes of the Diamond Crystal Lattice [00750] In deriving the total magnetic field vector impinging on the system 600 from the measurements obtained by the intensity response produced by the NV diamond material 620, it is desirable to establish the orientation of the axes of the diamond lattice of the NV diamond material 620 to allow for the accurate recovery of the magnetic field vector and maximize signal-to-noise information. However, as discussed above, the NV diamond material 620 may be arbitrarily oriented and, thus, have axes in an unknown orientation. Thus, in such a case, the controller 680 may be configured to compute an accurate estimation of the true orientation of the NV diamond lattice, which can be performed on-site as a calibration method prior to use. This information can be subsequently used to accurately recover the full vector information of an unknown external magnetic field acting on the system 600.

[00751] To begin, a desired geospatial coordinate reference frame relative to the system 600 by which measurement of the total magnetic field vector will take place is established. As shown in FIGS. 133A and 133B, a Cartesian reference frame having (x, y, z}orthogonal axes may be used, but any arbitrary reference frame and orientation may be used. FIG. 133A shows a unit cell 13300 of a diamond lattice having a “standard” orientation. The axes of the diamond lattice will fall along four possible directions. Thus, the four axes in a standard orientation relative to the desired coordinate reference frame may be defined as unit vectors corresponding to:

(bl)

[00752] For simplicity, the four vectors of equation (bl) may be represented by a single matrix As, which represents the standard orientation of the unit cell 13300: = [as,l as,2 as,3 a5,4] (b2) [00753] The angle between axis i and axis j may also be given by the (i,j)th row of the following:

(b3) [00754] FIG. 133B is a unit cell 13300’ that represents an arbitrarily placed NV diamond material having unknown axes orientation with respect to the coordinate reference frame. By defining the standard orientation matrix As with reference to the established coordinate reference frame, the arbitrary orientation shown in FIG. 133B may be obtained through a rotation and/or reflection of the standard orientation matrix. This can be achieved by applying a transformation matrix R, which is defined as a general 3x3 matrix representing the three-dimensional, orthogonal Cartesian space and is, at this stage, unknown. The transformation matrix may be used to obtain our desired matrix A as follows: A = RAS (b4)

Deriving the Total Magnetic Field Vector [00755] As described above with reference to FIGS. 3-5, the total magnetic field acting on the system 600 may be measured fluorescently. These measurements may be modeled as a linear system from which the total magnetic field impinging on the sensor may be determined: m = | ATb + n\ (b5) [00756] Here, b E M3xl represents the magnetic field vector acting inside the sensor system, expressed in Cartesian coordinates relative to the coordinate reference frame; ATb represents the projection of the magnetic field vector onto each of the four, arbitrarily-placed NV center diamond lattice axes; η E R4xl represents the sensor noise vector; and m E R4xl represents the measurement vector, where the ith element represents the estimated projection of the magnetic field onto the sensor axis t. In terms of units, it is assumed that the measurement vector has been converted from the DNV sensor’s native units (in terms of microwave resonance frequency) into the units of magnetic field strength. Furthermore, the term \ATb + n\ represents the element-wise absolute value of ATb + n, rather than its determinant.

[00757] Given the linear model for the magnetic field measurement of equation (b5) a least squares estimate of the total magnetic field acting on the system 600 may be given by:

(b6) [00758] In the above equation, the + superscript denotes the Moore-Penrose pseudoinverse. Because the three four-element columns of AT are linearly independent, equation (b6) may be rewritten as:

(b7) rji 4 [00759] In equation (b7), ASAS = -/(established in more detail below) has been substituted. Because R is an orthogonal matrix, equation (b7) can be reduced to:

(b8) [00760] In equations (b7)-(b8), it was assumed that all the measurements were weighted equally. If, however, some of the axes have less variance in their measurements or are preferred for other reasons, then different weightings may be used for each of the axes for a more optimal least squares estimate. If w E R4xl represents the positive weights for each of the measurements and W = diag(w), then the weighted least-squares formulation for the total magnetic field may be written as:

(b9) [00761] Based on equation (b9), the generalized least squares solution of equation (b6) may now be written as:

(t* 10) [00762] For a perfect NV diamond material 620 having no defects (e.g., lattice misalignments, impurities, etc.) and no sensor noise, b should be equal to b. However, in an imperfect system, it is possible to utilize a performance metric to determine the error associated with the measurement. One possible metric that may be used is a 2-norm of the residual vector minimized by the least squares solution. This metric γ may be given by:

(bll)

[00763] Because the residual vector is proportional to the measurement amplitude, the magnitude of the true magnetic field may be used to normalize the metric to give a consistent metric even in the presence of a changing true magnetic field:

(hi 2) [00764] If the true magnetic field is not known, the measurement vector magnitude may be used to normalize the metric:

(b 13)

Estimation of Absolute Axes’ Orientation in the NV Diamond Material [00765] By simple substitution of equation (4) into equation (5), the measurement obtained by the system 600 may be represented in terms of the standard orientation matrix:

(t* 14) [00766] As described above, a permanent magnet (e.g., the first magnetic field generator 670) and/or coils (e.g., the second magnetic field generator 675) may be used to adequately separate out the Lorentzian dips that correspond to the magnetic field measurements along each diamond axis. However, at this point, the orientations of the sensor’s axes are unknown. Thus, the required bias or control magnetic field, defined as bbias, that will produce the desired dip separation is unknown.

[00767] As will be described in more detail below, there exists a plurality of bbias vectors that can equally separate out the four Lorentzian dips for adequate measurement purposes.

Moreover, for the purposes of determining the unknown orientation of the diamond lattice, it is not necessary to precisely place or apply the bias magnetic field that will result in perfectly equal dip separation, which may be more appropriate during field measurement of an external magnetic field. In this case, any bbias vector that sufficiently separates the four dips may suffice for the determination of the unknown orientation of the diamond lattice, thus increasing the viable bbiasvectors appropriate for this step. Sufficient spectral dip separation, however, may depend on the width of the dips and the planned magnitude of the calibration magnetic fields (described below). The width of the dips varies, depending on diamond composition and sensor laser and/or RF excitation mechanisms. Based on the resulting widths due to inherent sensor characteristics, the magnitude and orientation should be sufficient to ensure that the anticipated maximum spectral shifts that will occur due to the calibration tests will maintain sufficient separation between neighboring Lorentzian dips.

[00768] FIG. 134 shows a step for determining a viable bbias vector field. As shown in FIG. 134, the first magnetic field generator 670 may be arbitrarily placed in one or more positions and/or orientations such that multiple magnetic fields are applied to the diamond having an unknown orientation 13300’. Measurements of the fluorescence intensity response are taken for each position and/or orientation of the first magnetic field generator 670. Once a fluorescence intensity response 13400 is produced that adequately separates out the four Lorentzian pairs, the position of the first magnetic field generator 670 is maintained and the process may proceed to calibration tests. In other embodiments, the separation process may be performed by the second magnetic field generator 675. In this case, the controller 680 may be configured to control the second magnetic field generator 675 to generate multiple magnetic fields until the desired separation is produced. In yet other embodiments, the first and/or second magnetic field generators may be affixed to a pivot assembly (e.g., a gimbal assembly) that may be controlled to hold and position the first and/or second magnetic field generators to a predetermined and well-controlled set of orientations, thereby establishing the desired Lorentzian separation and/or calibration magnetic fields (described below). In this case, the controller 680 may be configured to control the pivot assembly having the first and/or second magnetic field generators to position and hold the first and/or second magnetic field generators at the predetermined orientation.

[00769] After an appropriate calibration bbias field has been found that adequately separates out the four Lorentzian dips, a measurement vector mbias of the corresponding bias magnet’s magnetic field projections is collected. The measurement vector may be expressed in a similar manner as the linear model described in equation (b5):

(b 15) [00770] As noted above with regard to equation (b5), the variables represented in equation (b 15) are the same, but represented in relation to the applied bias field.

[00771] At this point, it is unknown which of the four Lorentzian dips correspond to which of the sensor axes, which still remain unknown. However, because any possible permutation of the axes’ ordering can be captured by applying an appropriate orthogonal matrix to As, and, because the process described herein is estimating the orthogonal matrix that best represents the data, any permutation of the axes’ ordering will be compensated by the transformation. Due to this, the axes may be generally assigned such as, for example, the Lorentzian dip that is closest to the zero-field splitting frequency is assigned as ax, the second-closest is assigned as a2, and so on.

Sign Recovery of Magnetic Field Projections [00772] Due to the symmetry of the sensor measurements, the obtained mbias vector has no inherent sign information for each of its four components. However, sign information may be recovered using the following process.

[00773] The projections of the magnetic field vector onto the four axes is given by the vector ATb. The sum of the projections may then be initially presumed to equal zero per the following:

(t* 16) [00774] In the above equation (b 16), 0 e R4xl represents a vector consisting of all zeros. If the sum of the elements of a vector x E M4xl equals zero, then a magnetic field vector b may be found whose projections onto the four axes of a diamond is identical to x. In this regard, the magnetic field vector b may be defined as follow:

(hi 7)

[00775] The projection of the magnetic field vector b onto the four axes of a diamond may be given by: (b 18) [00776] The values for the As matrix from equations (1)-(2) may be plugged into equation (b 18) to give:

(hi 9) [00777] Because it was initially assumed that the sum of all the elements of x equals 0, equation (bl9) can be reduced to:

(b20) [00778] Thus, a b vector exists whose projections onto the axes of a diamond is identical to x and the initial presumption of equation (b 16) is proved. Accordingly, the sum of the axes’ projections of any magnetic field impinging on a diamond will be equal to zero, and measurements obtained, in the absence of noise, will sum to zero as well. Thus, sign information for the bias measurements may be recovered following this basic principle. This particular step is especially applicable if the bias magnetic field’s projections are much larger than the expected noise levels.

[00779] With reference to FIG. 135, a method to recover sign information from the bias field measurements according to one embodiment will now be described. First, in a step 13510, the largest of the four measurements is arbitrarily set to a sign value, either positive or negative.

Once this is chosen, the next steps are dictated based on this sign choice such that the principles of equation (bl6) are maintained. For example, as shown in the embodiment of FIG. 134, the largest of the four measurements, measurement 13410a, is assigned as positive. Next, in a step 13511, the second-largest measurement (e.g., measurement 13410b shown in FIG. 134) is set to negative. By setting the second-largest measurement to negative, the positive value assigned to the largest measurement may be offset toward zero. In a step 13512, the third-largest measurement (e.g., measurement 13410c of FIG. 134) is assigned a negative sign value.

Because, by definition, the second-largest measurement is smaller than the largest measurement, a negative sign value for the third-largest measurement will offset the largest measurement further towards zero. Finally, in a step 13513, the smallest measurement is assigned either a positive or negative value that allows for the sum total of the four measurements to approximately equal zero. In FIG. 134, the smallest measurement 13410d is assigned a positive value. After this process, therefore, an appropriately signed mbias vector may be obtained.

[00780] After application of the bias field that cleanly separates out the four Lorentzian dips and a measurement of the resulting bias field has been collected, a series of calibration tests may be performed. As shown in FIG. 135, a series of p known external magnetic fields, in conjunction with the fixed bbias field, is applied and the resulting sensor measurements are collected. In some embodiments, a series of at least three p (p > 3) weak magnetic fields are applied. In particular embodiments, at least three non-coplanar p weak magnetic fields are applied. In yet other embodiments, three orthogonally spaced p (p > 3) weak magnetic fields are applied. In particular embodiments, four to five p (p = 4, 5,...) weak magnetic fields are applied. Such fields may be applied by the second magnetic generator 675 and, thus, controlled by the controller 680. The known applied external magnetic fields may be represented by the following matrix:

(b21) [00781] In equation (b21), bk represents the kth field for k = 1 ... p. The obtained measurements mk corresponding to each bk may be represented by the linear model described above as:

(b22) [00782] The portion of mk that corresponds solely to the external magnetic field bk can be isolated, along with proper sign values, by:

(b23) [00783] In the above equation, ° represents the Hadamard (i.e., element-wise) matrix product, while sgn( ) represents the element-wise signum function. At this stage, AT remains unknown. However, ATbbias may be estimated. This is possible by substituting rhbias for ATbbias in equation (23):

(b24) [00784] Combining equations (22) and (23), the derived calibration measurement can be written as follows:

(b25) [00785] In the above equation (b25), nk = nk ° sgn(mbias) + nbias.

[00786] By defining the matrices M = [fh1 m2 ... inp] and N= [r^ n2 ... np],the external magnetic fields and their corresponding measurements may be compactly represented by:

(b26) [00787] Once the known B and the measured M have been obtained, equation (b26) may be expanded as follows:

(b27) [00788] From equation (bl9),

was demonstrated and thus substituted into equation (b27) above. Because the singular values of As are known and equal (i.e., about 1.15), the noise term N will not be colored or largely amplified in the expression

Thus, we can treat the expressior

as a new noise term:

(b28) [00789] Combining equations (27) and (28) results in:

(b29) [00790] Taking the transpose of both sides of equation (29) gives:

(b30) [00791] In the next step, an orthogonal matrix R is desired that provides the least-squares fit between BT and

in equation (b30). Some least-squares formulations may introduce translation and/or angular error into the orthogonal matrix R. For example, error may be introduced when applying the matrix R to the standard orientation matrix As in the form of a translation of the center of the axes from the standard orientation to the estimated orientation or in a change in the angles shown in equation (b3) between given axes. Thus, a least-squares fit that can substantially maintain the relative orientation of the axes to each other when rotating from the standard orientation to the estimated orientation is preferable. In this regard, the orthogonal matrix may be expressed as:

(b31) [00792] Where, in equation (b31), 0(3) represents the group of orthogonal 3x3 matrices and || ||F represents the Frobenius norm.

[00793] By defining the orthogonal matrix R as above, the particular problem may be reduced to the Orthogonal Procrustes Problem to solve for R. First, the following is defined:

(b32) [00794] A singular devalue decomposition of Z is performed to obtain:

(b33) [00795] Where in equation (b33), U is an orthogonal 3x3 matrix that contains the left singular vectors of Z; Σ is an orthogonal 3x3 matrix that contains the singular values of Z; and VT is an orthogonal 3x3 matrix that contains the right singular vectors of Z. Given the above, the solution to the Orthogonal Procrustes Problem of (b33) is given by:

(b34) [00796] Accordingly, with equation (b34), an estimate R is obtained that may be applied to the standard orientation matrix A5to give the true axes orientation matrix A. Thus, an estimate A of A can be obtained by applying equation (b4) to yield:

(b35) [00797] In the embodiment described above, the Orthogonal Procrustes Problem provides an advantage in reducing translation and/or angular error that may be introduced by the least-squares fit and, thus, provides an accurate estimation of the needed rotation matrix. By accurately estimating the rotation matrix, an accurate estimation of the orientation of an arbitrarily placed lattice structure in a magnetic field detection system having a magneto-optical defect center material is produced. This, in turn, reduces the process to determining the orientation of a diamond in the magnetic detection system 600 to a simple calibration method that may be calculated and controlled by the controller 680 and performed before sensing begins, without the need for pre-manufacturing processes to orient the lattice structure relative to the sensor or additional equipment for visual aid inspection. Moreover, with the above, an accurate estimate of the true orientation of the axes of the NV diamond material 620 may be obtained and recovery of the external magnetic field for magnetic sensing, described further below, may be improved.

[00798] Once the axes have been determined using embodiments described above, the bias magnet’s magnetic field can subsequently be optimally re-oriented using the methods described below along with the newfound knowledge of the axes’ orientations.

Application of the Bias Magnetic Field [00799] Once the orientation of the axes of the diamond lattice has been determined, a bias magnetic field may be applied to cleanly separate out the Lorenztian dips and obtain sign estimates of the magnetic field projections onto the identified diamond lattices.

[00800] As noted above, the baseline set of microwave resonance frequencies is defined as those frequencies which are created when no external magnetic field is present. When no bias magnet or bias coil is present (i.e., no bias magnet or bias coil is added internally to the system by, for example, the first and second magnetic field generators 670, 675), the baseline resonance frequencies will be identical for all four diamond axes (e.g., all approximately equal to 2.87 GHz). If a bias magnet or coil is introduced (e.g., applied by the first magnetic field generator 670 and/or second magnetic generator 675), the four axes’ baseline resonance frequencies may be uniquely shifted if the projection of the bias magnet’s magnetic field onto each of the four axes is unique. By applying a known bias magnetic field, the magnitude and orientation of a non-zero external magnetic field may then be determined by evaluating the additional shift in each axis’ microwave resonance frequency relative to the baseline frequency offset, which will be described in more detail below.

[00801] For an external magnetic field in the absence of a bias magnetic field, the Lorentzian dips in the microwave resonance spectra that correspond to each of the four axes may overlap significantly. Such overlap can occur when either the projection of the external field onto multiple axes is similar, or when the width of the Lorentzian dips is much larger than the difference in the resonance frequency shifts due to the external magnetic field. In these cases, an external bias magnet applied as part of the system 600 may be used to minimize the overlap by significantly separating the Lorentzian spectral dips, thereby enabling unique recovery of the external magnetic field projections on each of the axes.

[00802] The following will describe how an optimal bias magnetic field via the first magnetic field generator 670 (e.g., a permanent magnet) and/or the second magnetic field generator 675 (e.g., three-axis Helmholtz coil system) is calculated by the controller 680 according to one embodiment. Once the optimal bias magnetic field is determined, the orientation of the bias magnet’s magnetic field relative to the diamond may then be determined to produce the desired baseline shifts.

[00803] Similar to above when determining the orientation of the axes of the diamond lattice, the magnetic field generated by the bias magnet (e.g., the first magnetic field generator 670 and/or the second magnetic field generator 675) may be represented by the vector bbias e R3xl. As noted above, the projection of the bias magnetic field onto each of the four axes of the diamond is given by ATbbias. The shifted baseline set of microwave resonance frequencies / relative to the centered zero-field splitting frequency (e.g., about 2.87 GHz) may be given by:

(b36) [00804] In equation (b36), it is noted that γ represents the nitrogen vacancy gyromagnetic ratio of about 28 GHz/T.

[00805] Depending on the characteristics of the sensor and its particular application, optimum performance of the sensor may be achieved under different sets of baseline frequencies.

However, not all arbitrary baseline frequency sets may be realizable. Thus, the criteria for producing baseline offsets may be determined from which the corresponding required bias field may be computed.

[00806] First, / may be defined to represent the desired baseline set of microwave resonance frequencies relative to the centered zero-field splitting frequency and be expressed as follows:

(b37) [00807] Using equation (b36), if a bbias exists that produces /, then the projections of bbias onto the four axes of the diamond may be given by:

(b38) [00808] Regardless of the sign value of the axis projection (i.e., whether positive or negative), the same pair of microwave resonance frequencies {—ft, ft} will be produced by the system 600. Thus, there is freedom to choose whether each axis projection will be positive or negative without affecting the resulting baseline.

[00809] To confirm whether a bbias actually exists that produces /, the concept that a bias field bbias will exist only if the projections of bbias onto the four diamond axes sum to zero is applied, which was shown above as true in equations (bl6)-(b20). Thus, this concept may be expressed as:

(b39) [00810] Accordingly, if a set {s^ s2, s3, s4) can be found that causes the sum in equation (b39) to be zero, a bbias vector will exist that produces the desired baseline /. From equation (bl7) above, bbias may then be given by:

(b40) [00811] Once that set {s^ s2, s3, s4) has been determined that results in a bbias vector that produces the desired baseline /, the Lorentzian dips may be fine-tuned to a desired separation by applying the appropriate bias field using the first magnetic field generator 670 and/or the second magnetic field generator 675. For example, equal separation between each pair of adjacent dips in the microwave resonance spectra may be represented by the following baseline set:

(b41) [00812] The above equation holds for any ctEl. The separation between any pair of adjacent dips is 2a. In addition, a possible set {s-^ s2, s3, s4) that results in the sum of projections summing to zero is {1, — 1, — 1,1}. Thus, from equations (b40) and (b41), the bbias that will produce an equally separated baseline set is given by:

(b42) [00813] Assuming that the diamond is in a standard orientation with respect to the coordinate reference frame (i.e., A = A5), equation (b42) will reduce to:

(b43) [00814] Alternatively, however, the bbias may also be determined after the true axes orientation has been estimated using the methods described above. For example, the bbias that will produce an equally separated baseline set for an arbitrarily orientated diamond will be given by substitution of equation (b35) into equation (b42) to yield:

(44) [00815] Maximum separation or a single axis pair of dips in the microwave resonance spectra may also be achieved. The maximum separation may be represented by the following baseline set: f = {±a, ±a, ±a, ±3 a,} (b45) [00816] The above equation holds for any ctEl. The separation between the primary pair and the three other peak pairs of adjacent dips will be 2a. As described above, a possible set {s-l, s2, s3, s4) that results in the sum of projections summing to zero is {—1, -1,-1,1). Thus, from equations (40) and (45), the bbias that will produce a maximum single dip separated baseline set is given by:

(b46) [00817] Assuming that the diamond is in a standard orientation with respect to the coordinate reference frame (i.e., A = A5), equation (b46) will reduce to:

(b47) [00818] It should be noted that equation (b47) corresponds directly to one of the four axis orientations, a4.

[00819] Alternatively, the bbias may also be determined after the true axes orientation has been estimated using the methods described above. For example, the bbias that will produce a maximum separated baseline set for an arbitrarily orientated diamond will be given by substitution of equation (b35) into equation (b46) to yield:

(b48)

Measuring an External Magnetic Field [00820] Once a bias magnet and/or coil with a known bias magnetic field has been applied to the system 600 using the first and/or second magnetic field generators 670, 675 to produce a desired baseline set of microwave resonance frequencies, the magnitude and direction of an external magnetic field may be measured. By defining the external magnetic field at the location of the diamond sensor as bext E R3xl, equation (b5) may be expressed as:

(b49) [00821] The portion of m that corresponds to the external magnetic field may be isolated by comparing m to the known projections of the bias magnetic field bbias, which can be expressed as:

(b50) [00822] In equation (b50), ° denotes the Hadamard (element-wise) matrix product. The resulting mext will have the appropriate sign for the projection of bext onto each axis, thereby allowing unambiguous recovery of bext using the approach shown in equations (b5)-(b 13), where mext is used in place of m to estimate bext.

[00823] Based on the above, an unknown external magnetic field vector may be accurately estimated and recovered. FIG. 137 shows a flowchart illustrating a method for the recovery of an external magnetic field vector as implemented by the controller 680 of the system 600 using the methods described above. In a step 13710, the bias magnetic field that will produce the desired separation between the Lorentzian responses for each diamond axis is computed using the methods described above (e.g., equal separation or maximum separation computations).

Once this is determined, the first magnetic field generator 670 (e.g., a permanent magnet) may be positioned to produce the desired field or the second magnetic field generator 675 (e.g., three-axis Helmholtz coil) may be controlled by the controller 680 to generate the desired field. Next, in a step 13720, a relative direction (i.e., sign value) is assigned to each Lorentzian pair using the sign recovery method described above and shown in FIG. 135.

[00824] Once the Lorentzian responses have been optimally separated by the application of an appropriate bias field and sign values of the pairs have been assigned, measurement data of the total magnetic field impinging on the system 600 is collected in a step 13730. Then, in a step 13740, shifts in the Lorentzian dips due to the external magnetic field are detected and computed based on the linear relationship between the application of the magnetic field vector projected on a given diamond axis and the resulting energy splitting between the ms = -1 spin state and the ms = +1 spin state. In a step 13750, this shift information is then used along with the methods described using equations (b49)-(b50) to compute an estimate of the external magnetic field ^ext- [00825] The embodiments of the inventive concepts disclosed herein have been described in detail with particular reference to preferred embodiments thereof, but it will be understood by those skilled in the art that variations and modifications can be effected within the spirit and scope of the inventive concepts.

[00826] MAGNETIC BAND-PASS FILTER

[00827] Following below are more detailed descriptions of various concepts related to, and implementations of, methods, apparatuses, and systems for providing filtering for signals in magnetic communications and anomaly detection using diamond nitrogen-vacancy (DNV) sensors. The subject technology provides a band-pass filter that allows users to focus on particular frequency signals for anomaly detection and an operating frequency band that permits limited environment noise for communication. A filtered signal increases signal-to-noise (SNR) for communications and anomaly detection. The filtered signal has reduced unwanted signals and allows the operator to better interpret the signal. Magnetic communication using a magnetic medium presents advantageous features for ground penetrating applications and underwater environments. A limitation to the application of the magnetic communications is the noisy operational environment. The disclosed technology addresses this issue by providing suitable magnetic filtering.

[00828] In some implementations, a system of the subject technology attenuates magnetic communication signals outside of a targeted frequency region. In the electrical world, band-pass filters may be realized using a combination of resistors and capacitors and/or other passive or active elements. In the magnetic world, however, solenoids and diamagnetic material can be employed to perform the desired filtering functions.

[00829] FIG. 138 overview diagram of a diamond 13802 having a nitrogen vacancy of a DNV sensor 13800 with a low pass filter 13810 and a high pass filter 13820. As shown in FIG. 138, the low pass filter 13810 and high pass filter 13820 cooperate to form a magnetic band-pass filter. The low pass filter 13810 is formed by a solenoid that uses the diamond 13802 as a core and includes a resistor 13812 and a loop of conductive material 13814 looped about a portion of the diamond 13802. In some implementations, the loop 13814 of conductive material may include a plurality of loops about the diamond 13802. The resistor 13812 is electrically coupled to a first end of the loop 13814 and a second end of the loop 13814. In some implementations, the resistor 13812 is a constant resistor. In other implementations, the resistor 13812 may be a variable resistor, such as a potentiometer or other tunable resistor element. With a variable resistor, a modification of the resistance can selectively attenuate a set of high frequency magnetic signals. That is, for instance, a modification to a resistance applied by a potentiometer can modify the upper frequency that is attenuated by the low pass filter 13810. Thus, higher frequency magnetic signals can be attenuated to reduce the noise relative to an expected signal to be detected by the DNV sensor 13800. The solenoid formed by the loop 13814 and resistor 13812 resists changing magnetic fields and generates opposing fields proportional to the rate of change of the changing magnetic field, which has a greater effect on alternating magnetic fields. In some implementations, the solenoid formed by the loop 13814 and the resistor 13812 may include a capacitor to control the shape of the low pass filter 13810.

[00830] The high pass filter 13820 is formed by a diamagnetic material 13822 positioned relative to the diamond 13802. The diamagnetic material 13822 is repelled by an external magnetic field as the diamagnetic material 13822 generates an induced magnetic field that aligns anti-parallel to an applied environmental magnetic field. Based on the selected diamagnetic material 13822, the low frequency for magnetic signals that are filtered out can be changed. In some implementations, the diamagnetic material 13822 may have a magnetic permeability of approximately 0.9. The diamagnetic material 13822 may act as a DC blocker to filter out low frequency magnetic signals emitted from DC current or devices.

[00831] Using the combination of the diamagnetic material 13822 as a high pass filter 13820 and one or more solenoids as low pass filters 13810, a band pass filter may be formed for the DNV sensor 13800. If the low pass filter 13810 includes a tunable resistor 13812, then the attenuation of an alternating magnetic field can be optimized for a desired frequency band. That is, varying the resistance for the low pass filter 13810 can vary the high frequency magnetic signals that are attenuated while the high pass filter 13820 filters the low frequency magnetic signals.

[00832] FIG. 139 is a graphical diagram 13900 depicting an example magnetic signal 13902 that includes a test signal 13904 without utilizing filtering. The magnetic signal 13902 corresponds to the use of a DNV-sensor-based equipment deployed in a vehicle being driven in a rural area with a manageable magnetic noise floor. The equipment was used to read magnetic signals while the vehicle that a DNV sensor is deployed on was very noisy. This combined with the proximity to the equipment makes it difficult to recover the test signal 13904 from the noise of the example magnetic signal 13902. Given the noise of the magnetic signal 13902, providing a filtering mechanism to remove and/or reduce magnetic signal noise may increase the signal-to-noise ratio (SNR) to provide better clarity when receiving a particular signal of interest, such as the test signal 13904.

[00833] FIG. 140 depicts a diamond 14002 of a DNV sensor 14000 with a low pass filter 14010 and showing a magnetic field 14050 of the environment, a change 14052 in the magnetic field of the environment, and an induced magnetic field 14054 by the low pass filter to filter high frequency signals. In the arrangement shown, the diamond 14002 operates as the core of a solenoid made up of a loop of conductive material 14012 and a resistor 14014 that acts as the low pass filter 14010. The diamond 14002 is exposed to an external magnetic field 14050, B. When external magnetic field 14050, B, is then changed by a change in the magnetic field 14052, ΔΒ, such as based on external magnetic noise from the environment, then the change in magnetic field 14052, ΔΒ, causes the solenoid to induce a current 14016 in the conductive material 14012 proportional and opposite to the rate of change of the magnetic field 14052 according to the Lenz law (EMF = -N ΔΦ/Δΐ), where ΔΦ is the change in magnetic flux, Δΐ is the incremental change in time, N is the number of turns of the conductive material 14012 about the diamond 14002, and EMF is the induced electro-magnetic force (EMF). The induced current 14016 due to the generated EMF has a greater effect on high frequency magnetic signals, due to the derivative term ΔΦ/Δΐ, and the effect can be tuned by both the number of turns, N, in the conductive material 14012 and the resistance provided by the resistor 14014. In some implementations, a variable resistor 14014 can be used to change the operating region of the low-pass filter 14010. In some implementations, the variable resistor 14014 may be a potentiometer. In some implementations, the variable resistor 14014 may be coupled to a first end of a loop of the conductive material 14012 and a second end of the loop of the conductive material 14012 to form the low pass filter 14010. In some implementations, the solenoid formed by the loop of conductive material 14012 and the resistor 14014 may include a capacitor to control the shape of the low pass filter 14010.

[00834] In some implementations, a controller may be coupled to the variable resistor 14014 and/or to a component for adjusting the variable resistor 14014. For instance, a digital potentiometer may be used as the variable resistor 14014 and a controller may be configured to modify a resistance of the variable resistor 14014. In some implementations, as described in greater detail herein, the controller may be configured to modify a resistance of the variable resistor 14014 to selectively attenuate the low-pass filter 14110. The selective attenuation may be responsive to a strength and/or orientation of a detected magnetic disturbance or magnetic signal.

[00835] In other implementations, the controller may be configured to modify an orientation of the DNV sensor 14000. For instance, the DNV sensor 14000 may be mounted to a structure to allow for modification of a rotational orientation of the DNV sensor 14000 in one or more directions. For instance, the DNV sensor 14000 may be mounted to a printed circuit board (PCB) or other suitable structure that can be mechanically or otherwise rotated in one or more directions. The modification of the orientation of the DNV sensor 14000 may be responsive to a strength and/or orientation of a detected magnetic disturbance or magnetic signal.

[00836] FIG. 141 depicts a diamond 14102 of a DNV sensor 14100 with a first low pass filter 14110 and a second low pass filter 14120. In the arrangement shown, the diamond 14102 operates as the core of a first solenoid of the first low pass filter 14110 made up of a first loop of conductive material 14112 and a first resistor 14114 and as the core of a second solenoid of the second low pass filter 14120 made up of a second loop of conductive material 14122 and a second resistor 14124. In some implementations the first loop and/or second loop can be made from several loops of conductive material. In the implementation shown, the first loop of conductive material 14112 is positioned in a first plane relative to the diamond 14102 and the second loop of conductive material 14122 is positioned in a second plane relative to the diamond 14102 such that the first and second planes are orthogonal. Thus, the first low pass filter 14110 is a low pass filter for a first spatial orientation and the second low pass filter 14120 is a low pass filter in a second spatial orientation. In some implementations, the first solenoid formed by the first loop of conductive material 14112 and the first resistor 14114 and/or the second solenoid formed by the second loop of conductive material 14122 and the second resistor 14124 may include a capacitor to control the shape of the low pass filter 14110, 14120.

[00837] If the first resistor 14114 and second resistor 14124 have the same resistance, then the attenuation from the low pass filters 14110, 14120 is strongest at the diagonal between the first low pass filter 14110 and second low pass filter 14120 due to the induced EMF. If the first resistor 14114 has a greater resistance than the second resistor 14124, then the attenuation from the low pass filters 14110, 14120 will be stronger nearer to the first plane within which the first low pass filter 14110 is positioned than the second planed within which the second low pass filter 14120 is positioned. In some implementations, the first resistor 14114 and/or second resistor 14124 can be variable resistors. In some implementations, the first variable resistor 14114 and/or the second variable resistor 14124 may be a potentiometer. In some implementations, the first resistor 14114 may be coupled to a first end of the first loop of the conductive material 14112 and a second end of the first loop of the conductive material 14112 to form the first low pass filter 14110. The second resistor 14124 may be coupled to a first end (e.g., a third end) of the second loop of the conductive material 14122 and a second end (e.g., a fourth end) of the second loop of the conductive material 14122 to form the second low pass filter 14120.

[00838] The first variable resistor 14114 can be used to independently change the operating region of the first low-pass filter 14110 and the second variable resistor 14124 can be used to independently change the operating region of the second low-pass filter 14120. The independent change of the operating region of the low pass filters 14110, 14120 can modify the spatial orientation of the maximum attenuation, thereby providing modifying the spatial orientation of the maximum attenuation due to the induced EMF. Thus, in some implementations, a controller may be coupled to the first variable resistor 14114 and/or to a component for adjusting the first variable resistor 14114 and the second variable resistor 14124 and/or a component for adjusting the second variable resistor 14124 to modify the spatial orientation of the maximum attenuation relative to the diamond 14102. For instance, a digital potentiometer may be used as the first variable resistor 14114 and/or second variable resistor 14124 and a controller may be configured to modify a resistance of the first variable resistor 14114 and/or second variable resistor 14124.

In some implementations, as described in greater detail herein, the controller may be configured to modify a resistance of the first variable resistor 14114 and/or second variable resistor 14124 to selectively attenuate the first low-pass filter 14110 and/or second low pass filter 14120. The selective attenuation may be responsive to a strength and/or orientation of a detected magnetic disturbance or magnetic signal. In some implementations, a modification to the first variable resistor 14114, such as a potentiometer, attenuates a set of high frequency magnetic signals for the first low pass filter 14110 for the first spatial orientation. A modification to the second variable resistor 14124, such as a potentiometer, attenuates a set of high frequency magnetic signals for the second low pass filter 14120 for the second spatial orientation.

[00839] In some further implementations, the diamond 14102 operates as the core of a third solenoid of a third low pass filter made up of a third loop of conductive material and a third resistor. In some implementations the third loop can be made from several loops of conductive material. The third loop of conductive material may be positioned in a third plane relative to the diamond 14102 such that third plane is orthogonal to the first plane of the first low pass filter 14110 and the second plane of the second low pass filter 14120. Thus, the third low pass filter is a low pass filter for a third spatial orientation. The third resistor may be coupled to a first end (e.g., a fifth end) of the third loop of the conductive material and a second end (e.g., a sixth end) of the third loop of the conductive material to form the third low pass filter The third resistor may be a variable resistor, such as a potentiometer. In some implementations, a modification to the third variable resistor attenuates a set of high frequency magnetic signals for the third low pass filter for the third spatial orientation. The third low pass filter, third resistor, third loop, etc. may be further constructed and/or used in a similar manner to the first low pass filter 14110, first resistor 14114, first loop 14112, etc. as described above except that the third low pass filter is positioned in the third spatial orientation. Thus, with the first low pass filter 14110, second low pass filter 14120, and third low pass filter, a variation of the resistances applied to each variable resistor can modify the spatial orientation of the maximum attenuation relative to the diamond 14102.

[00840] In any of the DNV sensors 13800, 14000, 14100 described herein, a diamagnetic material, such as diamagnetic material 13822, may be utilized for a high pass filter, as will be described in greater detail herein.

[00841] FIG 142 depicts a diamond 14202 of a DNV sensor 14200 relative to a diamagnetic material 14210 and showing alignment of the poles 14212 of the diamagnetic material 14210 relative to the induced magnetic field 14220. The diamagnetic material 14210 is repelled by an external magnetic field, B, and the diamagnetic material 14210 generates an induced magnetic field, Bl, that aligns anti-parallel to an applied environmental magnetic field.

[00842] FIG. 143 depicts the behavior of a diamagnetic material for use in a high pass filter relative to an external or applied environmental magnetic field, B. The curve 14300 depicts the variation of magnetism, M, of a diamagnetic material versus the external or applied environmental magnetic field, B. As shown in FIG. 143, the magnetism of the diamagnetic material is opposite to the applied magnetic field and includes a delay until a constant magnetic field for the diamagnetic material is achieved. The delay is due to the diamagnetic material, such as diamagnetic material 14210, having regions, such as poles 14212 that align anti-parallel to the external magnetic field and require some amount of time to realign opposite to the external magnetic field. These effects, however, may not be instantaneous and the diamagnetic material experiences a charging time similar to a charging time of a capacitor. Thus, high frequency magnetic signals spend less time in an orientation than slow modulating signals. This allows a high-frequency portion of a magnetic signal to pass through the diamagnetic material while a low-frequency portion of the magnetic signal is filtered. The magnetic permeability and the size of the diamagnetic material can vary the effect.

[00843] Referring back to FIG. 142, based on the selected diamagnetic material 14210, the low frequency for magnetic signals that are filtered out can be changed. In some implementations, the diamagnetic material 14210 may have a magnetic permeability of approximately 0.9. The diamagnetic material 14210 may act as a DC blocker to filter out low frequency magnetic signals emitted from DC current or devices. In some implementations, the diamagnetic material 14210 may be positioned at an end of the diamond 14202. In some implementations, the diamagnetic material 14210 may be positioned at an end of the diamond 14202 based on the position of one or more current or expected DC currents or devices relative to the DNV sensor 14200. In other implementations, the DNV sensor 14200 may be rotated to align the diamagnetic material 14210 relative to the current or expected DC currents or devices. In other implementations, multiple diamagnetic materials 14210 may be positioned about the diamond 14202. For instance, a pair of diamagnetic materials 14210 may be positioned at opposing ends of the diamond 14202 of the DNV sensor 14200. Further still a diamagnetic cube of material may be formed about the DNV sensor 14200. In still further implementations, the diamagnetic material 14210 may be a liquid material and the diamond 14202 of the DNV sensor 14200 may be positioned within the liquid diamagnetic material 14210 or otherwise surrounded by the diamagnetic material 14210.

[00844] FIG. 144 depicts a method 14400 for modifying a filtering frequency of a low pass filter for a DNV sensor based on a detected magnetic field. The method 14400 includes providing a diamond nitrogen vacancy sensor (block 14402). The DNV sensor may be any of the DNV sensors 13800, 14000, 14100, 14200. In some implementations, the DNV sensor may be similar to DNV sensor 14000 and may include a diamond having a nitrogen vacancy and a low pass filter. The low pass filter may include a loop of conductive material positioned about the diamond and a variable resistor coupled to a first end of the loop and a second end of the loop. In other implementations, the DNV sensor may be similar to DNV sensor 14100 and may include a diamond having a nitrogen vacancy, a first low pass filter in a first spatial orientation, and a second low pass filter in a second spatial orientation. The first low pass filter may include a first loop of conductive material positioned about a first portion of the diamond and a first variable resistor coupled to a first end of the first loop and a second end of the first loop. The second low pass filter may include a second loop of conductive material positioned about a second portion of the diamond and a second variable resistor coupled to a first end (e.g., a third end) of the second loop and a second end (e.g., a fourth end) of the second loop. The first loop of conductive material may positioned within a first plane, and the second loop of conductive material may be positioned in a second plane. In some implementations, the first plane and second plane are orthogonal. In some implementations, the first variable resistor and/or the second variable resistor is a potentiometer. In some further implementations, the DNV sensor may further include a third loop of conductive material positioned about a third portion of the diamond such that the third loop of conductive material is positioned in a third plane. The third plane may be orthogonal to the first plane and second plane. In still further implementations, either of the DNV sensors 14000, 14100 may include a diamagnetic material, such as diamagnetic material 14210 described herein.

[00845] The method 14400 further includes detecting an interfering magnetic signal (block 14404). Detecting of the interfering magnetic signal may include detecting the interfering magnetic signal with the DNV sensor. In some implementations, the detection of the interfering magnetic signal is performed with a controller in electric communication with the DNV sensor.

In other implementations, detecting the interfering magnetic signal may be with another component in electric communication with the controller. The detecting of the interfering magnetic signal may simply include detecting an orientation of magnetic signals above a predetermined high frequency.

[00846] The method 14400 further includes modifying a value for one or more of the first variable resistor or the second variable resistor based on the detected magnetic signal (block 14406). The modification of the value for the first variable resistor and/or the second variable resistor may be performed by the controller. In some implementations, the controller may include instructions to modify a digital potentiometer for the first variable resistor and/or second variable resistor. In other implementations, the controller may modify another component to modify a value for the resistance of the first variable resistor and/or second variable resistor. Modifying the resistance value for the first variable resistor and/or second variable resistor to a zero or substantially zero resistance value may result in attenuating substantially all high frequency magnetic signals.

[00847] In some implementations, one or more low pass filters may be tuned based on attenuating substantially all high frequency magnetic signals and adjusting the resistance value of the variable resistor until a test signal is detected or setting the resistance value of the variable resistor to a minimum attenuation and increasing the attenuation until a predetermined frequency value for filtering is achieved.

[00848] FIG. 145 is another method 14500 for modifying an orientation of a DNV sensor with a low pass filter based on a detected magnetic field. The method 14500 includes providing a diamond nitrogen vacancy sensor (block 14502). The DNV sensor may be any of the DNV sensors 13800, 14000, 14100, 14200. In some implementations, the DNV sensor may be similar to DNV sensor 14000 and may include a diamond having a nitrogen vacancy and a low pass filter. The low pass filter may include a loop of conductive material positioned about the diamond and a variable resistor coupled to a first end of the loop and a second end of the loop. In other implementations, the DNV sensor may be similar to DNV sensor 14100 and may include a diamond having a nitrogen vacancy, a first low pass filter in a first spatial orientation, and a second low pass filter in a second spatial orientation. The first low pass filter may include a first loop of conductive material positioned about a first portion of the diamond and a first variable resistor coupled to a first end of the first loop and a second end of the first loop. The second low pass filter may include a second loop of conductive material positioned about a second portion of the diamond and a second variable resistor coupled to a first end (e.g., a third end) of the second loop and a second end (e.g., a fourth end) of the second loop. The first loop of conductive material may positioned within a first plane, and the second loop of conductive material may be positioned in a second plane. In some implementations, the first plane and second plane are orthogonal. In some implementations, the first variable resistor and/or the second variable resistor is a potentiometer. In some further implementations, the DNV sensor may further include a third loop of conductive material positioned about a third portion of the diamond such that the third loop of conductive material is positioned in a third plane. The third plane may be orthogonal to the first plane and second plane. In still further implementations, either of the DNV sensors 14000, 14100 may include a diamagnetic material, such as diamagnetic material 14210 described herein.

[00849] The method 14500 further includes detecting a magnetic signal (block 14504). Detecting of the magnetic signal may include detecting the magnetic signal with the DNV sensor. In some implementations, the detection of the magnetic signal is performed with a controller in electric communication with the DNV sensor. In other implementations, detecting the magnetic signal may be with another component in electric communication with the controller. The detecting of the magnetic signal may simply include detecting an orientation of magnetic signals above a predetermined high frequency.

[00850] The method 14500 further includes modifying an orientation of the loop of the DNV sensor based on the detected magnetic signal (block 14506). The modification of the orientation of the loop of the DNV sensor may be performed by the controller. Modification of the orientation of the loop of the DNV sensor may include modifying an orientation of the DNV sensor itself and/or may modify the orientation of the loop independent of the orientation of the diamond of the DNV sensor. In some implementations, the controller may include instructions to modify an orientation of the DNV sensor and/or loop and DNV sensor through mechanical components, such as a servo, an actuator, etc.

[00851] MAGNETIC WAKE DETECTOR

[00852] In some aspects of the present technology, methods and configurations are disclosed for detecting small magnetic fields generated by moving charged particles. For example, fast moving charged particles moving through the Earth's atmosphere create a small magnetic field that can be detected by the disclosed embodiments. Sources of charged particles include fast moving vehicles such as missiles, aircraft, supersonic gliders, etc. To detect the small magnetic fields, highly sensitive magnetometers (e.g., DNV sensors) may be used. DNV sensors can provide 0.01 ?T sensitivity. These magnetometers can be as or more sensitive than the superconducting quantum interference device (SQUID) magnetometer (e.g., with femto-Tesla level measurement sensitivity).

[00853] As another example of a source of charged particles, a jet engine can create ions as a byproduct of the combustion process. Another example includes a super-sonic glider that generates a plasma field as the glider moves through the atmosphere. This plasma field can generate charged particles. The disclosed detectors can also detect magnetic fields underwater. Accordingly, torpedoes that are rocket propelled may create an ion flux. The charged particles, e.g., ions, are moving quite fast for a period of time until slowed down by the surrounding air. These fast moving ions (charged particles) can generate a low-level magnetic field in the atmosphere. This field can be detected by one or more detectors as described here within.

[00854] The subject technology can be used as an array of sensitive magnetic sensors (e.g., DNV sensors) to detect the magnetic fields created by charged particle sources, such as jet engine exhaust. A single detector can be used to detect the magnetic field that are generated over the detector. In one implementation, the range of a detector is 10 kilometers or less. In another implementation, the range of the detector is one kilometer. In this implementation, a single detector can detect a magnetic field within its 10 kilometer slant range. In another implementation, the magnetic sensors may be spread out along a coast or at a distance from some other areas of interest (e.g., critical infrastructure such as power plants, military bases, etc.). In addition, multiple lines of sensors can be used to allow the system to establish the missile trajectory. In one or more implementations, data from the magnetic sensors may be used in conjunction with data from passive acoustic sensors (e.g., to hear the signature whine of a jet engine) to improve the overall detection capabilities of the subject system. In some aspects, the sensors can be small enough to be covertly placed near an enemy air field to provide monitoring of jets as they take off or land (e.g., are at low altitudes). In various implementations, the detectors can be low power and persistent (e.g., always watching - without a manned crew).

These detectors, therefore, can be used for covert (e.g., passive) surveillance based on the subject solution which cannot be detected, even by current stealth technology.

[00855] Figure 146 illustrates a flying object 14602 at low altitude 14608 in accordance with some illustrative implementations. The flying object 14602 can be a cruise missile, an aircraft, or a super-sonic glider. The flying object 14602 can readily avoid radar tracking due to high clutter caused by terrain 14606 and being stealth. Even airborne radars may not be able to detect and track these objects because of intense clutter issues involved with scanning down toward the Earth and trying to track a small, stealthy target. For example, high flying surveillance radar (e.g., AW ACS or Hawkeye) can sometimes detect cruise missiles, but it is costly and has to be up in the air and have sufficient signal-to-noise ratio(SNR) to be able to operate in a high-clutter situation. Short-range radars may also provide detection capability, but require substantial power and, due to the low flight height of the missile, may be able to see the missile for an extremely brief period. The limited window of view-ability allows the missile to be easily missed by a ground based system (especially if rotating) in part because it would not persist in the field of view long enough to establish a track. The subject technology utilizes high sensitivity magnetic sensors, such as DNV sensors to detect weak magnetic fields generated by the fast movement of ions in the jet exhaust of cruise missiles. For example, a DNV sensor measures the magnetic field that acts upon the DNV sensor. When used on Earth, the DNV sensor measures the Earth's magnetic field, assuming there are no other magnetic fields affecting the Earth's magnetic field. The DNV measures a magnetic vector that provides both a magnitude and direction of the magnetic field. When another magnetic field is within range of the DNV sensor, the measured field changes. Such changes indicate the presence of another magnetic field.

[00856] When using a DNV sensor, each sample is a vector that represents the magnetic field affecting the DNV sensor. Accordingly, using measurements over time the positions in time and therefore, the path of an object can be determined. Multiple DNV sensors that are spaced out can also be used. For example, sensed magnetic vectors from multiple DNV sensors that are measured at the same time can be combined. As one example, the combined vectors can make up a quiver plot. Analysis, such as a Fourier transform, can be used to determine the common noise of the multiple measures. The common noise can then be subtracted out from various measurements.

[00857] One way measurements from a single or multiple DNV sensors can be used is to use the vectors in various magnetic models. For example, multiple models can be used that estimate the dimensions, mass, number of objects, position of one or more objects etc. The measurements can be used to determine an error of each of the models. The model with the lowest error can be identified as most accurately describing the objects that are creating the magnetic fields being measured by the DNV sensors. Alterations to one or more of the best models can then be applied to reduce the error in the model. For example, genetic algorithms can be used to alter a model in an attempt to reduce model error to determine a more accurate model. Once an error rate of a model is below a predetermined threshold, the model can help identify how many objects are generating the sensed magnetic fields as well as the dimensions and mass of the objects.

[00858] If the flying object 14602 uses a combustion engine, exhaust 14604 will be generated. The exhaust 14604 can include charged particles that are moving at high speeds when exiting the flying object 14602. These charged particles create a magnetic field that can be detected by the described implementations. As the Earth has a relatively static magnetic field, the detectors can detect disturbances or changes from the Earth's static magnetic field. These changes can be attributed to the flying object 14602.

[00859] Figure 147 illustrates a magnetic field detector in accordance with various illustrative implementations. A sensor 14706 can detected a magnetic field 14704 of a flying object 14702 passing overhead the sensor 14706. The sensor 14706 can be passive in that the sensor 14706 does not emit any signal to detect the flying object 14702. Accordingly, the sensor 14706 is passive and its use is not detectable by other sensors. For example a magnetic sensor such as a DNV-based magnetic sensor can detect magnetic field with high sensitivity without being detectable. A sensor network formed by a number of nodes equipped with magnetic sensors (e.g. DNV sensors) can be deployed, for example, along national borders, in buoys off the coast or in remote locations. For instance, a distant early warning line can be established near the Arctic Circle.

[00860] Figures 148a and 148b illustrate a portion of a detector array in accordance with various illustrative implementations. Detectors 14802 and 14804 can both detect the magnetic field generated by the flying object 14806. Given an array of detectors located in a region, data from multiple detectors can be combined for further analysis. For example, data from the detectors 14802 and 14804 can be combined an analyzed to determine aspects such as speed and location of the flying object 14806. As one example, at a first time shown in Figure 148a, detector 14802 can detect the magnetic field generated from the flying object 14806. Detector 14804 may not be able to detect this magnetic field or can detect the field but given the further distance the detected field will be weaker compared to the magnetic field detected by detector 14802. This data from a single point of time can be used to calculate a position of the object 14806. Data from a third detector can also be used to triangulate the position of the flying object 14806. Data from a single detector can also be useful as this data can be used to detect a slant position of the flying object 14806. The combined data can also be used to determine a speed of the flying object 14806.

[00861] In addition, data from one or more detectors over time can be used. In Figure 148b, the flying object 14806 has continued its path. The magnetic field detected by detector 14804 has increased in strength as the flying object approaches detector 14804, while the magnetic field detected by detector 14802 will be weaker compared to the magnetic field detected in Figure 148a. The differences in strength are based upon the flying object being closer to detector 14804 and further away from detector 14802. This information can be used to determine a trajectory of the flying object 14806.

[00862] As describe above, data from a single detector can be used to calculate a slant range of a flying object. The slant range can be calculated based upon a known intensity of the magnetic field of the flying object compared with the intensity of the detected field. Comparing these two values provides an estimate for the distance that the object is from the detector. The precise location, however, is not known, rather a list of possible positions is known, the slant range. The speed of the flying object can be estimated by comparing the detected magnetic field measurements over time. For example, a single detector can detect the magnetic field of the flying object over a period of time. How quickly the magnetic field increases or decreases in intensity as the flying object move toward or away, respectively, from the detector can be used to calculate an estimate speed of the flying object. Better location estimates can also be used by monitoring the magnetic field over a period of time. For example, monitoring the magnetic field from the first detection to the last detection from a single detector can be used to better estimate possible positions and/or the speed of the flying object. If the magnetic field was detected for a relatively long period of time, the flying object is either a fast moving object that flew closely overhead to the detector or is a slower moving object that few further away from the detector.

The rate of change of the intensity of the magnetic field can be used to determine if the object is a fast moving object or a slow moving object. The possible positions of the flying object, therefore, can be reduced significantly.

[00863] The time history of the magnetic field can also be used to detect the type of flying object. Rocket propelled objects can have a thrust that is initially uniform. Accordingly, the charged particles will be moving in a uniform manner for a time after being propelled from the flying object. The detected magnetic field, therefore, will also have a detectable amount of uniformity over time when the range influence is taken into account. In contrast, hypersonic objects will lack this uniformity. For example, ions that leave a plasma field that surrounds the hypersonic object will not be ejected in a uniform manner. That is, the ions will travel in various different directions. The detected magnetic field based upon these ions will have a lot of variation that is not dependent on the range of the flying object. Accordingly, analysis of the intensity of the magnetic field, taking into account range influence, can determine if the magnetic field is uniform or has a large variation over time. Additional data can be used to refine this analysis. For example, calculating and determining a speed of an object can be used to eliminate possible flying objects that cannot fly at the determined speed. In addition, data from different types of detectors can be used. Radar data, acoustic data, etc., can be used in combination with detector data to eliminate possible types of flying objects.

[00864] Data combined from multiple sensors can also be used to more accurately calculate data associated with the flying object. For example, the time difference between when two separate detectors can be used to calculate a range of speeds and possible locations of the flying object. A first detector can first detect a flying object at a first time. A second detector can first detect the flying object at a second time. Using the known distance between the two detectors and the range of the two detectors, estimates of the speed and location of the flying object can be significantly enhanced compared to using data from a single detector. For example, the flying object is determined to be between two detectors rather than being on the opposite of the first detector. Further, the direction of the flying object can be deduced. The addition of a third detector allows for the location of the flying object to be triangulated.

[00865] DIAMOND NITROGEN VACANCY SENSED FERRO-FLUID HYDROPHONE

[00866] Figure 149 is a schematic illustrating a hydrophone 14900 in accordance with some illustrative implementations. In various implementations the components of the hydrophone 14900 can be contained within a housing 14902. The hydrophone 14900 includes a ferro-fluid 14904 that is exposed. In this implementation, the hydrophone can be exposed to air, water, a fluid, etc. A magnet 14908 activates the ferro-fluid 14904. In some implementations, the magnet 14908 is strong enough to keep the ferro-fluid 14904 in place in the hydrophone. In other implementations, a membrane can be used to contain the ferro-fluid 14904. When activated the ferro-fluid 14904 forms a shape based upon the magnetic field from the magnet 14908. The magnet 14908 can be a permanent magnet of an electro-magnet. As sound waves hit the ferro-fluid 14904, the shape of the ferro-fluid changes. As the ferro-fluid changes, the magnetic field from the ferro-fluid 14904 changes. One or more DNV sensors 14906 can be used to detect these changes in the magnetic field. The magnetic field changes measured by the DNV sensors 14906 can be converted into acoustic signals. For example, one or more electric processors can be used to translate movement of the ferro-fluid 14904 into acoustic data. The hydrophone 14900 can be used in medical devices as well as within vehicles.

[00867] A reservoir (not shown) can be used to hold additional ferro-fluid. As needed, the ferro-fluid 14904 that is being used to be detect sound waves can be replenished by the additional ferro-fluid from the reservoir. For example, a sensor can detect how much ferro-fluid is currently being used and control the reservoir to inject an amount of the additional ferro-fluid.

[00868] Figure 150 is a schematic illustrating a portion of a vehicle 15002 with a hydrophone in accordance with some illustrative implementations. The components of the hydrophone are similar to those described in Figure 149. A ferro-fluid 15004 is activated by a magnet 15008. In this implementation, the ferro-fluid 15004 is contained with a cavity 15010. The magnet 15008 is strong enough such that the ferro-fluid 15004 is contained within the cavity 15010 even when the vehicle is moving. As the cavity 15010 is not enclosed, the ferro-fluid 15004 is exposed to the fluid in which the vehicle is traveling. For example, if the vehicle is a submarine, the ferro-fluid 15004 is exposed to the water. In other implementations, the vehicle travels in the air and the ferro-fluid 15004 is exposed to air.

[00869] Prior to use, the ferro-fluid 15004 can be stored in a container 15012. The ferro-fluid 15004 can then be injected into the cavity 15010. In addition, during operation the amount of ferro-fluid 15004 contained within the cavity 15010 can be replenished with ferro-fluid from the container 15012.

[00870] As sound waves contact the ferro-fluid 15004, the ferro-fluid 15004 changes shape. The change in shape can be detected by one or more DNV sensors 15006. In one implementation, a single DNV sensor can be used. In other implementations an array of DNV sensors can be used. For example, multiple DNV sensors can be place in a ring around the cavity 15010. Readings from the DNV sensors 15006 can be translated into acoustic signals.

[00871] Figure 151 is a schematic illustrating a portion of a vehicle with a hydrophone with a containing membrane in accordance with some illustrative implementations. This implementation contains similar components as to implementation illustrated in Figure 150.

What is different is that a membrane 15114 covers a portion of or the entire opening of the cavity 15010. The membrane 15114 can help enclose and contain the ferro-fluid 15004 within the cavity 15010.

[00872] Figure 152 is a schematic illustrating a portion of a vehicle with a hydrophone in accordance with some illustrative implementations. In this implementation, a ferro-fluid 15204 is not contained within any cavity. Rather, the ferro-fluid 15204 is located outside of the vehicle. The magnet 15008 is used to contain the ferro-fluid 15204 in place. In one implementation, the magnet 15008 is located within the vehicle. In other implementations, the magnet 15008 is located outside of the vehicle. In yet another implementation, a portion of the magnet 15008 is located within the vehicle and a portion of the magnet 15008 is located outside of the vehicle.

[00873] Figure 153 is a schematic illustrating a portion of a vehicle with a hydrophone with a containing membrane in accordance with some illustrative implementations. Similar to Figure 152, the ferro-fluid 15204 is located outside of the vehicle. The ferro-fluid 15204 is enclosed within a membrane 15314 that contains the ferro-fluid 15204 near the vehicle. In this implementation, the magnet 15008 can be used to contain the ferro-fluid 15204, but the combination of the magnet 15008 and the membrane 15314 can be used to ensure that the ferro-fluid 15204 remains close enough to the vehicle to allow the DNV sensors to read the changes to the ferro-fluid 15204.

[00874] AC VECTOR MAGNETIC ANOMALY DETECTION WITH DIAMOND NITROGEN VACANCIES

[00875] FIG. 154 is a schematic of a system 15400 for AC magnetic vector anomaly detection, according to an embodiment of the invention. The system 15400 includes an optical excitation source 15410, which directs optical excitation to an NV diamond material 15420 with NV centers, or another magneto-optical defect center material with magneto-optical defect centers. An RF excitation source 15430 provides RF radiation to the NV diamond material 15420. A magnetic field generator 15470 generates a magnetic field, which is detected at the NV diamond material 15420.

[00876] The magnetic field generator 15470 may generate magnetic fields with orthogonal polarizations, for example. In this regard, the magnetic field generator 15470 may include two or more magnetic field generators, such as including a first magnetic field generator 15470a and a second magnetic field generator 15470b. Both the first and second magnetic field generators 15470a and 15470b may be Helmholtz coils, for example. The first magnetic field generator 15470a may be arranged to provide a magnetic field which has a first direction 15472a at the NV diamond material 15420. The second magnetic field generator 15470b may be arranged to provide a magnetic field which has a second direction 15472b at the NV diamond material 15420. Preferably, both the first magnetic field generator 15470a and the second magnetic field generator 15470b provide relatively uniform magnetic fields at the NV diamond material 15420. The second direction 15472b may be orthogonal to the first direction 15472a, for example. The system 15400 may be arranged such that an object 15415 is disposed between the magnetic field generator 15470 and theNV diamond material 15420.

[00877] The two or more magnetic field generators of the magnetic field generator 15470 may disposed at the same position, or may be separated from each other. In the case that the two or more magnetic field generators are separated from each other, the two or more magnetic field generators may be arranged in an array, such as a one-dimensional or two-dimensional array, for example.

[00878] The system 15400 may be arranged to include one or more optical detection systems 15405, where each of the optical detection systems 15405 includes the optical detector 15440, optical excitation source 15410 and NV diamond material 15420. Furthermore, the two or more magnetic field generators of the magnetic field generator 15470 may have a relatively high power as compared to the optical detection systems 15405. In this way, the optical systems 15405, may be deployed in an environment which requires a relatively lower power for the optical systems 15405, while the magnetic field generator 15470 may be deployed in an environment which has a relatively high power available for the magnetic field generator 15470 so as to apply a relatively strong magnetic field.

[00879] The system 15400 further includes a controller 15480 arranged to receive a light detection signal from the optical detector 15440 and to control the optical excitation source 15410, the RF excitation source 15430 and the magnetic field generator 15470. The controller may be a single controller, or multiple controllers. For a controller including multiple controllers, each of the controllers may perform different functions, such as controlling different components of the system 15400. The magnetic field generator 15470 may be controlled by the controller 15480 via an amplifier 15460, for example.

[00880] The RF excitation source 15430 may be a microwave coil, for example. The RF excitation source 15430 is controlled to emit RF radiation with a photon energy resonant with the transition energy between the ground ms = 0 spin state and the ms = ±1 spin states as discussed above with respect to FIG. 3.

[00881] The optical excitation source 15410 may be a laser or a light emitting diode, for example, which emits light in the green, for example. The optical excitation source 15410 induces fluorescence in the red from the NV diamond material 15420, where the fluorescence corresponds to an electronic transition from the excited state to the ground state. Light from the NV diamond material 15420 is directed through the optical filter 15450 to filter out light in the excitation band (in the green for example), and to pass light in the red fluorescence band, which in turn is detected by the optical detector 15440. The optical excitation light source 15410, in addition to exciting fluorescence in the NV diamond material 15420, also serves to reset the population of the ms = 0 spin state of the ground state 3 A2 to a maximum polarization, or other desired polarization.

[00882] The controller 15480 is arranged to receive a light detection signal from the optical detector 15440 and to control the optical excitation source 15410, the RF excitation source 15430 and the magnetic field generator 15470. The controller may include a processor 15482 and a memory 15484, in order to control the operation of the optical excitation source 15410, the RF excitation source 15430 and the magnetic field generator 15470. The memory 15484, which may include a nontransitory computer readable medium, may store instructions to allow the operation of the optical excitation source 15410, the RF excitation source 15430 and the magnetic field generator 15470 to be controlled. That is, the controller 15480 may be programmed to provide control.

[00883] ODMR detection of magnetic fields [00884] According to one embodiment of operation, the controller 15480 controls the operation of the optical excitation source 15410, the RF excitation source 15430 and the magnetic field generator 15470 to perform Optically Detected Magnetic Resonance (ODMR). The component of the magnetic field Bz along the NV axis of NV centers aligned along directions of four different orientation classes of the NV centers may be determined by ODMR, for example, by using an ODMR pulse sequence according to a Ramsey pulse scheme, as shown in FIG. 155. FIG. 155 illustrates the sequence of optical excitation pulses 15510 provided by the optical excitation source 15410, and the microwave (MW) pulses 15520 provided by the RF excitation source 15430. In between each optical pulse 15510, two MW pulses 15520, separated by a time τ, and at a given RF frequency are provided. For ease of understanding, three MW pulses 15520 with three different frequencies, MW1, MW2 and MW3, are shown in FIG. 155, although a larger number of RF frequencies may be employed. The three different frequencies, MW1, MW2 and MW3, respectively correspond to three different NV center orientations. This allows for the determination of the spatial orientation of the channels detected.

[00885] FIG. 156 illustrates the fluorescence signal of the diamond material 15420 detected as a function of RF frequency over the range from 2.9 to 3.0 GHz. FIG. 156 shows three dips in fluorescence, where the microwave frequencies corresponding to MW1, MW2 and MW3 are shown in the corresponding dips. The dips respectively correspond to the magnetic field components along the NV axis for three diamond lattice directions. FIG. 156 illustrates the dips in fluorescence only for RF frequencies above the zero magnetic field 2.87 GHz line (where there is no splitting of the ms = ±1 spin states), while in general there will also be three corresponding dips below the 2.87 GHz line. The three dips in fluorescence above the zero magnetic field 2.87 GHz line correspond to the ms = +1 spin state, while the three dips in fluorescence below the zero magnetic field 2.87 GHz line correspond to the ms = -1 spin state.

As discussed above, the difference in photon energies between the corresponding dips is given by 2gpBBz, where g is the g-factor, μΒ is the Bohr magneton, and Bz is the component of the external magnetic field along the NV axis, and thus Bz for each of three diamond lattice directions may be determined. While FIG. 156 illustrates the dips in fluorescence respectively corresponding to three diamond lattice directions, four diamond lattice directions may be used instead, for example. The magnetic field vector, including magnitude and direction, may then be determined based on Bz components along different lattice directions.

[00886] The system 15400 may transmit code packets from the magnetic field generator 15470 to the NV diamond material 15420 by modulating code by controlling the magnetic field generator 15470. The transmitted code packet may then be demodulated. Transmitted code packets may be transmitted along two or more channels, such as two channels where one channel is based on a magnetic field generated by the first magnetic field generator 15470a, and a second channel is based on a magnetic field generated by the second magnetic field generator 15470b. The magnetic fields generated by the first and second magnetic field generators 15470a and 15470b may be orthogonal to each other at the NV diamond material 15420 in the absence of any present material where the present material alters the magnetic field which is generated by the magnetic field generators 15470a and 15470b and detected by the NV diamond material 15420. It should be noted that the present material need not be between the magnetic field generators 15470a and 15470b and the NV diamond material 15420.

[00887] The code packets, which may include a binary sequence, are modulated by the processor 15480, which controls the magnetic field generator 15470 to generate a time varying magnetic field, and transmits the code packets to the NV diamond material 15420. Specifically, the processor 15480 modulates a different correlated code, such as gold codes, for each channel, where the correlated codes for the different channels are binary sequences which are optimized for a low cross correlation (between different correlation codes), and have a good autocorrelation. In the case of two channels, the processor 15480 may control the first magnetic field generator 15470a to transmit a first correlated code, and further control the second magnetic field generator 15470b to transmit a second correlated code. Thus, the correlated code packets are transmitted via two channels, one for the first correlated code via the first magnetic field generator 15470a, and the other for the second correlated code via the second magnetic field generator 15470b. The correlated codes may be modulated by continuous phase modulation, and may be modulated by MSK frequency modulation, for example.

[00888] The transmission of code packets using correlated codes may provide gain as compared to simple DC transmission. In particular, longer codes provide an increased gain, but require a longer time for transmission.

[00889] The modulated code packets transmitted by the magnetic field generator 15470 are then detected using ODMR techniques as described above, and demodulated. The processor 15480 demodulates the correlated code packets by using a matched filter. The matched filter correlates with the transmitted correlated codes for each channel, and for each magnetic field projection along a lattice direction. It should be noted that the modulation for the different channels may be performed simultaneously. Likewise, the demodulation for the different channels may be performed simultaneously. FIG. 157A illustrates a match-filtered first correlated code for the magnetic field component along three lattice directions corresponding to the magnetic field provided by the first magnetic field generator 15470a, while FIG. 157B illustrates a match-filtered second correlated code for the magnetic field component along three lattice directions corresponding to the magnetic field provided by the second magnetic field generator 15470b. The spike shown for each of the three diamond lattice directions corresponds to the projected magnetic field along a respective of the three lattice directions. The magnetic field vector, including both magnitude and direction, may then be reconstructed based on the projected magnetic fields along the three lattice directions.

[00890] If there is an object 15415 present which affects the magnetic field generated by the magnetic field generator 15470 where the magnetic field is felt by the NV diamond material 15420, the magnetic field vector detected at the NV diamond material 15420 will change. FIG. 158 illustrates the reconstructed magnetic field vector for two correlated codes for the case where an object 15415 is disposed between the magnetic field generator 15470 and the NV diamond material 15420, in the case where the first correlated code is transmitted via the first magnetic field generator 15470a, and the second correlated code is transmitted via the second magnetic field generator 15470b. FIG. 158 illustrates both the case where the object 15415 is a ferrous object and where no object 15415 is present.

[00891] For a ferrous object, however, the reconstructed magnetic field vector for first correlated code rotates about 46° relative to that for no object, while the second correlated code rotates about 28° relative to that for no object. That is, the ferrous object affects the magnetic field at the NV diamond material 15420 applied by first magnetic field generator 15470a more than the magnetic field at the NV diamond material 15420 applied by second magnetic field generator 15470b. This result provides two insights, first, the system 15400 may detect magnetic anomalies due to a ferrous object affecting the magnetic field felt by the NV diamond material 15420 which is generated by the magnetic field generator 15470 acting as a transmitter, and second, two different channels, providing orthogonal probing magnetic fields, may be applied simultaneously, thus providing an increase in the magnetic parameters probed. The reconstructed magnetic field vector, in addition to changing direction due to the presences of a ferrous object, may also change in magnitude. The AC nature of the ODMR technique employed reduces DC bias.

[00892] Frequency Based Detection [00893] The present system allows for frequency based detection based on frequency dependent attenuation in the magnetic field provided by the magnetic field generator 15470. While FIG. 158 illustrates magnetic anomaly detection of a ferrous object, a non-ferrous object may also be detected, such as an object formed of an electrically conductive material. For example, if the non-ferrous object provides for a frequency dependent attenuation in the magnetic field provided by the magnetic field generator 15470, the non-ferrous object may be detected.

[00894] While frequency based detection may allow for a greater range of objects detected, the frequency based detection may further allow for operation in a less noisy environment. In this case, the frequency range is set to a range with less noise.

[00895] Magnetic Anomaly Detection [00896] The system 15400 for AC magnetic vector anomaly detection may further include a reference library which may be stored in the memory 15484 of the controller 15480, or stored separately from the memory 15484. In either case, the reference library is accessible to the processor 15482. The reference library contains reference magnetic field vectors corresponding to different objects. The reference library contains a reference magnetic field vector both for the first correlation code, corresponding to the magnetic field generated by the first magnetic field generator 15470a, and the second correlation code, corresponding to the magnetic field generated by the second magnetic field generator 15470b.

[00897] The reference magnetic field vectors for the first correlation code and the second correlation code from the reference library may be compared to the reconstructed magnetic field vectors as determined by the system 15400. An object may be identified based on a match between the reference magnetic field vectors from the reference library and the reconstructed magnetic field vectors as determined by the system 15400. Using two or more correlation codes, corresponding to different, preferably orthogonal, polarizations of the magnetic field applied to the NV diamond material 15420, provides increased accuracy in identification of an object because a match for both polarizations is needed for identification.

[00898] As discussed above, providing improved magnetic anomaly detection may be accomplished by incorporating a magnetic field generator which generates two or more separate magnetic fields at the NV diamond material, or other magneto-optical material, where the magnetic fields may be orthogonal to each other. The magnetic fields may generated in two or more different channels, where the effect on the magnetic field due to a nearby magnetic object in the two different channels provides an increased number of magnetic parameters, which enhances the identification of the object.

[00899] Applying the magnetic field for the different channels can be accomplished by modulating the magnetic field applied and transmission of correlation code packets, followed by detection and demodulation of the code packets. The different correlation codes for the different channels are binary sequences which have a small cross correlation. The correlation code packets may be demodulated using matched filtering providing magnetic field components along different diamond lattice directions. A magnetic vector may then be reconstructed using the magnetic field components, providing a reconstructed magnetic field vector for the different channels. The reconstructed magnetic field vectors of each of the channels may be compared to reference magnetic field vectors corresponding to objects with different magnetic material profiles to identify the object.

[00900] DEFECT DETECTOR FOR CONDUCTIVE MATERIALS

[00901] Nitrogen-vacancy centers (NV centers) are defects in a diamond’s crystal structure, which can purposefully be manufactured in synthetic diamonds. In general, when excited by green light and microwave radiation, the NV centers cause the diamond to generate red light. When an excited NV center diamond is exposed to an external magnetic field the frequency of the microwave radiation at which the diamond generates red light and the intensity of the light change. By measuring the changes, the NV centers can be used to accurately detect the magnetic field strength.

[00902] In various embodiments described in greater detail below, a magnetometer using one or more diamonds with NV centers can be used to detect defects in conductive materials. According to Ampere’s law, an electrical current through a conductor generates a magnetic field along the length of the conductor. Similarly, a magnetic field can induce a current through a conductor. In general, a conductor with continuous uniformity in size, shape, and material through which an electrical current passes will generate a continuous magnetic field along the length of the conductor. On the other hand, the same conductor but with a deformity or defect such as a crack, a break, a misshapen portion, holes, pits, gouges, impurities, anomalies, etc. will not generate a continuous magnetic field along the length of the conductor. For example, the area surrounding the deformity may have a different magnetic field than areas surrounding portions of the conductor without the deformity. In some deformities, such as a break in the conductor, the magnetic field on one side of the break may be different than the magnetic field on the other side of the break.

[00903] For example, a rail of railroad tracks may be checked for deformities using a magnetometer. A current can be induced in the rail, and the current generates a magnetic field around the rail. The magnetometer can be used by passing the magnetometer along the length of the rail, or along a portion of the rail. The magnetometer can be at the same location with respect to the central axis of the rail as the magnetometer passes along the length of the rail. The magnetometer detects the magnetic field along the length of the rail.

[00904] In some embodiments, the detected magnetic field can be compared to an expected magnetic field. If the detected magnetic field is different than the expected magnetic field, it can be determined that a defect exits in the rail. In some embodiments, the detected magnetic field along the length of the rail can be checked for areas that have a magnetic field that is different than the majority of the rail. It can be determined that the area that has a magnetic field that is different than the majority of the rail is associated with a defect in the rail.

[00905] The principles explained above can be applied to many scenarios other than checking the rails of railroad tracks. A magnetometer can be used to detect deformities in any suitable conductive material. For example, a magnetometer can be used to detect deformities in machinery parts such as turbine blades, wheels, engine components.

[00906] Figs. 159A and 159B are block diagrams of a system for detecting deformities in a material in accordance with an illustrative embodiment. An illustrative system 15900 includes a conductor 15905, an alternating current (AC) source 15910, a coil 15915, and a magnetometer 15930. In alternative embodiments, additional, fewer, and/or different elements may be used.

[00907] The conductor 15905 is a length of conductive material. In some embodiments, the conductor 15905 is paramagnetic. In some embodiments, the conductor 15905 is ferromagnetic. The conductor 15905 can be any suitable length and have any suitable cross-sectional shape.

[00908] A current indicated by the arrow labeled 15920 in Figs. 159A and 159B illustrates the direction of an induced current through the conductor 15905. In the embodiments illustrated in Figs. 159A and 159B, the AC source 15910 and the coil 15915 induce the induced current 15920. For example, current from the AC source 15910 can pass through the coil 15915, thereby creating a magnetic field around the coil 15915. The magnetic field of the coil 15915 can be placed sufficiently close to the conductor 15905 to create the induced current 15920. The induced current 15920 travels in a direction along the conductor 15905 that is away from the coil 15915. In alternative embodiments, any suitable system can be used to create the induced current 15920.

[00909] In the embodiments illustrated in Figs. 159A and 159B, an AC source 15910 is used to provide power to the coil 15915. The AC source 15910 can be any suitable alternating current source. For example, power lines or traditional methods of obtaining alternating current power can be used. In another example, a third rail of a railway that is used to provide power to railcars can be used as the AC source 15910. In yet another example, a crossing gate trigger of a railway can be used as the AC source 15910.

[00910] In an illustrative embodiment, the induced current 15920 is an alternating current. In some embodiments, the frequency of the induced current 15920 can be altered. The magnetic field generated by the induced current 15920 can change based on the frequency of the induced current 15920. Thus, by using different frequencies, different features of the conductor 15920 can be determined by measuring the magnetic field generated by the different frequencies, as explained in greater detail below. For example, a rapid sequence of different frequencies can be used. In another example, multiple frequencies can be applied at once and the resulting magnetic field can be demodulated. For example, the spatial shape and pattern of the vector magnetic field generated by eddy currents around the defect or imperfection changes with the frequency of the applied excitation field. A three-dimensional Cartesian magnetic field pattern around the defect or imperfection can be measured and imaged at one frequency at a time. The detected magnetic field pattern can be stored (e.g., in a digital medium or a continuous analog medium). The detected magnetic field pattern can be compared to previously measured images to generate a likely taxonomy or identification of the nature of the defect or imperfection and/or the location of the defect or imperfection.

[00911] The induced current 15920 that passes through the conductor 15905 generates a magnetic field. The magnetic field has a direction around the conductor 15905 indicated by the arrow labeled with numeral 15925. The magnetometer 15930 can be passed along the length of the conductor 15905. Figs. 159A and 159B include an arrow parallel to the length of the conductor 15905 indicating the path of the magnetometer 15930. In alternative embodiments, any suitable path may be used. For example, in embodiments in which the conductor 15905 is curved (e.g., as a railroad rail around a corner), the magnetometer 15930 can follow the curvature of the conductor 15905.

[00912] The magnetometer 15930 can measure the magnitude and/or direction of magnetic field vectors along the length of the conductor 15905. For example, the magnetometer 15930 measures the magnitude and the direction of the magnetic field at multiple sample points along the length of the conductor 15905 at the same orientation to the conductor 15905 at the sample points. For instance, the magnetometer 15930 can pass along the length of the conductor 15905 while above the conductor 15905.

[00913] Any suitable magnetometer can be used as the magnetometer 15930. In some embodiments, the magnetometer uses one or more diamonds with NV centers. The magnetometer 15930 can have a sensitivity suitable for detecting changes in the magnetic field around the conductor 15905 caused by deformities. In some instances, a relatively insensitive magnetometer 15930 may be used. In such instances, the magnetic field surrounding the conductor 15905 should be relatively strong. In some such instances, the current required to pass through the conductor 15905 to create a relatively strong magnetic field may be impractical or dangerous. Thus, for example, the magnetometer 15930 can have a sensitivity of about 10'9 Tesla (one nano-Tesla) and can detect defects at a distance of about one to ten meters away from the conductor 15905. In such an example, the conductor 15905 can be a steel pipe with a diameter of 0.2 meters. In one example, the current through the conductor 15905 may be about one Ampere (Amp), and the magnetometer 15930 may be about one meter away from the conductor 15905. In another example, the current through the conductor 15905 may be about one hundred Amps, and the magnetometer 15930 may be about ten meters away. The magnetometer 15930 can have any suitable measurement rate. In an illustrative embodiment, the magnetometer 15930 can measure the magnitude and/or the direction of a magnetic field at a particular point in space up to one million times per second. For example, the magnetometer 15930 can take one hundred, one thousand, ten thousand, or fifty thousand times per second.

[00914] In embodiments in which the magnetometer 15930 measures the direction of the magnetic field, the orientation of the magnetometer 15930 to the conductor 15905 can be maintained along the length of the conductor 15905. As the magnetometer 15930 passes along the length of the conductor 15905, the direction of the magnetic field can be monitored. If the direction of the magnetic field changes or is different than an expected value, it can be determined that a deformity exits in the conductor 15905.

[00915] In such embodiments, the magnetometer 15930 can be maintained at the same orientation to the conductor 15905 because even if the magnetic field around the conductor 15905 is uniform along the length of the conductor 15905, the direction of the magnetic field is different at different points around the conductor 15905. For example, referring to the induced current magnetic field direction 15925 of Fig. 159A, the direction of the magnetic field above the conductor 15905 is pointing to the right-hand side of the figure (e.g., according to the “right-hand rule”). The direction of the magnetic field below the conductor 15905 is pointing to the left-hand side of the figure. Similarly, the direction of the magnetic field is down at a point that is to the right of the conductor 15905. Following the same principle, the direction of the magnetic field is up at a point that is to the left of the conductor 15905. Therefore, if the induced current 15920 is maintained at the same orientation to the conductor 15905 along the length of the conductor 15905 (e.g., above the conductor 15905, below the conductor 15905, twelve degrees to the right of being above the conductor 15905, etc.), the direction of the magnetic field can be expected to be the same or substantially similar along the length of the conductor 15905. In some embodiments, the characteristics of the induced current 15920 can be known (e.g.,

Amps, frequency, etc.) and the magnitude and direction of the magnetic field around the conductor 15905 can be calculated.

[00916] In embodiments in which the magnetometer 15930 measures magnitude of the magnetic field and not the direction of the magnetic field, the magnetometer 15930 can be located at any suitable location around the conductor 15905 along the length of the conductor 15905, and the magnetometer 15930 may not be held at the same orientation along the length of the conductor 15905. In such embodiments, the magnetometer 15930 may be maintained at the same distance from the conductor 15905 along the length of the conductor 15905 (e.g., assuming the same material such as air is between the magnetometer 15930 and the conductor 15905 along the length of the conductor 15905).

[00917] Fig. 159A illustrates the system 15900 in which the conductor 15905 does not contain a deformity. Fig. 159B illustrate the system 15900 in which the conductor 15905 includes a break 15935. As shown in Fig. 159B, a portion of the induced current 15920 is reflected back from the break 15935 as shown by the reflected current 15940. As in Fig. 159B, the induced current magnetic field direction 15925 corresponds to the induced current 15920. The reflected current magnetic field direction 15945 corresponds to the reflected current 15940. The induced current magnetic field direction 15925 is opposite the reflected current magnetic field direction 15945 because the induced current 15920 travels in the opposite direction from the reflected current 15940.

[00918] In some embodiments in which the break 15935 is a full break that breaks conductivity between the portions of the conductor 15905, the magnitude of the induced current 15920 may be equal to or substantially similar to the reflected current 15940. Thus, the combined magnetic field around the conductor 15905 will be zero or substantially zero. That is, the magnetic field generated by the induced current 15920 is canceled out by the equal but opposite magnetic field generated by the reflected current 15940. In such embodiments, the break 15935 may be detected using the magnetometer 15930 by comparing the measured magnetic field, which is substantially zero, to an expected magnetic field, which is a non-zero amount. As the magnetometer 15930 travels closer to the break 15935, the magnitude of the detected magnetic field reduces. In some embodiments, it can be determined that the break 15935 exists when the measured magnetic field is below a threshold value. In some embodiments, the threshold value may be a percentage of the expected value, such as ±0.1%, ±1%, ±5%, ±10%, ±15%, ±50%, or any other suitable portion of the expected value. In alternative embodiments, any suitable threshold value may be used.

[00919] In embodiments in which the break 15935 allows some of the induced current 15920 to pass through or around the break 15935, the magnitude of the reflected current 15940 is less than the magnitude of the induced current 15920. Accordingly, the magnitude of the magnetic field generated by the reflected current 15940 is less than the magnitude of the magnetic field generated by the induced current 15920. Although the magnitudes of the induced current 15920 and the reflected current 15940 may not be equal, the induced current magnetic field direction 15925 and the reflected current magnetic field direction 15945 are still opposite. Thus, the net magnetic field is a magnetic field in the induced current magnetic field direction 15925. The magnitude of the net magnetic field is the magnitude of the magnetic field generated by the induced current 120 minus the magnitude of the magnetic field generated by the reflected current 15940. As mentioned above, the magnetic field measured by the magnetometer 15930 can be compared against a threshold value. Depending upon the severity, size, and/or shape of the break 15935, the net magnetic field sensed by the magnetometer 15930 may or may not be less than or greater than the threshold value. Thus, the threshold value can be adjusted to adjust the sensitivity of the system. That is, the more that the threshold value deviates from the expected value, the more severe the deformity in the conductor 15905 is to cause the magnitude of the sensed magnetic field to be less than the threshold value. Thus, the smaller the threshold value is, the finer, smaller, less severe, etc. deformities are that are detected by the system 15900.

[00920] As mentioned above, the direction of the magnetic field around the conductor 15905 can be used to sense a deformity in the conductor 15905. Fig. 160 illustrates current paths through a conductor with a deformity in accordance with an illustrative embodiment. Fig. 160 is meant to be illustrative and explanatory only and not meant to be limiting with respect to the functioning of the system.

[00921] A current can be passed through the conductor 16005, as discussed above with regard to the conductor 15905. The current paths 16020 illustrate the direction of the current. As shown in Fig. 160, the conductor 16005 includes a deformity 16035. The deformity 16035 can be any suitable deformity, such as a crack, a dent, an impurity, etc. The current passing through the conductor 16005 spreads uniformly around the conductor 16005 in portions that do not include the deformity 16035. In some instances, the current may be more concentrated at the surface of the conductor 16005 than at the center of the conductor 16005.

[00922] In some embodiments, the deformity 16035 is a portion of the conductor 16005 that does not allow or resists the flow of electrical current. Thus, the current passing through the conductor 16005 flows around the deformity 16035. As shown in Fig. 159A, the induced current magnetic field direction 15925 is perpendicular to the direction of the induced current 15920. Thus, as in Fig. 159A, when the conductor 15905 does not include a deformity, the direction of the magnetic field around the conductor 15905 is perpendicular to the length of the conductor 15905 all along the length of the conductor 15905.

[00923] As shown in Fig. 160, when the conductor 16005 includes a deformity 16035 around which the current flows, the direction of the current changes, as shown by the current paths 16020. Thus, even though the conductor 16005 is straight, the current flowing around the deformity 16035 is not parallel to the length of the conductor 16005. Accordingly, the magnetic field generated by the current paths corresponding to the curved current paths 16020 is not perpendicular to the length of the conductor 16005. Thus, as a magnetometer such as the magnetometer 15930 passes along the length of the conductor 16005, a change in direction of the magnetic field around the conductor 16005 can indicate that the deformity 16035 exits. As the magnetometer 15930 approaches the deformity 16035, the direction of the magnetic field around the conductor 16005 changes from being perpendicular to the length of the conductor 16005. As the magnetometer 15930 passes along the deformity 16035, the change in direction of the magnetic field peaks and then decreases as the magnetometer 15930 moves away from the deformity 16035. The change in the direction of the magnetic field can indicate the location of the deformity 16035. In some instances, the conductor may have a deformity that reflects a portion of the current, as illustrated in Fig. 159B, and that deflects the flow of the current, as illustrated in Fig. 160.

[00924] The size, shape, type, etc. of the deformity 16035 determines the spatial direction of the magnetic field surrounding the deformity 16035. In some embodiments, multiple samples of the magnetic field around the deformity 16035 can be taken to create a map of the magnetic field. In an illustrative embodiment, each of the samples includes a magnitude and direction of the magnetic field. Based on the spatial shape of the magnetic field surrounding the deformity 16035, one or more characteristics of the deformity 16035 can be determined, such as the size, shape, type, etc. of the deformity 16035. For instance, depending upon the map of the magnetic field, it can be determined whether the deformity 16035 is a dent, a crack, an impurity in the conductor, etc. In some embodiments, the map of the magnetic field surrounding the deformity 16035 can be compared to a database of known deformities. In an illustrative embodiment, it can be determined that the deformity 16035 is similar to or the same as the closest matching deformity from the database. In an alternative embodiment, it can be determined that the deformity 16035 is similar to or the same as a deformity from the database that has a similarity score that is above a threshold score. The similarity score can be any suitable score that measures the similarity between the measured magnetic field and one or more known magnetic fields of the database.

[00925] A magnetometer can be used to detect defects in conductive materials in many different situations. In one example, a magnetometer can be used to detect defects in railroad rails. In such an example, a railroad car can be located along the rails and travel along the tracks. A magnetometer can be located on the car a suitable distance from the rails, and monitor the magnetic field around one or more of the rails as the car travels along the tracks. In such an example, the current can be induced in one or more of the rails at a known stationary location. In an alternative embodiment, the coil that induces the current in the rails can be located on the moving car and can move with the magnetometer.

[00926] In such an example, the magnetometer can be located on a typical rail car or a specialized rail car device. The magnetometer can be mounted and/or the rail car can be designed in a manner that maintains the orientation of the magnetometer with respect to one or more of the rails. In some instances, it may not be feasible to maintain perfect orientation of the magnetometer with the rails because of, for example, bumps or dips in the terrain, movement of people or cargo in the car, imperfections in the rails, etc. In such instances, one or more gyroscopes can be used to track the relative position of the magnetometer to the one or more rails. In alternative embodiments, any suitable system can be used to track the relative position of the magnetometer, such as sonar, lasers, or accelerometers. The system may use the change in relative position to adjust the magnitude and/or direction of the expected magnetic field accordingly.

[00927] In another example, the magnetometer can be used to detect deformities in pipes. In some instances, the pipes can be buried or may be beneath water. In scenarios in which the conductor being checked for deformities is surrounded by a relatively conductive material, such as water, the magnetometer can be placed relatively close to the coil inducing the current in the conductor. Because the conductor is surrounded by the relatively conductive material, the strength of the current traveling through the conductor will diminish much quicker the further away from the coil the magnetometer is compared to the conductor being surrounded by a relatively non-conductive material, such as air. In such conditions, the coil can travel along the conductor with the magnetometer. The magnetometer and the coil can be separated enough that the magnetic field from the coil does not cause excessive interference with the magnetometer.

[00928] In some instances, a magnetometer can be used to detect leaks in pipes. For example, some fluids that are transported via a pipeline have magnetic properties. In such instances, the fluid and/or the pipe can be magnetized. The magnetometer (e.g., an array of magnetometers) can travel along the pipe to detect discrepancies in the detected magnetic field around the pipe as explained above. Differences or changes in the magnetic field can be caused by the fluid leaking from the pipe. Thus, detecting a difference or change in the magnetic field using the magnetometer can indicate a leak in the pipe. For example, a stream or jet of fluid or gas flowing from a pipe can be detected by a magnetic field around the stream or jet. In some embodiments, the volumetric leak rate can be determined based on the magnetic field (e.g., the size of the magnetic field). The leak rate can be used, for example, to prioritize remediation of leaks.

[00929] In some embodiments, a current may not be induced in the conductor. In such embodiments, any suitable magnetic field may be detected by the magnetometer. For example, the earth generates a magnetic field. The material being inspected may deflect or otherwise affect the earth’s magnetic field. If the inspected material is continuous, the deflection of the earth’s magnetic field is the same or similar along the length of the material. However, if there is a deformity or defect, the deflection of the earth’s magnetic field will be different around the deformity or defect.

[00930] In some embodiments, any other suitable magnetic source may be used. For example, a source magnet may be applied to a material that is paramagnetic. The magnetic field around the paramagnetic material can be used to detect deformities in the material using principles explained herein. In such an embodiment, the magnetometer can be located relatively close to the source magnet.

[00931] As mentioned above, in some embodiments the measured magnetic field is compared to an expected magnetic field. The expected magnetic field can be determined in any suitable manner. The following description is one example of how the expected magnetic field can be determined.

[00932] In embodiments in which a coil is used to induce a current in the conductor (e.g., the embodiments illustrated in Figs. 159A and 159B), the magnitude of the magnetic field of the coil at the conductor, BC0l\ can be determined using equation (cl):

In equation (cl), μ is the magnetic permeability (Newtons/Amp2) of the medium between the coil and the conductor (e.g., conductor 15905), / is the current through the coil (Amps), dlcon is the elemental length of the coil wire (meters), and rcr is the scalar distance from the coil to the rail (meters). It will be understood that he magnitude of the magnetic field of the coil of equation (cl) can be converted into a vector quantity with a circular profile symmetric about the coil center of alignment and, therefore, circumferentially constant with a radial relationship consistent with equation (cl).

[00933] The forward current in the rail, Fad, can be calculated using equation (c2): (c2) Irail = a Bcoil

In equation (c2), a is the magnetic susceptibility of the conductor (Henry).

[00934] The magnitude of the magnetic field of the rail magnetic B-field is:

In equation (c3), rnn is the distance from the rail to the magnetometer, and dlraii is the length of the rail from the location the magnetic field from the coil interacts with the rail and the location of the magnetometer (meters).

[00935] In some embodiments, the magnetometer can measure the magnitude of a magnetic field in one or more directions. For example, the magnetometer can measure the magnitude of the magnetic field in three orthogonal directions: x, y, and z. Equation (c4) shows the relationship between the measured magnitudes of the detected magnetic field in the x, y, and z directions (Bx, By, and //-, respectively) and the vector of the magnetic field measured by the magnetometer (Bmeas) (e.g., using a dipole model):

If the rail is uniform and homogeneous, then Bmeas is essentially equal to When a defect, anomaly, deformity, etc. is present within the rail, the measured magnetic vector, Bmeas, is different from the expected magnetic field of the rail, Brml, by a function of translation (Ft ) because of the anomaly, as shown in equation (c5): (c5) Bmeas = Ft Brail [00936] A linear expansion of the translation function allows an algebraic formula isolating position, δ, changes caused by the rail anomaly to be detected from a difference between the reference and measured field as follows:

In equations (c6)-(c9), □ is the distance of the deformity along the conductor from the magnetometer, Iraii is the current through the conductor, and k denotes a particular measurement sample. In an illustrative embodiment, one hundred samples are taken. In alternative embodiments, more or fewer than one hundred samples are taken. When processed through a Fast Fourier Transform algorithm (or any other suitable algorithm), noise may be suppressed and echoes or uneven departures from the reference field (Brad) are correlated to the rail break at a known position and orientation relative to the magnetometer at distance □ according to the following equations:

Using the equations above, the distance from the magnetometer to the deformation can be determined based on the current induced in the conductor (7) and the measured magnetic field at a particular distance from the conductor.

[00937] In the embodiments illustrated in Figs. 159A and 159B, one magnetometer 15930 is used to pass along the length of the conductor 15905 to monitor for deformities. In alternative embodiments, two or more magnetometers 15930 may be used. The multiple magnetometers 15930 can be oriented around the conductor 15905 in any suitable manner. Using multiple magnetometers 15930 provides benefits in some instances. For example, using multiple magnetometers 15930 provides multiple sample points simultaneously around the conductor 15905. In some instances, the multiple sample points can be redundant and can be used to check the accuracy of the samples. In some instances, having multiple sample points spread around a conductor 15905 increases the chances that there is a magnetometer 15930 at a point around the conductor 15905 that has the greatest angle of departure. That is, sampling multiple points around the conductor 15905 increases the chances that a magnetometer 15930 will detect an anomaly in the conductor 15905 based on the greatest change in the magnetic field around the conductor 15905.

[00938] Fig. 161 is a flow diagram of a method for detecting deformities in accordance with an illustrative embodiment. In alternative embodiments, additional, fewer, or different operations may be performed. Also, the use of a flow chart and/or arrows is not meant to be limiting with respect to the order or flow of operations. For example, in some embodiments, two or more of the operations may be performed simultaneously.

[00939] In an operation 16105, an expected magnetic field is determined. In an illustrative embodiment, the expected magnetic field can include a magnitude and a direction (e.g., be a vector). In alternative embodiments, the expected magnetic field includes a magnitude or a direction. In an illustrative embodiment, the expected magnetic field is determined based on a current induced in a conductor. For example, a power source and a coil can be used to induce a current in a conductor. Based on the current through the coil and the distance between the coil and the conductor (and any other suitable variable), the induced current through the conductor can be calculated. The location of the coil with respect to the magnetometer can be known, and, therefore, the direction of the induced current can be known. If the current through the conductor is known or calculated, the magnetic field at a point around the conductor can be calculated. Thus, the magnetic field at the point around the conductor that the magnetometer is can be calculated based on the induced current, assuming that no deformity exits.

[00940] In an alternative embodiment, the expected magnetic field can be determined using a magnetometer. As discussed above, a deformity can be detected by detecting a change in a magnetic field around a conductor. In such embodiments, one or more initial measurements can be taken using the magnetometer. The one or more initial measurements can be used as the expected magnetic field. That is, if the conductor is not deformed along the length of the conductor, the magnetic field along the conductor will be the same as or substantially similar to the initial measurements. In alternative embodiments, any suitable method for determining an expected magnetic field can be used.

[00941] In an operation 16110, a magnetic field is sensed. In an illustrative embodiment, a magnetometer is used to measure a magnetic field around a conductor along the length of the conductor. In an operation 16115, the magnetometer moves along the length of the conductive material. The magnetometer can maintain an orientation to the conductor as the magnetometer travels along the length of the conductor. As the magnetometer moves along the length of the conductive material, the magnetometer can be used to gather multiple samples along the length of the conductive material.

[00942] In an operation 16120, the difference between the sensed field and the expected field is compared to a threshold. In an illustrative embodiment, the absolute value of the difference between the sensed field and the expected field is compared to the threshold. In such an embodiment, the magnitude of the difference is used and not the sign of the value (e.g., negative values are treated as positive values). The threshold can be any suitable threshold value. For example, the difference between the magnitude of the sensed vector and the magnitude of the expected vector can be compared against a threshold magnitude value. In another example, the difference between the direction of the sensed vector and the direction of the expected vector can be compared against a threshold value. The threshold value can be chosen based on a desired level of sensitivity. The higher the threshold value is, the lower the sensitivity of the system is. For example, the threshold value for a difference in vector angles can be 5-10 micro radians. In alternative embodiments, the threshold value can be less than 5 micro radians or greater than 10 micro radians.

[00943] If the difference between the sensed field and the expected field is greater than the threshold, then it can be determined in an operation 16135 that there is a defect. In alternative embodiments, a sufficiently large difference in the sensed field and the expected field can indicate an anomaly in the conductor, a deformity in the conductor, etc. If the difference between the sensed field and the expected field is not greater than the threshold, then it can be determined in an operation 16140 that there is no defect. That is, if the sensed field is sufficiently close to the expected field, it can be determined that there is not a sufficiently large anomaly, break, deformity, etc. in the conductor.

[00944] IN-SITU POWER CHARGING

[00945] Widespread power line infrastructures, such as shown in Fig. 46, connect cities, critical power system elements, homes, and businesses. The infrastructure may include overhead and buried power distribution lines, transmission lines, third rail power lines, and underwater cables. In various embodiments described herein, one or more of the various power lines can be used to charge the power systems of the vehicular system 16200. In alternative embodiments, any suitable source of electromagnetic fields can be used to power the systems of the vehicular system 16200. For example, transmission towers such as cellular phone transmission towers can be used to power the systems of the vehicular system 16200.

[00946] In some embodiments, a conductor with a direct current (DC) may be used. By moving a magnetic field with respect to a coil, a current can be induced in the coil. If the magnetic field does not move with respect to the coil, a current is not induced. Thus, if a conductor has an AC current passing through the conductor, the magnetic field around the conductor is time-varying. In such an example, the coil can be stationary with respect to the coil and have a current induced in the conductor. However, if a DC current is passed through the conductor, a static magnetic field is generated about the conductor. Thus, if a coil does not move with respect to the conductor, a current is not induced in the coil. In such instances, if the coil moves with respect to the conductor, a current will be induced in the coil. Thus, in embodiments in which the power lines have DC power, the vehicle and/or the coil can move with respect to the power line. For example, the vehicle can travel along the length of the power line. In another example, the vehicle can oscillate positions, thereby moving the coil within the magnetic field.

[00947] In embodiments in which the vehicular system 16200 is an aerial vehicle, the power lines can be overhead lines. In such embodiments, the vehicular system 16200 can fly close enough to the overhead lines to induce sufficient current in the charging device to charge the power systems. In some embodiments, the power lines can be underground power lines. In such embodiments, the aerial vehicular system 16200 can fly close to the ground. In such embodiments, the electromagnetic field can be sufficiently strong to pass through the earth and provide sufficient power to the vehicular system 16200. In an alternative embodiment, the vehicular system 16200 can land above or next to the buried power lines to charge the power source. In embodiments in which the vehicular system 16200 is a land-based vehicle, the operation 16305 can include locating a buried power line.

[00948] In an operation 16310, the vehicular system 16200 can travel to the power line. For example, after identifying and/or locating the power line, the vehicular system 16200 can use suitable navigation systems and propulsion devices to cause the vehicular system 16200 to move sufficiently close to the power line.

[00949] In an operation 16315, the charging system is oriented with the power line. In an illustrative embodiment, the charging system includes one or more coils. Fig. 50 is an illustration of a vehicle in accordance with an illustrative embodiment. An illustrative unmanned aircraft system (UAS) 5000 includes a fuselage 5005 and wings 5010. In alternative embodiments, additional, fewer, and/or different elements may be used. In an illustrative embodiment, the fuselage 5005 includes a battery system. The fuselage 5005 may house other components such as a computing system, electronics, sensors, cargo, etc.

[00950] In an illustrative embodiment, one or more coils of the charging system can be located in the wings 5010. For example, each of the wings 5010 can include a coil. The coil can be located in the wings 5010 in any suitable manner. For example, the coil is located within a void within the wings 5010. In another example, the coil is bonded, fused, laminated, or otherwise attached to the wings 5010. In such an example, the coil can be formed within the material that makes up the wings 5010 or the coil can be attached to an outside or inside surface of the wings 5010. In alternative embodiments, the one or more coils can be located at any suitable location. The UAS 5000 is meant to be illustrative only. In alternative embodiments, any suitable vehicle can be used and may not be a fixed wing aircraft.

[00951] Any suitable coil of a conductor can be used to induce a current that can be used to charge batteries. In an illustrative embodiment, the coil is an inductive device. For example, the coil can include a conductor coiled about a central axis. In alternative embodiments, any suitable coil can be used. For example, the coil can be wound in a spherical shape. In alternative embodiments, the charging device can include dipoles, patch antennas, etc. In an illustrative embodiment, the operation 16315 includes orienting the coil to maximize the current induced in the coil. For example, the operation 16315 can include orienting the coil such that the direction of the magnetic field at the coil is parallel to the central axis of the coil. In such an example, a magnetometer can be used to determine the direction of the magnetic field at the coil. For example, each of the wings 5010 of the UAS 5000 include a coil and a magnetometer. In an embodiment in which the vehicle is a rotary-type vehicle (e.g., a helicopter style or quad-copter style vehicle), the vehicle can orient itself in a stationary position around the power lines to orient the direction of the magnetic field with the central axis of the coil.

[00952] In an illustrative embodiment, the operation 16315 includes navigating the vehicle to get the coil as close to the power line as possible. Fig. 164 is a graph of the strength of a magnetic field versus distance from the conductor in accordance with an illustrative embodiment. Line 16405 shows the strength of the magnetic field of a 1000 Ampere conductor, and line 16410 shows the strength of the magnetic field of a 100 Ampere conductor. As shown in Fig. 164, the magnitude of the magnetic field decreases at a rate proportional to the inverse of the distance from the source of the magnetic field. Thus,

where B is the magnitude of the magnetic field, and r is the distance from magnetic field source. For example, r is the distance from the power line. Thus, the closer the coil is to the power line, the more power can be induced in the coil to charge the batteries.

[00953] However, in some embodiments, practical limitations may dictate that a minimum distance be maintained between the vehicle and the power line. For example, damage can occur to the vehicle if the vehicle strikes or grazes the power line. In such an example, the vehicle may lose control or crash. In another example, the power line has high voltage and/or high current. For example, the voltage between power lines can be between five thousand to seven thousand volts and the power lines can carry about one hundred Amperes (Amps). In alternative embodiments, the power lines can have voltages above seven thousand volts or less than five thousand volts. Similarly, the power lines can have less than one hundred Amps or greater than one hundred Amps. In such an example, if the vehicle is close enough to the power lines, a static discharge may occur. Such a discharge may be a plasma discharge that can damage the vehicle.

[00954] In an illustrative embodiment, the vehicle is about one meter away from the power line. For example, one or more of the coils can be located one meter away from the power line. In alternative embodiments, the vehicle can be between one and ten meters away from the power line. In yet other embodiments, the vehicle can be between ten and twenty meters away from the power lines. In alternative embodiments, the vehicle is closer than one meter or further away than twenty meters from the power lines.

[00955] In an operation 16320, the power source can be charged. For example, the power source may include one or more batteries. Current induced in the coil can be used to charge the batteries. In an illustrative embodiment, the power in the power lines can be alternating current (AC) power. In such an embodiment, the magnetic field produced by the AC power alternates, and the current induced in the coil alternates. The vehicle can include a rectifier that converts the induced current to a direct current to charge one or more of the batteries.

[00956] In an operation 16325, the orientation of the charging system with the power line can be maintained. For example, the vehicle can maximize the amount of current induced in the coil while maintaining a suitable (e.g., safe) distance from the power line.

[00957] In embodiments in which the vehicle can charge while in a stationary position (e.g., a land vehicle or a rotary vehicle), the vehicle can maintain a consistent position near the power line. In embodiments in which the vehicle moves along the power line (e.g., when the vehicle is charging while traveling or if the vehicle is a fixed wing vehicle), the vehicle can follow the path of the power lines. For example, overhead power lines may sag between support poles. In such an example, the vehicle can follow the sagging (e.g., the catenary shape) of the power lines as the vehicle travels along the length of the power lines. For example, the vehicle can maintain a constant distance from the power line.

[00958] The vehicle can maintain a distance from the power lines in any suitable manner. For example, the UAS 5000 can include a magnetometer in each of the wings 5010. The UAS 5000 can triangulate the position of the power lines using the magnetometers. For example, the direction of the magnetic field around the power lines is perpendicular to the length of the power lines (e.g., perpendicular to the direction of current travel). Thus, based on the measured direction of the magnetic field, the direction of the power line can be determined. To determine the distance from the power line, the magnitude of the magnetic field measured at each of the magnetometers can be used to triangulate the distance to the power line. In alternative embodiments, any other suitable device may be used to determine the distance from the vehicle to the power lines. For example, the vehicle can use lasers, cameras, ultrasonic sensors, focal plane arrays, or infrared sensors to detect the location of the power lines.

[00959] RAPID HIGH-RESOLUTION MAGNETIC FIELD MEASUREMENTS FOR POWER LINE INSPECTION

[00960] In some aspects of the present technology, methods and configurations are disclosed for diamond nitrogen-vacancy (DNV) application to detection of defects in power transmission or distribution lines. A characteristic magnetic signature of power infrastructure may be used for inspection of the infrastructure. For example, power lines without defects have characteristic magnetic signatures. The magnetic signature of a power line can be measured and compared to the expected magnetic signature. Measured differences can indicate that there is a defect in the transmission line.

[00961] In some implementations, a magnetic sensor may be used to measure the magnetic signature of a transmission line. For example, the magnetic sensor can be equipped on a manned vehicle. The manned vehicle can move along the transmission line to measure the magnetic signature of the transmission line. In other implementations, the magnetic sensor can be included in an unmanned vehicle. The transmission line can then also be used to navigate the unmanned vehicle, allowing for unmanned inspection of the transmission line. An unmanned vehicle can maneuver using power lines and can also inspect the same power lines for defects.

[00962] Because the magnetic fields are being measured, the measurements of these magnetic fields are not hindered by vegetation or poor visibility conditions that impact other inspection methods such as a visual, optical, and laser inspection methods. Accordingly, the detection of defects such as a downed power line can proceed in poor visibility weather or when vegetation has overgrown the power lines.

[00963] In some implementations, the subject technology can include one or more magnetic sensors, a magnetic navigation database, and a feedback loop that can control an unmanned vehicle’s position and orientation. High sensitivity to magnetic fields of DNV magnetic sensors for magnetic field measurements can be utilized. The DNV magnetic sensor can also be low cost, space, weight, and power (C-SWAP) and benefit from a fast settling time. The DNV magnetic field measurements allow UAS systems to align themselves with the power lines, and to rapidly move along the power-line infrastructure routes. Navigation is enabled in poor visibility conditions and/or in GPS-denied environments. Further, the UAS operation may occur in close proximity to power lines facilitating stealthy transit. DNV-based magnetic sensors can be approximately 100 times smaller than conventional magnetic sensors and can have a reaction time that that is approximately 100,000 times faster than sensors with similar sensitivity.

[00964] FIGURE 44 is a conceptual diagram illustrating an example of an UAS 4402 navigation along power lines 4404, 4406, and 4408, according to some implementations of the subject technology. The UAS 4402 can exploit the distinct magnetic signatures of power lines for navigation such that the power lines can serve as roads and highways for the UAS 4402 without the need for detailed a priori knowledge of the route magnetic characteristics. As shown in FIGURE 45 A, a ratio of signal strength of two magnetic sensors, A and B (4410 and 4412 in Figure 44), attached to wings of the UAS 4402, varies as a function of distance, x, from a center line of an example three-line power transmission line structure 4404, 4406, and 4408. When the ratio is near 1, point 4522, the UAS 4402 is centered over the power transmission line structure, x=0 at point 4520.

[00965] A composite magnetic field (B-field) 4506 from all (3) wires shown in Figure 2B. This field is an illustration of the strength of the magnetic field measured by one or more magnetic sensors in the UAS. In this example, the peak of the field 208 corresponds to the UAS 4402 being above the location of the middle line 4406. When the UAS 4402 has two magnetic sensors, the sensors would read strengths corresponding to points 4502 and 4504. A computing system on the UAS or remote from the UAS, can calculate combined readings. Not all of the depicted components may be required, however, and one or more implementations may include additional components not shown in the figure. Variations in the arrangement and type of the components may be made, and additional components, different components, or fewer components may be provided.

[00966] As an example of various implementations, a vehicle, such as a UAS, can include one or more navigation sensors, such as DNV sensors. The vehicle’s goal could be to travel to an initial destination and possibly return to a final destination. Known navigation systems can be used to navigate the vehicle to an intermediate location. For example, a UAS can fly using GPS and/or human controlled navigation to the intermediate location. The UAS can then begin looking for the magnetic signature of a power source, such as power lines. To find a power line, the UAS can continually take measurements using the DNV sensors. The UAS can fly in a circle, straight line, curved pattern, etc. and monitor the recorded magnetic field. The magnetic field can be compared to known characteristics of power lines to identify if a power line is in the vicinity of the UAS. For example, the measured magnetic field can be compared with known magnetic field characteristics of power lines to identify the power line that is generating the measured magnetic field. In addition, information regarding the electrical infrastructure can be used in combination with the measured magnetic field to identify the current source. For example, a database regarding magnetic measurements from the area that were previously taken and recorded can be used to compare the current readings to help determine the UAS’s location.

[00967] In various implementations, once the UAS identifies a power line the UAS positions itself at a known elevation and position relative to the power line. For example, as the UAS flies over a power line, the magnetic field will reach a maximum value and then begin to decrease as the UAS moves away from the power line. After one sweep of a known distance, the UAS can return to where the magnetic field was the strongest. Based upon known characteristics of power lines and the magnetic readings, the UAS can determine the type of power line.

[00968] Once the current source has been identified, the UAS can change its elevation until the magnetic field is a known value that corresponds with an elevation above the identified power line. For example, as shown in FIG. 49, a magnetic field strength can be used to determine an elevation above the current source. The UAS can also use the measured magnetic field to position itself offset from directly above the power line. For example, once the UAS is positioned above the current source, the UAS can move laterally to an offset position from the current source. For example, the UAS can move to be 10 kilometers to the left or right of the current source.

[00969] The UAS can be programmed, via a computer 4606, with a flight path. In various implementations, once the UAS establishes its position, the UAS can use a flight path to reach its destination. In various implementations, the magnetic field generated by the transmission line is perpendicular to the transmission line. In these implementations, the vehicle will fly perpendicular to the detected magnetic field. In one example, the UAS can follow the detected power line to its destination. In this example, the UAS will attempt to keep the detected magnetic field to be close to the original magnetic field value. To do this, the UAS can change elevation or move laterally to stay in its position relative to the power line. For example, a power line that is rising in elevation would cause the detected magnetic field to increase in strength as the distance between the UAS and power line decreased. The navigation system of the UAS can detect this increased magnetic strength and increase the elevation of the UAS. In addition, on board instruments can provide an indication of the elevation of the UAS. The navigation system can also move the UAS laterally to the keep the UAS in the proper position relative to the power lines.

[00970] The magnetic field can become weaker or stronger, as the UAS drifts from its position of the transmission line. As the change in the magnetic field is detected, the navigation system can make the appropriate correction. For a UAS that only has a single DNV sensor, when the magnetic field had decreased by more than a predetermined amount the navigation system can make corrections. For example, the UAS can have an error budget such that the UAS will attempt to correct its course if the measured error is greater than the error budget. If the magnetic field has decreased, the navigation system can instruct the UAS to move to the left.

The navigation system can continually monitor the magnetic field to see if moving to the left corrected the error. If the magnetic field further decreased, the navigation system can instruct the UAS to fly to the right to its original position relative to the current source and then move further to the right. If the magnetic field decreased in strength, the navigation system can deduce that the UAS needs to decrease its altitude to increase the magnetic field. In this example, the UAS would originally be flying directly over the current source, but the distance between the current source and the UAS has increased due to the current source being at a lower elevation. Using this feedback loop of the magnetic field, the navigation system can keep the UAS centered or at an offset of the current source. The same analysis can be done when the magnetic field increases in strength. The navigation can maneuver until the measured magnetic field is within the proper range such that the UAS in within the flight path.

[00971] The UAS can also use the vector measurements from one or more DNV sensors to determine course corrections. The readings from the DNV sensor are vectors that indicate the direction of the sensed magnetic field. Once the UAS knows the location of the power line, as the magnitude of the sensed magnetic field decreases, the vector can provide an indication of the direction the UAS should move to correct its course. For example, the strength of the magnetic field can be reduced by a threshold amount from its ideal location. The magnetic vector of this field can be used to indicate the direction the UAS should correct to increase the strength of the magnetic field. In other words, the magnetic field indicates the direction of the field and the UAS can use this direction to determine the correct direction needed to increase the strength of the magnetic field, which could correct the UAS flight path to be back over the transmission wire.

[00972] Using multiple sensors on a single vehicle can reduce the amount of maneuvering that is needed or eliminate the maneuvering all together. Using the measured magnetic field from each of the multiple sensors, the navigation system can determine if the UAS needs to correct its course by moving left, right, up, or down. For example, if both DNV sensors are reading a stronger field, the navigation system can direct the UAS to increase its altitude. As another example if the left sensor is stronger than expected but the right sensor is weaker than expected, the navigation system can move the UAS to the left.

[00973] In addition to the current readings from the one or more sensors, a recent history of readings can also be used by the navigation system to identify how to correct the UAS course.

For example, if the right sensor had a brief increase in strength and then a decrease, while the left sensor had a decrease, the navigation system can determine that the UAS has moved to far to the left of the flight path and could correct the position of the UAS accordingly.

[00974] FIG. 46 illustrates a high-level block diagram of an example UAS navigation system 4600, according to some implementations of the subject technology. In some implementations, the UAS navigation system of the subject technology includes a number of DNV sensors 4602a, 4602b, and 4602c, a navigation database 4604, and a feedback loop that controls the UAS position and orientation. In other implementations, a vehicle can contain a navigation control that is used to navigate the vehicle. For example, the navigation control can change the vehicle’s direction, elevation, speed, etc. The DNV magnetic sensors 4602a-4602c have high sensitivity to magnetic fields, low C-SWAP and a fast settling time. The DNV magnetic field measurements allow the UAS to align itself with the power lines, via its characteristic magnetic field signature, and to rapidly move along power-line routes. Not all of the depicted components may be required, however, and one or more implementations may include additional components not shown in the figure. Variations in the arrangement and type of the components may be made, and additional components, different components, or fewer components may be provided.

[00975] FIG. 47 illustrates an example of a power line infrastructure. It is known that widespread power line infrastructures, such as shown in FIG. 47, connect cities, critical power system elements, homes and businesses. The infrastructure may include overhead and buried power distribution lines, transmission lines, railway catenary and 3rd rail power lines and underwater cables. Each element has a unique electro-magnetic and spatial signature. It is understood that, unlike electric fields, the magnetic signature is minimally impacted by manmade structures and electrical shielding. It is understood that specific elements of the infrastructure will have distinct magnetic and spatial signatures and that discontinuities, cable droop, power consumption and other factors will create variations in magnetic signatures that can also be leveraged for navigation.

[00976] Figures 48A and 48B illustrate examples of magnetic field distribution for overhead power lines and underground power cables. Both above-ground and buried power cables emit magnetic fields, which unlike electrical fields are not easily blocked or shielded. Natural Earth and other man-made magnetic field sources can provide rough values of absolute location. However, the sensitive magnetic sensors described here can locate strong man-made magnetic sources, such as power lines, at substantial distances. As the UAS moves, the measurements can be used to reveal the spatial structure of the magnetic source (point source, line source, etc.) and thus identify the power line as such. In addition, once detected the UAS can guide itself to the power line via its magnetic strength. Once the power line is located its structure is determined, and the power line route is followed and its characteristics are compared to magnetic way points to determine absolute location. Fixed power lines can provide precision location reference as the location and relative position of poles and towers are known. A compact on-board database can provide reference signatures and location data for waypoints. Not all of the depicted components may be required, however, and one or more implementations may include additional components not shown in the figure. Variations in the arrangement and type of the components may be made, and additional components, different components, or fewer components may be provided.

[00977] FIG. 49 illustrates examples of magnetic field strength of power lines as a function of distance from the centerline showing that even low current distribution lines can be detected to distances in excess of 10 km. Here it is understood that DNV sensors provide 0.01 uT sensitivity (le-10 T), and modeling results indicates that high current transmission line (e.g. with 1000 A -4000 A) can be detected over many tens of km. These strong magnetic sources allow the UAS to guide itself to the power lines where it can then align itself using localized relative field strength and the characteristic patterns of the power-line configuration as described below.

[00978] FIG. 50 illustrates an example of a UAS 5002 equipped with DNV sensors 5004 and 5006. FIG. 51 is a plot of a measured differential magnetic field sensed by the DNV sensors when in close proximity of the power lines. While power line detection can be performed with only a single DNV sensor precision alignment for complex wire configurations can be achieved using multiple arrayed sensors. For example, the differential signal can eliminate the influence of diurnal and seasonal variations in field strength. Not all of the depicted components may be required, however, and one or more implementations may include additional components not shown in the figure. Variations in the arrangement and type of the components may be made, and additional components, different components, or fewer components may be provided.

[00979] In various other implementations, a vehicle can also be used to inspect power transmission lines, power lines, and power utility equipment. For example, a vehicle can include one or more magnetic sensors, a magnetic waypoint database, and an interface to UAS flight control. The subject technology may leverage high sensitivity to magnetic fields of DNV magnetic sensors for magnetic field measurements. The DNV magnetic sensor can also be low cost, space, weight, and power (C-SWAP) and benefit from a fast settling time. The DNV magnetic field measurements allow UASs to align themselves with the power lines, and to rapidly move along power-line routes and navigate in poor visibility conditions and/or in GPS-denied environments. It is understood that DNV-based magnetic sensors are approximately 100 times smaller than conventional magnetic sensors and have a reaction time that that is approximately 100,000 times faster than sensors with similar sensitivity such as the EMDEX LLC Snap handheld magnetic field survey meter.

[00980] The fast settling time and low C-SWAP of the DNV sensor enables rapid measurement of detailed power line characteristics from low-C-SWAP UAS systems. In one or more implementations, power lines can be efficiently surveyed via small unmanned aerial vehicles (UAVs) on a routine basis over long distance, which can identify emerging problems and issues through automated field anomaly identification. In other implementations, a land based vehicle or submersible can be used to inspect power lines. Human inspectors are not required to perform the initial inspections. The inspections of the subject technology are quantitative, and thus are not subject to human interpretation as remote video solutions may be.

[00981] FIG. 52 illustrates an example of a measured magnetic field distribution for normal power lines 5204 and power lines with anomalies 5202 according to some implementations. The peak value of the measured magnetic field distribution, for the normal power lines, is in the vicinity of the centerline (e.g., d = 0). The inspection method of the subject technology is a highspeed anomaly mapping technique that can be employed for single and multi-wire transmission systems. The subject solution can take advantage of existing software modeling tools for analyzing the inspection data. In one or more implementations, the data of a normal set of power lines may be used as a comparison reference for data resulting from inspection of other power lines (e.g., with anomalies or defects). Damage to wires and support structure alters the nominal magnetic field characteristics and is detected by comparison with nominal magnetic field characteristics of the normal set of power lines. It is understood that the magnetic field measurement is minimally impacted by other structures such as buildings, trees, and the like. Accordingly, the measured magnetic field can be compared to the data from the normal set of power lines and the measured magnetic field’s magnitude and if different by a predetermined threshold the existence of the anomaly can be indicated. In addition, the vector reading between the difference data can also be compared and used to determine the existence of anomaly.

[00982] FIGs. 165 A and 165B are block diagrams of a system for detecting deformities in a transmission line in accordance with an illustrative embodiment. An illustrative system 100 includes a transmission line 16505 and a magnetometer 16530. The magnetometer can be included within a vehicle.

[00983] Current flows through the transmission line 16505 as indicated by the arrow labeled 16520. Figures 165 A and 165B illustrate the direction of a current through the transmission line 16505. As the current 16520 passes through the transmission line 16505 a magnetic field is generated 16525. The magnetometer 16530 can be passed along the length of the transmission line 16505. Figures 165 A and 165B include an arrow parallel to the length of the transmission line 16505 indicating the relative path of the magnetometer 16530. In alternative embodiments, any suitable path may be used. For example, in some embodiments in which the transmission line 16505 is curved, the magnetometer 16530 can follow the curvature of the transmission line 16505. In addition, the magnetometer 16530 does not have to remain at a constant distance from the transmission line 16505.

[00984] The magnetometer 16530 can measure the magnitude and/or direction of the magnetic field along the length of the transmission line 16505. For example, the magnetometer 16530 measures the magnitude and the direction of the magnetic field at multiple sample points along the length of the transmission line 16505 at the same orientation to the transmission line 16505 at the sample points. For instance, the magnetometer 16530 can pass along the length of the transmission line 16505 while above the transmission line 16505.

[00985] Any suitable magnetometer can be used as the magnetometer 16530. In some embodiments, the magnetometer uses one or more diamonds with NV centers. The magnetometer 16530 can have a sensitivity suitable for detecting changes in the magnetic field around the transmission line 16505 caused by deformities. In some instances, a relatively insensitive magnetometer 16530 may be used. In such instances, the magnetic field surrounding the transmission line 16505 should be relatively strong. For example, the magnetometer 16530 can have a sensitivity of about 10'9 Tesla (one nano-Tesla). Transmission lines can carry a large current, which allows detection of the magnetic field generated from the transmission line over a large distances. For example, for high current transmission lines, the magnetometer 16530 can be 10 kilometers away from the transmission source. The magnetometer 16530 can have any suitable measurement rate. For example, the magnetometer 16530 can measure the magnitude and/or the direction of a magnetic field at a particular point in space ten thousand times per second. In another example, the magnetometer 16530 can take a measurement fifty thousand times per second. Further description of operation of a DNV sensor is described in U.S. Patent

Application No. / ,_, entitled “Apparatus and Method for Hypersensitivity Detection of

Magnetic Field,” filed on the same day as this application, the contents of which are hereby incorporated by reference.

[00986] In some embodiments in which the magnetometer 16530 measures the direction of the magnetic field, the orientation of the magnetometer 16530 to the transmission line 16505 can be maintained along the length of the transmission line 16505. As the magnetometer 16530 passes along the length of the transmission line 16505, the direction of the magnetic field can be monitored. If the direction of the magnetic field changes or is different than an expected value, it can be determined that a deformity exits in the transmission line 16505.

[00987] In some embodiments, the magnetometer 16530 can be maintained at the same orientation to the transmission line 16505 because even if the magnetic field around the transmission line 16505 is uniform along the length of the transmission line 16505, the direction of the magnetic field is different at different points around the transmission line 16505. For example, referring to the magnetic field direction 16525 of Fig. 165 A, the direction of the magnetic field above the transmission line 16505 is pointing to the right of the transmission line 16505 (e.g., according to the “right-hand rule”). A vehicle carrying the magnetometer would know the magnetometer’s relative position to the transmission line 16505. For example, an aerial vehicle would know its relative position would be above or a known distance offset from the transmission line 16505, while a ground based vehicle would now its relative position to be below or a known offset from the transmission line 16505. Based upon the relative position of the magnetometer to the transmission line 16505, the direction magnetic vector can be monitored for indicating defects in the transmission line 16505.

[00988] In some embodiments in which the magnetometer 16530 measures magnitude of the magnetic field and not the direction of the magnetic field, the magnetometer 16530 can be located at any suitable location around the transmission line 16505 along the length of the transmission line 16505 and the magnetometer 16530 may not be held at the same orientation along the length of the transmission line 16505. In such embodiments, the magnetometer 16530 may be maintained at the same distance from the transmission line 16505 along the length of the transmission line 16505 (e.g., assuming the same material such as air is between the magnetometer 16530 and the transmission line 16505 along the length of the transmission line 16505).

[00989] Fig. 165A illustrates the system in which the transmission line 16505 does not contain a deformity. Fig. 165B illustrates in which the transmission line 16505 includes a defect 16535. The defect 16535 can be a crack in the transmission line, a break in the transmission line, a deteriorating portion of the transmission line, etc. A defect 16535 is a condition of the transmission line that affects the current flow through a defect free transmission line. As shown in Figure 165B, a portion of the current 16520 is reflected back from the defect 16535 as shown by the reflected current 16540. As in Figure 10B, the magnetic field direction 16525 corresponds to the current 16520. The reflected current magnetic field direction 16545 corresponds to the reflected current 16540. The magnetic field direction 16525 is opposite the reflected current magnetic field direction 16545 because the current 16520 travels in the opposite direction from the reflected current 16540. Accordingly, the magnetic field measured in the transmission line would be based upon both the current 16520 and the reflected current 16540. This magnetic field is different in magnitude and possibly direction from the magnetic field 16525. The difference between the magnetic fields 16525 and 16545 can be calculated and used to indicate the presence of the defect 16535. In some instances, as the magnetometer 16530 travels closer to the defect 16535, the magnitude of the detected magnetic field reduces. In some embodiments, it can be determined that the defect 16535 exists when the measured magnetic field is below a threshold value. In some embodiments, the threshold value may be a percentage of the expected value, such as ±5%, ±10%, ±15%, ±50%, or any other suitable portion of the expected value. In alternative embodiments, any suitable threshold value may be used.

[00990] In some embodiments in which the defect 16535 is a full break that breaks conductivity between the portions of the transmission line 16505, the magnitude of the current 16520 may be equal to or substantially similar to reflected current 16540. Thus, the combined magnetic field around the transmission line 16505 will be zero or substantially zero. That is, the magnetic field generated by the current 16520 is canceled out by the equal but opposite magnetic field generated by the reflected current 16540. In such embodiments, the defect 16535 may be detected using the magnetometer 16530 by comparing the measured magnetic field, which is substantially zero, to an expected magnetic field, which is a non-zero amount.

[00991] In some embodiments in which the defect 16535 allows some of the current 16520 to pass through or around the defect 16535, the magnitude of the reflected current 16540 is less than the magnitude of the current 16520. Accordingly, the magnitude of the magnetic field generated by the reflected current 16540 is less than the magnitude of the magnetic field generated by the current 16520. Although the magnitudes of the current 16520 and the reflected current 16540 may not be equal, the current magnetic field direction 16525 and the reflected current magnetic field direction 16545 are still opposite. Thus, the net magnetic field will be a magnetic field in the current magnetic field direction 16525. The magnitude of the net magnetic field is the magnitude of the magnetic field generated by the current 16520 reduced based upon the magnitude of the magnetic field generated by the reflected current 16540. As mentioned above, the magnetic field measured by the magnetometer 16530 can be compared against a threshold. Depending upon the severity, size, and/or shape of the defect 16535, the net magnetic field sensed by the magnetometer 16530 may or may not be less than (or greater than) the threshold value. Thus, the threshold value can be adjusted to adjust the sensitivity of the system. That is, the more that the threshold value deviates from the expected value, the larger the deformity in the transmission line 16505 is to cause the magnitude of the sensed magnetic field to be less than the threshold value. Thus, the closer that the threshold value is to the expected value, the finer, smaller, less severe, etc. deformities are detected by the system 100.

[00992] As mentioned above, the direction of the magnetic field around the transmission line 16505 can be used to sense a deformity in the transmission line 16505. Figure 166 illustrates current paths through a transmission line with a deformity 16635 in accordance with an illustrative embodiment. Figure 166 is meant to be illustrative and explanatory only and not meant to be limiting with respect to the functioning of the system.

[00993] A current can be passed through the transmission line 16605, as discussed above.

The current paths 16620 illustrate the direction of the current. As shown in Figure 166, the transmission line 16605 includes a deformity 16635. The deformity 16635 can be any suitable deformity, such as a crack, a dent, an impurity, etc. The current passing through the transmission line 16605 spreads uniformly around the transmission line 16605 in portions that do not include the deformity 16635. In some instances, the current may be more concentrated at the surface of the transmission line 16605 than at the center of the transmission line 16605.

[00994] In some embodiments, the deformity 16635 is a portion of the transmission line 16605 that does not allow or resists the flow of electrical current. Thus, the current passing through the transmission line 16605 flows around the deformity 16635. As shown in Fig. 165 A, the current magnetic field direction 16525 is perpendicular to the direction of the current 16520. Thus, as in Fig. 165 A, when the transmission line 16505 does not include a deformity, the direction of the magnetic field around the transmission line 16505 is perpendicular to the length of the transmission line 16505 all along the length of the transmission line 16505.

[00995] As shown in Figure 166, when the transmission line 16605 includes a deformity 16635 around which the current flows, the direction of the current changes, as shown by the current paths 16620. Thus, even though the transmission line 16605 is straight, the current flowing around the deformity 16635 is not parallel to the length of the transmission line 16605. Accordingly, the magnetic field generated by the current paths corresponding to the curved current paths 16620 is not perpendicular to the length of the transmission line 16605. Thus, as a magnetometer such as the magnetometer 16530 passes along the length of the transmission line 16605, a change in direction of the magnetic field around the transmission line 16605 can indicate that the deformity 16635 exits. As the magnetometer 16530 approaches the deformity 16635, the direction of the magnetic field around the transmission line 16605 changes from being perpendicular to the length of the transmission line 16605. As the magnetometer 16530 passes along the deformity 16635, the change in direction of the magnetic field increases and then decreases as the magnetometer 16530 moves away from the deformity 16635. The change in the direction of the magnetic field can indicate the location of the deformity 16635. In some instances, the transmission line 16605 may have a deformity that reflects a portion of the current, as illustrated in Figure 165B, and that deflects the flow of the current, as illustrated in Figure 166.

[00996] The size, shape, type, etc. of the deformity 16635 determines the spatial direction of the magnetic field surrounding the deformity 16635. In some embodiments, multiple samples of the magnetic field around the deformity 16635 can be taken to create a map of the magnetic field. In an illustrative embodiment, each of the samples includes a magnitude and direction of the magnetic field. Based on the spatial shape of the magnetic field surrounding the deformity 16635, one or more characteristics of the deformity 16635 can be determined, such as the size, shape, type, etc. of the deformity 16635. For instance, depending upon the map of the magnetic field, it can be determined whether the deformity 16635 is a dent, a crack, an impurity in the transmission line, etc. In some embodiments, the map of the magnetic field surrounding the deformity 16635 can be compared to a database of known deformities. In an illustrative embodiment, it can be determined that the deformity 16635 is similar to or the same as the closest matching deformity from the database. In an alternative embodiment, it can be determined that the deformity 16635 is similar to or the same as a deformity from the database that has a similarity score that is above a threshold score. The similarity score can be any suitable score that measures the similarity between the measured magnetic field and one or more known magnetic fields of the database.

[00997] In various implementations, a vehicle that includes one or magnetometers can navigate via the power lines that are being inspected. For example, the vehicle can navigate to n known position, e.g., a starting position, identify the presence of a power line based upon the sensed magnetic vector. Then the vehicle can determine the type of power line and further determine that the type of power line is the type that is to be inspected. The vehicle can then autonomously or semi-autonomously navigate via the power lines as described in detail above, while inspecting the power lines at the same time.

[00998] In various implementations, a vehicle may need to avoid objects that are in their navigation path. For example, a ground vehicle may need to maneuver around people or objects, or a flying vehicle may need to avoid a building or power line equipment. In these implementations, the vehicle can be equipment with sensors that are used to locate the obstacles that are to be avoided. Systems such as a camera system, focal point array, radar, acoustic sensors, etc., can be used to identify obstacles in the vehicles path. The navigation system can then identify a course correction to avoid the identified obstacles.

[00999] Power transmission lines can be stretched between two transmission towers. In these instances, the power transmission lines can sag between the two transmission towers. The power transmission line sag depends on the weight of the wire, tower spacing and wire tension, which varies with ambient temperature and electrical load. Excessive sagging can cause shorting when the transmission line comes into contact with brush or other surface structures. This can caused power transmission lines to fail.

[001000] Figure 167 illustrates power transmission line sag between transmission towers in accordance with an illustrative embodiment. A transmission line 16710 is shown with “normal” sag 16722. Here sag is determined based upon how far below the transmission line is from the tower height. The transmission line 16710 is stretched between a first tower 16702 and a second tower 16704. A second transmission line 16720 is shown with excessive sag. When this occurs the transmission line 16720 can come into contact with vegetation 16730 or other surface structures that can cause on or failure to the line.

[001001] A vector measurement made with a magnetometer mounted on a UAV can measure the wire sag as the UAV flies along the power lines. Figure 168 depicts the instantaneous measurement of the magnetic field at point X’ as the UAV flies at a fixed height above the towers. A larger horizontal (x) component of the magnetic field indicates more sag. Figure 169 depicts the variation in magnetic field components for the wire with nominal sag, and for the wire with excessive sag as the UAV transits between towers 1 and 2. The X and Z components for a transmission line under normal/nominal sag are shown (16908 and 16902 respectively). In addition, the X component 16906 and the Z component 16904 of a line experiencing excessive sag is also shown.

[001002] The cable sag may be measured by flying the UAV along the cable from tower to tower. Figure 169 shows the modulation in vector components of the magnetic field for different sag values. A look-up table can be constructed to retrieve the sag from these measurements for wires between each pair of towers along the UAV flight route. Alternatively a database of prior vector measurements can be compared with measurements. In general the flatter the curves the less sag. The exact value of the sag depends on the distance between towers and, which is measured by the UAV, and the angle of the vector at the tower. Combined with weather information and potentially historical data or transmission line sag models, the vector measurements can be used to determine if the power line is experiencing greater or lesser sag as expected. When this occurs, an indication that the power line is experiencing a sag anomaly can be indicated and/or reported.

[001003] The herein described subject matter sometimes illustrates different components contained within, or connected with, different other components. It is to be understood that such depicted architectures are merely exemplary, and that in fact many other architectures can be implemented which achieve the same functionality. In a conceptual sense, any arrangement of components to achieve the same functionality is effectively "associated" such that the desired functionality is achieved. Hence, any two components herein combined to achieve a particular functionality can be seen as "associated with" each other such that the desired functionality is achieved, irrespective of architectures or intermedial components. Likewise, any two components so associated can also be viewed as being "operably connected," or "operably coupled," to each other to achieve the desired functionality, and any two components capable of being so associated can also be viewed as being "operably couplable," to each other to achieve the desired functionality. Specific examples of operably couplable include but are not limited to physically mateable and/or physically interacting components and/or wirelessly interactable and/or wirelessly interacting components and/or logically interacting and/or logically interactable components.

[001004] With respect to the use of substantially any plural and/or singular terms herein, those having skill in the art can translate from the plural to the singular and/or from the singular to the plural as is appropriate to the context and/or application. The various singular/plural permutations may be expressly set forth herein for sake of clarity.

[001005] It will be understood by those within the art that, in general, terms used herein, and especially in the appended claims (e.g., bodies of the appended claims) are generally intended as "open" terms (e.g., the term "including" should be interpreted as "including but not limited to," the term "having" should be interpreted as "having at least," the term "includes" should be interpreted as "includes but is not limited to," etc.). It will be further understood by those within the art that if a specific number of an introduced claim recitation is intended, such an intent will be explicitly recited in the claim, and in the absence of such recitation no such intent is present. For example, as an aid to understanding, the following appended claims may contain usage of the introductory phrases "at least one" and "one or more" to introduce claim recitations. However, the use of such phrases should not be construed to imply that the introduction of a claim recitation by the indefinite articles "a" or "an" limits any particular claim containing such introduced claim recitation to inventions containing only one such recitation, even when the same claim includes the introductory phrases "one or more" or "at least one" and indefinite articles such as "a" or "an" (e.g., "a" and/or "an" should typically be interpreted to mean "at least one" or "one or more"); the same holds true for the use of definite articles used to introduce claim recitations. In addition, even if a specific number of an introduced claim recitation is explicitly recited, those skilled in the art will recognize that such recitation should typically be interpreted to mean at least the recited number (e.g., the bare recitation of "two recitations," without other modifiers, typically means at least two recitations, or two or more recitations). Furthermore, in those instances where a convention analogous to "at least one of A, B, and C, etc." is used, in general such a construction is intended in the sense one having skill in the art would understand the convention (e.g., "a system having at least one of A, B, and C" would include but not be limited to systems that have A alone, B alone, C alone, A and B together, A and C together, B and C together, and/or A, B, and C together, etc.). In those instances where a convention analogous to "at least one of A, B, or C, etc." is used, in general such a construction is intended in the sense one having skill in the art would understand the convention (e.g., "a system having at least one of A, B, or C" would include but not be limited to systems that have A alone, B alone, C alone, A and B together, A and C together, B and C together, and/or A, B, and C together, etc.). It will be further understood by those within the art that virtually any disjunctive word and/or phrase presenting two or more alternative terms, whether in the description, claims, or drawings, should be understood to contemplate the possibilities of including one of the terms, either of the terms, or both terms. For example, the phrase "A or B" will be understood to include the possibilities of "A" or "B" or "A and B." Further, unless otherwise noted, the use of the words “approximate,” “about,” “around,” “substantially,” etc., mean plus or minus ten percent.

[001006] The foregoing description of illustrative embodiments has been presented for purposes of illustration and of description. It is not intended to be exhaustive or limiting with respect to the precise form disclosed, and modifications and variations are possible in light of the above teachings or may be acquired from practice of the disclosed embodiments. It is intended that the scope of the invention be defined by the claims appended hereto and their equivalents.

Claims (31)

1. WHAT IS CLAIMED IS:

   1. A system for magnetic detection, comprising: a diamond nitrogen-vacancy (DNV) sensor comprising: a nitrogen vacancy (NV) diamond material comprising a plurality of NV centers; a radio frequency (RF) excitation source configured to provide RF excitation to the NV diamond material; an optical excitation source configured to provide optical excitation to the NV diamond material; an optical detector configured to receive an optical signal emitted by the NV diamond material, wherein the optical signal is based on hyperfine states of the NV diamond material; and a controller configured to detect a gradient of the optical signal based on the hyperfine states emitted by the NV diamond material.
2. 2. The system of claim 1, wherein the DNV sensor further comprises a reflector positioned about the diamond to reflect a portion of light emitted from the diamond.
3. 3. The system of claim 1, wherein the DNV sensor further comprises: a magnetic field generator configured to generate a magnetic field; wherein the controller is further configured to: control the magnetic field generator to apply a time varying magnetic field at the NV diamond material, determine a magnitude and direction of the magnetic field at the NV diamond material based on a received light detection signal from the optical detector; and determine a magnetic vector anomaly due to an object based on the determined magnitude and direction of the magnetic field according to a frequency dependent attenuation of the time varying magnetic field.
4. 4. The system of claim 1, wherein the DNV sensor further comprises: a magnetic field generator comprising at least two magnetic field generators including a first magnetic field generator configured to generate a first magnetic field and a second magnetic field generator configured to generate a second magnetic field; wherein the controller is further configured to: modulate a first code packet and control the first magnetic field generator to apply a first time varying magnetic field at the NV diamond material based on the modulated first code packet, modulate a second code packet and control the second magnetic field generator to apply a second time varying magnetic field at the NY diamond material based on the modulated second code packet, wherein the first code packet and the second code packet are binary sequences which have a low cross correlation with each other, and each of the binary sequences has a good autocorrelation.
5. 5. The system of claim 4, wherein a direction of the first time varying magnetic field at the NV diamond material is different from a direction of the second time varying magnetic field at the NV diamond material.
6. 6. The system of claim 4, wherein the controller is further configure to: receive first light detection signals from the optical detector based on the optical signal emitted by the NV diamond material based on the first code packet transmitted to the NV diamond material, and receive second light detection signals from the optical detector based on the optical signal emitted by the NV diamond material based on the second code packet transmitted to the NV diamond material simultaneous with the first code packet being transmitted to the NV diamond material; apply matched filters to the received first and second light detection signals to demodulate the first and second code packets, determine a magnitude and direction of the first magnetic field and the second magnetic field at the NV diamond material based on the demodulated first and second code packets; and determine a magnetic vector anomaly based on the determined magnitude and direction of the first magnetic field and the second magnetic field.
7. 7. The system of claim 4, wherein the first and second code packets are modulated by continuous phase modulation.
8. 8. The system of claim 4, wherein the first and second code packets are modulated by MSK frequency modulation.
9. 9. The system of claim 4, wherein the controller is further configured to control the RF excitation source and the optical excitation source to provide a sequence of pulses to the magneto-optical defect center material.
10. 10. The system of claim 1, further comprising: a transmitting device comprising: a first processor configured to transmit data to a transmitter; and the transmitter, wherein the transmitter is configured to transmit the data via a magnetic field.
11. 11. The system of claim 10, further comprising: a receiving device comprising: the DNV sensor configured to detect the magnetic field; and a second processor configured to decipher the data from the detected magnetic field.
12. 12. The system of claim 11, wherein the first processor is further configured to: receive a first data stream comprising the data; and interleave the data into a plurality of second data streams, and wherein the transmitter is configured to transmit each of the second data streams on one of a plurality of channels.
13. 13. The system of claim 12, wherein each of the plurality of channels comprises one of a plurality of magnetic fields.
14. 14. The system of claim 13, wherein each of the plurality of magnetic fields is orthogonal to one another.
15. 15. The system of claim 12, wherein the magnetometer is configured to detect the magnetic field in a plurality of directions.
16. 16. The system of claim 15, wherein the plurality of directions are tetrahedrally arranged.
17. 17. The system of claim 15, wherein the second processor is configured to: receive a plurality of signals from the magnetometer, wherein each of the plurality of signals corresponds to one of the plurality of directions; decipher each of the plurality of second data streams from the plurality of signals; and de-interleave the plurality of second data streams to determine the data.
18. 18. The system of claim 12, wherein to transmit the data via the magnetic field, the transmitter is configured to transmit two data streams via two magnetic fields, and wherein each of the two data streams corresponds to one of the two magnetic fields.
19. 19. The system of claim 12, wherein to transmit the data via a magnetic field, the transmitter is configured to transmit three data streams via three magnetic fields, wherein each of the three data streams corresponds to one of the three magnetic fields.
20. 20. The system of claim 12, wherein the first processor is further configured to: receive a first data stream comprising the data; interleave the data into a plurality of second data streams; and append a synchronization sequence to each of the plurality of second data streams to form a plurality of third data streams, and wherein the transmitter is configured to transmit each of the third data streams on one of a plurality of channels.
21. 21. The system of claim 20, wherein the magnetometer is configured to detect the magnetic field in a plurality of directions, wherein the plurality of directions are orthogonal to one another; and wherein the second processor is configured to: receive a plurality of signals from the magnetometer, wherein each of the plurality of signals corresponds to one of the plurality of directions; decipher each of the plurality of third data streams from the plurality of signals by detecting the sequence stream; and interleave the plurality of third data streams to determine the data.
22. 22. The system of claim 1, further comprising: a first magnetic field sensor that includes the DNV sensor, a second magnetic field sensor that includes a second DNV sensor, and a position encoder component comprising a magnetic region configured to produce a magnetic field gradient from a first end of the magnetic region to the second end of the magnetic region, wherein the first magnetic field sensor and the second magnetic field sensor are separated by a distance that is less than a length of the magnetic region.
23. 23. The system of claim 22, wherein the magnetic region comprises a ferromagnetic component having a cross-section at the first end of the magnetic region that is smaller than a cross-section at the second end of the magnetic region.
24. 24. The system of claim 22, wherein the magnetic region comprises a magnetic polymer having a magnetic particle concentration at the first end of the magnetic region that is smaller than a magnetic particle concentration at the second end of the magnetic region.
25. 25. The system of claim 22, further comprising a third magnetic field sensor and a fourth magnetic field sensor.
26. 26. The system of claim 22, wherein the position encoder component is a rotary position encoder.
27. 27. The system of claim 22, wherein the position encoder component is a linear position encoder.
28. 28. The system of claim 22, wherein the position encoder component further comprises a plurality of the magnetic regions configured to produce a magnetic field gradient from a first end of the magnetic region to the second end of the magnetic region arranged end to end on the position encoder component.
29. 29. The system of claim 1, further comprising an acoustic transmitter configured to transmit an acoustic signal through a fluid with dissolved ions, wherein the DNV sensor is configured to detect the acoustic signal through the fluid.
30. 30. The system of claim 1, further comprising an acoustic transmitter configured to transmit an acoustic signal through a fluid with dissolved ions, wherein the DNV sensor is configured to detect the acoustic signal through the fluid.
31. 31. The system of claim 1, further comprising: a vehicle that includes the DNV sensor, wherein the DNV sensor is configured to detect a magnetic vector or a magnetic field; one or more electronic processors configured to: receive the magnetic vector of the magnetic field from the DNV sensor; and determine a presence of a current source based upon the magnetic vector; and a navigation control configured to navigate the vehicle based upon the presence of the current source and the magnetic vector.