US20150212166A1 - Magnetoresistive sensor and gradiometer - Google Patents

Magnetoresistive sensor and gradiometer Download PDF

Info

Publication number
US20150212166A1
US20150212166A1 US14/424,045 US201214424045A US2015212166A1 US 20150212166 A1 US20150212166 A1 US 20150212166A1 US 201214424045 A US201214424045 A US 201214424045A US 2015212166 A1 US2015212166 A1 US 2015212166A1
Authority
US
United States
Prior art keywords
magnetoresistive sensor
magnetoresistive
noise
sensor
circuit
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Abandoned
Application number
US14/424,045
Other languages
English (en)
Inventor
Akihiko Kandori
Yusuke Seki
Ryuzo KAWABATA
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Hitachi Ltd
Original Assignee
Hitachi Ltd
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Hitachi Ltd filed Critical Hitachi Ltd
Assigned to HITACHI, LTD. reassignment HITACHI, LTD. ASSIGNMENT OF ASSIGNORS INTEREST (SEE DOCUMENT FOR DETAILS). Assignors: KANDORI, AKIHIKO, KAWABATA, RYUZO, SEKI, YUSUKE
Publication of US20150212166A1 publication Critical patent/US20150212166A1/en
Abandoned legal-status Critical Current

Links

Images

Classifications

    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
    • G01R33/00—Arrangements or instruments for measuring magnetic variables
    • G01R33/02—Measuring direction or magnitude of magnetic fields or magnetic flux
    • G01R33/06—Measuring direction or magnitude of magnetic fields or magnetic flux using galvano-magnetic devices
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
    • G01R33/00—Arrangements or instruments for measuring magnetic variables
    • G01R33/02—Measuring direction or magnitude of magnetic fields or magnetic flux
    • G01R33/06—Measuring direction or magnitude of magnetic fields or magnetic flux using galvano-magnetic devices
    • G01R33/09—Magnetoresistive devices
    • A—HUMAN NECESSITIES
    • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
    • A61B—DIAGNOSIS; SURGERY; IDENTIFICATION
    • A61B5/00—Measuring for diagnostic purposes; Identification of persons
    • A61B5/05—Detecting, measuring or recording for diagnosis by means of electric currents or magnetic fields; Measuring using microwaves or radio waves 
    • A61B5/055—Detecting, measuring or recording for diagnosis by means of electric currents or magnetic fields; Measuring using microwaves or radio waves  involving electronic [EMR] or nuclear [NMR] magnetic resonance, e.g. magnetic resonance imaging
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
    • G01R33/00—Arrangements or instruments for measuring magnetic variables
    • G01R33/0005—Geometrical arrangement of magnetic sensor elements; Apparatus combining different magnetic sensor types
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
    • G01R33/00—Arrangements or instruments for measuring magnetic variables
    • G01R33/0023—Electronic aspects, e.g. circuits for stimulation, evaluation, control; Treating the measured signals; calibration
    • G01R33/0041—Electronic aspects, e.g. circuits for stimulation, evaluation, control; Treating the measured signals; calibration using feed-back or modulation techniques
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
    • G01R33/00—Arrangements or instruments for measuring magnetic variables
    • G01R33/02—Measuring direction or magnitude of magnetic fields or magnetic flux
    • G01R33/022—Measuring gradient

Definitions

  • This invention relates to a magnetoresistive sensor and a gradiometer using the same.
  • Magnetic resistance (hereinafter, abbreviated as MR) sensors are inexpensive, small, and highly sensitive, and widely used for contactless revolution detection and position detection.
  • the MR sensors include giant magnetoresistance (hereinafter, abbreviated as GMR) sensors, tunnel magnetoresistance (hereinafter, abbreviated as TMR) sensors, and an-isotropic magnetoresistance (hereinafter, abbreviated as AMR) sensors.
  • GMR giant magnetoresistance
  • TMR tunnel magnetoresistance
  • AMR an-isotropic magnetoresistance
  • the mobile devices such as cell phones and PDA (personal digital assistant) have been widespread and the mobile devices contain direction sensors using the MR sensors and may be used as navigation systems using position information by GPS (Global Positioning System).
  • GPS Global Positioning System
  • high-sensitive magnetism detection technologies are not necessarily required.
  • the direction sensor detects an absolute direction with reference to geomagnetism and does not require ultrasensitive magnetism detection, and, even in encode application of revolution detection and position detection, uses a magnet as a reference signal and the ultrasensitive magnetism detection is not essential.
  • biomagnetic fields medical devices including magnetocardiograph and magnetocephalograph that detect weak and low-frequency magnetic fields generated from electrical activity of living hearts and brains (hereinafter, referred to as “biomagnetic fields”) have been recently started to be used at medical sites.
  • biomagnetic fields a superconducting quantum interference device (hereinafter, referred to as SQUID) is used as the ultrasensitive magnetic sensor.
  • SQUID superconducting quantum interference device
  • the SQUID is a magnetic sensor using a superconductive phenomenon and has a structure with Josephson junction. Accordingly, the SQUID requires cooling by refrigerant (liquid helium or liquid nitrogen) and is placed within a cryostat in which the refrigerant is stored.
  • the SQUID is the ultrasensitive magnetic sensor, but there are problems that handling is complicated and it is impossible to make the magnetic sensor sufficiently closer to the living organism because the sensor is placed within the cryostat.
  • the sensitivity of the MR sensor at the lower frequency (100 Hz or less, particularly, 30 Hz or less) containing many biologically-originated signal components is important.
  • the noise determining the sensitivity in the low-frequency region includes two kinds of noise of white noise and 1/f noise. These two kinds of noise is not determined only by the noise generated by the MR sensor, but determined as system noise (sensitivity) by preamplifier noise and a combination with other operation circuits.
  • NPL 1 describes that set/reset pulse is applied to the MR sensor, magnetization of magnetoresistive elements is inverted, resulting alternating-current signals are detected, and thereby, the 1/f noise originated from the MR sensor is reduced.
  • NPL 1 Rev. Sci. Instrum. 82, 094703, 2011
  • NPL 2 Rev. Sci. Instrum. 80, 036102, 2009
  • an object of the invention is to reduce 1/f noise and white noise at the same time by integrally reducing noise of an MR sensor and noise of an operation circuit part.
  • a magnetoresistive sensor includes a plurality of magnetoresistive sensor parts each having a bridge circuit in which four magnetoresistive elements are connected, wherein outputs of the respective magnetoresistive sensor parts are connected in parallel to one another to an input of an amplifier circuit.
  • noise originated from an MR sensor may be reduced by a simple configuration.
  • FIG. 1 is a circuit diagram of an MR sensor in related art.
  • FIG. 2 is a circuit diagram of an MR sensor 100 according to embodiment 1.
  • FIG. 3 shows measurement results of system noise measured using an actual AMR sensor with respect to the MR sensor 100 according to embodiment 1.
  • FIGS. 4( a ) and 4 ( b ) exemplify an arrangement of magnetoresistive sensor parts 105 .
  • FIG. 5 is a circuit diagram of an MR sensor 100 according to embodiment 2.
  • FIG. 6 shows measurement results of system noise measured using an actual AMR sensor with respect to the MR sensor 100 according to embodiment 2.
  • FIG. 7 is a circuit diagram of an MR sensor 100 according to embodiment 3.
  • FIG. 8 shows measurement results of system noise measured using an actual AMR sensor with respect to the MR sensor 100 according to embodiment 3.
  • FIG. 9 is a circuit diagram of an MR sensor 100 according to embodiment 4.
  • FIG. 10 shows measurement results of system noise measured using an actual AMR sensor with respect to the MR sensor 100 according to embodiment 4.
  • FIG. 11 is a circuit diagram of an MR sensor 100 according to embodiment 5.
  • FIG. 12 is a circuit diagram of an MR sensor 100 according to embodiment 6.
  • FIG. 13 is a circuit diagram of an MR sensor 100 according to embodiment 7.
  • FIG. 14 is a circuit diagram of an MR sensor 100 according to embodiment 8.
  • FIG. 15 shows a configuration of a gradiometer 1500 according to embodiment 9.
  • FIG. 1 is a circuit diagram of an MR sensor in related art.
  • the MR sensor in related art has a bridge circuit (magnetoresistive sensor part 105 ) including magnetoresistive elements 101 - 1 , 101 - 2 , 101 - 3 , 101 - 4 and detects a magnetic field by minute resistance change due to a varying magnetic field.
  • a direct-current power source 102 applies a direct-current voltage as a drive voltage of the bridge circuit 105 .
  • a preamplifier 103 amplifies the voltage between both ends of the bridge circuit 105 and outputs it from an output terminal 104 .
  • thermal noise due to resistance components of the MR sensor becomes larger noise of the whole system and high-sensitivity detection of the magnetic field is difficult.
  • FIG. 2 is a circuit diagram of an MR sensor 100 according to embodiment 1 of the invention.
  • the MR sensor 100 includes a plurality of the magnetoresistive sensor parts 105 shown in FIG. 1 , and the outputs of the respective magnetoresistive sensor parts 105 are connected to the input of the preamplifier 103 in parallel to one another.
  • the four magnetoresistive sensor parts 105 - 1 , 105 - 2 , 105 - 3 , 105 - 4 are exemplified, however, the number of magnetoresistive sensor parts 105 is not limited to that.
  • the effective resistance of the parallel-connected magnetoresistive sensor parts 105 as a whole is one Nth of the resistance between both ends of the individual magnetoresistive sensor parts 105 .
  • the thermal noise Vr of the MR sensor 100 is calculated by the following formula 1.
  • k is the Boltzmann constant
  • R is the resistance between both ends of the magnetoresistive sensor part 105
  • T is an absolute temperature.
  • the N magnetoresistive sensor parts 105 are parallel-connected and the effective resistance is made to be one Nth, and thereby, the thermal noise (shot noise) generated from the resistance of the MR sensor 100 is one N 1/2 th. That is, the outputs of the plurality of magnetoresistive sensor parts 105 are parallel-connected to the input of the preamplifier 103 , and thereby, the thermal noise originated from the MR sensor may be reduced and the magnetic field may be detected with high sensitivity.
  • FIG. 2 the case where there are the four magnetoresistive sensor parts 105 is exemplified, however, in order to exhibit sensitivity that enables measurement of the biomagnetic field, it is desirable to connect ten or more of the magnetoresistive sensor parts 105 in parallel.
  • FIG. 3 shows measurement results of system noise measured using an actual AMR sensor with respect to the MR sensor 100 according to the embodiment 1.
  • Sign 301 denotes system noise measured using the configuration in FIG. 1 and sign 302 denotes system noise measured using the configuration in FIG. 2 .
  • Signs 303 and 304 denote white noise in the respective measurement results.
  • the white noise 303 was 35 pT/Hz 1/2 and the white noise 304 was 20 pT/Hz 1/2 .
  • FIG. 4 exemplifies an arrangement of the magnetoresistive sensor parts 105 .
  • FIG. 4( a ) is a top view and FIG. 4 (b) is a side view.
  • the magnetoresistive sensor parts 105 are arranged so that sensitivity directions maybe the same as shown in FIG. 4 .
  • the magnetoresistive sensor parts 105 having detection sensitivity in the direction perpendicular to the plane of paper are arranged on a substrate 401 .
  • the preamplifier 103 (not shown) is provided and power supply and signal output of the preamplifier 103 are connected to an external device through a connector part 402 .
  • the preamplifier 103 is desirably provided on the substrate 401 in view of the mounting space, however, not limited to that.
  • FIG. 4 shows the example in which the 24 magnetoresistive sensor parts 105 - 1 to 105 - 24 are arranged on the substrate 401 .
  • the magnetoresistive sensor parts 105 have parallelepiped shapes and the sensitivity direction perpendicular to the plane of paper as shown in FIG. 4 , for example, in order to place as many magnetoresistive sensor parts 105 as possible, they are arranged on the substrate 401 having a size of a diameter of about 15 mm so that the sensitive directions of the magnetic fields may be the same.
  • the system noise Vn of the MR sensor 100 can be expressed by the following formula 2. As shown in formula 2, regarding the system noise Vn, when the thermal noise Vr due to the resistance of the magnetoresistive sensor parts 105 is smaller, the voltage noise Va of the preamplifier 103 is predominant. In the embodiment 2, as a method of reducing the voltage noise Va of the preamplifier 103 , a configuration in which a plurality of the preamplifiers 103 are parallel-connected is employed.
  • Vn ( Vr 2 +Va 2 ) 1/2 formula 2
  • FIG. 5 is a circuit diagram of the MR sensor 100 according to the embodiment 2.
  • the preamplifiers 103 are provided for the respective magnetoresistive sensor parts 105 and the outputs of the respective magnetoresistive sensor parts 105 are input to the respective corresponding preamplifiers 103 .
  • the outputs of the respective preamplifiers 103 are parallel connected by an adder, and input to an amplifier 501 .
  • the voltage noise Va of the preamplifiers 103 decreases to one N 1/2 th as a whole.
  • the preamplifiers 103 are parallel connected in addition to the magnetoresistive sensor parts 105 , and thereby, the system noise Vn expressed in formula 2 may be integrally reduced.
  • FIG. 6 shows measurement results of the system noise measured using an actual AMR sensor with respect to the MR sensor 100 according to the embodiment 2.
  • Sign 601 denotes system noise measured using the configuration in FIG. 1 and sign 602 denotes system noise measured using the configuration in FIG. 5 .
  • Signs 603 and 604 denote white noise in the respective measurement results.
  • the white noise 603 was 35 pT/Hz 1/2 and the white noise 604 was 17 pT/Hz 1/2 .
  • the white noise 604 is decreased to be lower than the white noise 304 shown in FIG. 3 . That is, as expressed in the theoretical formula of the formula 2, it is known that the preamplifiers 103 are parallel-connected and the voltage noise Va of the preamplifiers 103 is reduced, and thereby, the system noise can be reduced to be about one half or less as a whole.
  • the magnetoresistive sensor parts 105 are parallel-connected and the preamplifiers 103 are further parallel-connected, and thereby, the white noise of the system noise may be reduced.
  • the white noise may be reduced.
  • FIG. 6 there is a problem that 1/f noise at 10 Hz or less remains higher. It is considered that this is because the white noise is reduced by parallel connection of the magnetoresistive sensor parts 105 , and the 1/f noise becomes obvious. Accordingly, in embodiment 3 of the invention, a method of reducing the 1/f noise using set/reset signals will be explained.
  • FIG. 7 is a circuit diagram of an MR sensor 100 according to the embodiment 3.
  • the MR sensor 100 in the embodiment 3 includes set/reset circuits 701 for the respective magnetoresistive sensor parts 105 .
  • the circuit configuration in which the set/reset circuits 701 are provided in addition to the circuit configuration of embodiment 1 is exemplified, however, the same configuration may be provided in embodiment 2 and the number of magnetoresistive sensor parts 105 is not limited to four.
  • the set/reset circuits 701 - 1 to 701 - 4 are provided in correspondence with the four magnetoresistive sensor parts 105 - 1 to 105 - 4 , respectively, and the respective set/reset circuits 701 - 1 to 701 - 4 are parallel-connected.
  • An alternating-current signal generator 703 supplies an alternating current (several kilohertz to several tens of kilohertz) to the respective set/reset circuits 701 - 1 to 701 - 4 .
  • the respective set/reset circuits 701 - 1 to 701 - 4 include coils that generate magnetic fields using the alternating current and apply them to the magnetoresistive elements 101 .
  • the circuits are adapted so that, when the magnetic fields are applied to the magnetoresistive elements 101 , the magnetization directions of the magnetoresistive elements 101 may be the same direction. Therefore, the magnetization directions of the magnetoresistive elements 101 are changed by the alternating current in response to its frequency, and thereby, an effect of cancelling the 1/f noise due to fluctuations in magnetization direction may be exhibited.
  • the output of the preamplifier 103 is connected to a lock-in amplifier 702 .
  • the lock-in amplifier 702 detects the output of the preamplifier 103 using the alternating current or a synchronizing signal (TTL signal) output by the alternating-current signal generator 703 as a reference signal 704 , and outputs a detection result from the output terminal 104 .
  • TTL signal a synchronizing signal
  • FIG. 8 shows measurement results of system noise measured using an actual AMR sensor with respect to the MR sensor 100 according to the embodiment 3.
  • Sign 801 denotes system noise measured using the configuration in FIG. 1 and sign 802 denotes system noise measured using the configuration in FIG. 7 .
  • Signs 803 and 804 denote white noise in the respective measurement results.
  • the white noise 803 was 35 pT/Hz 1/2 and the white noise 804 was 20 pT/Hz 1/2 . That is, the same effect as that of embodiment 1 was obtained with respect to white noise.
  • the system noise 802 is also lower in the low-frequency region (10 Hz or less), and the 1/f noise is reduced in this region.
  • the MR sensor 100 may reduce the white noise by parallel connection of the magnetoresistive sensor parts 105 , reduce the 1/f noise that becomes obvious thereby using the set/reset circuits 701 , and improve the sensitivity to the level at which the biomagnetic field can be measured.
  • the preamplifiers 103 are parallel-connected like embodiment 2 for reduction of the thermal noise Va of the preamplifiers 103 .
  • preamplifier current noise In flows to the magnetoresistive sensor parts 105 in the amount corresponding to the number of preamplifiers 103 , and voltage noise is generated due to the resistance of the magnetoresistive sensor parts 105 .
  • provision of many preamplifiers 103 is impractical. Accordingly, in embodiment 4 of the invention, a configuration in which a plurality of magnetoresistive sensor parts 105 are parallel-connected and only one preamplifier 103 is provided for reduction of the noise of the preamplifier 103 will be explained.
  • FIG. 9 is a circuit diagram of an MR sensor 100 according to the embodiment 4.
  • the MR sensor 100 in the embodiment 4 includes a step-up transformer 901 between the magnetoresistive sensor parts 105 and the preamplifier 103 .
  • the respective magnetoresistive sensor parts 105 are parallel-connected to the primary side of the step-up transformer 901 , and the secondary side is input to the preamplifier 103 .
  • the rest of the configuration is the same as that of embodiment 3.
  • the magnetization direction of the magnetoresistive sensor part 105 is inverted in response to the frequency of the alternating-current signal generator 703 by the action of the set/reset circuit 701 , and the output of the magnetoresistive sensor part 105 is an alternating-current signal.
  • the step-up transformer 901 uses this to boost the output of the magnetoresistive sensor part 105 .
  • the step-up transformer 901 forms a ten-fold amplification booster circuit using 100-turn winding at the primary side and 1000-turn winding at the secondary side, and thereby, the noise of the preamplifier 103 may be made effectively negligible. It is necessary to make the resistance value of the primary-side winding of the step-up transformer 901 sufficiently smaller than the resistance between both sides of the magnetoresistive sensor part 105 and suppress the influence of white noise by the primary-side winding resistance. Further, it is necessary to set the inductance of the primary-side winding to be sufficiently higher to make the impedance of the alternating-current signals higher so that the outputs of the respective magnetoresistive sensor parts 105 may not be short-circuited as the alternating-current signals. Accordingly, as the core of the step-up transformer 901 , a member with higher permeability such as ferrite is desirably used.
  • FIG. 10 shows measurement results of system noise measured using an actual AMR sensor with respect to the MR sensor 100 according to the embodiment 4.
  • Sign 1001 denotes system noise measured using the configuration in FIG. 1 and sign 1002 denotes system noise measured using the configuration in FIG. 9 .
  • Signs 1003 and 1004 denote white noise in the respective measurement results.
  • the white noise 1003 was 35 pT/Hz 1/2 and the white noise 1004 was 17 pT/Hz 1/2 .
  • the input to the preamplifier 103 is amplified in advance by the step-up transformer 901 using the alternating-current signals generated using the set/reset circuits 701 , and thereby, the noise of the preamplifier 103 maybe relatively reduced and, even when only one preamplifier 103 is provided, the influence of the noise may be effectively suppressed.
  • the configuration of the preamplifier 103 is simpler and the oscillation may be suppressed and the power consumption may be suppressed.
  • the amplification by the step-up transformer 901 is possible if the input to the step-up transformer 901 is the alternating-current signal, and thus, it is considered that, in place of the set/reset circuits 701 , the direct-current power source 102 is replaced by an alternating-current power source.
  • the noise of the preamplifier 103 may be suppressed by the effect of the step-up transformer 901 , but the magnetization directions of the magnetoresistive elements 101 remain fixed. Therefore, it is necessary to note that the effect of reducing the 1/f noise due to fluctuations is not exerted.
  • the configurations for reduction of white noise and 1/f noise are explained.
  • the actual measuring object may be e.g., an object having a temperature like a living organism or a metal material for non-destructive inspection (with higher heat conductivity).
  • the temperatures of the magnetoresistive sensor parts 105 differ depending on the locations in which they are placed and the sensitivity of the respective magnetoresistive sensor parts 105 varies due to temperature fluctuations, and thus, the 1/f noise and the white noise may increase.
  • the fluctuations in sensor sensitivity are generated due to temperature disturbance different from that due to the circuit configuration itself, and thus, it is considered that it is necessary to separately provide a configuration for suppressing that. Accordingly, in embodiment 5 of the invention, a configuration of suppressing the above described fluctuations in sensor sensitivity will be explained.
  • FIG. 11 is a circuit diagram of an MR sensor 100 according to the embodiment 5.
  • the MR sensor 100 in the embodiment 5 includes a feedback circuit in addition to the configurations explained in embodiments 1 to 4.
  • a configuration in which the feedback circuit is provided in addition to the circuit configuration explained in embodiment 4 is exemplified, however, the feedback circuit may be provided in the circuit configurations of the other embodiments.
  • the feedback circuit is a circuit that feeds back the output of the preamplifier 103 to the magnetoresistive elements 101 as the magnetic field applied to the magnetoresistive elements 101 , and has a feedback resistor 1101 and feedback coils 1102 .
  • the feedback coils 1102 are provided the respective magnetoresistive sensor parts 105 (feedback coils 1102 - 1 to 1102 - 4 in FIG. 11 ), receive signals between the output of the preamplifier 103 and the input of the lock-in amplifier 702 , generate magnetic fields using them, and feed them back to the magnetoresistive elements 101 .
  • the feedback resistor 1101 is provided between the output of the preamplifier 103 and the feedback coils 1102 .
  • the respective feedback coils 1102 are parallel-connected, however, they may be series-connected.
  • a phase adjustment circuit may be inserted at the downstream of the feedback circuits 1102 , at the downstream of the preamplifier 103 or in the step-up transformer 901 itself for adjustment.
  • the feedback circuits are provided and the output of the preamplifier 103 is fed back to the magnetoresistive elements 101 , and thereby, the influences of the temperature differences depending on the positions of the magnetoresistive sensor parts 105 and the sensitivity fluctuations due to the temperature of the measuring object may be suppressed.
  • the configuration is effective when the magnetoresistive sensor parts 105 are planarly (spatially) arranged and the temperatures differ in the respective magnetoresistive sensor parts 105 .
  • step-up transformers 901 In the step-up transformers 901 explained in embodiments 4 and 5, it is necessary to make the winding impedance higher as explained in embodiment 4. For the purpose, it is necessary to use a member having a larger size of several centimeters or more with higher permeability as the core of the step-up transformer 901 . It is difficult to wind 1000 turns or more of the secondary winding in the step-up transformer 901 with the larger core in consideration of attachment to the substrate 401 shown in FIG. 4 . Accordingly, in embodiment 6 of the invention, a configuration in which the amplification factor is improved while the size of the step-up transformer 901 is suppressed will be explained.
  • FIG. 12 is a circuit diagram of an MR sensor 100 according to the embodiment 6.
  • a capacitor 1201 forming a resonance circuit with the secondary-side coil is provided at the secondary side of the step-up transformer 901 .
  • the secondary-side inductance of the step-up transformer 901 and the capacitor 1201 resonance is generated at the frequency of the alternating-current signal generator 703 (or the frequency of the alternating-current power source for driving the magnetoresistive sensor parts 105 ).
  • the amplification factor is improved to be equal to or more than the winding ratio of the step-up transformer 901 (the ratio in number of turns between the primary winding and secondary winding).
  • the step-up transformers 901 explained in embodiments 4 to 6 are effective for reducing noise of the preamplifier 103 , however, it may be possible that problems such that the size (several centimeters) of the step-up transformer 901 is larger, the phase adjustment is more complicated, and the preamplifier 103 is more likely to oscillate. Accordingly, in embodiment 7 of the invention, a configuration of reducing the noise of the preamplifier 103 without using the step-up transformer 901 will be explained.
  • FIG. 13 is a circuit diagram of an MR sensor 100 according to the embodiment 7.
  • the MR sensor 100 in the embodiment 7 includes additional positive feedback (hereinafter, abbreviated as APF) circuits in addition to the configuration explained in embodiment 3.
  • the APR circuit has an APF resistor 1301 and an APF coil 1302 .
  • One APF coil 1302 is provided for each of the magnetoresistive sensor parts 105 (APF coils 1302 - 1 to 1302 - 4 in FIG. 13 ).
  • the APF coil 1302 generates a magnetic field applied to the magnetoresistive elements 101 .
  • the APF resistors 1301 is provided for each of the APF coils 1302 and series-connected to each of the APF coils 1302 .
  • the APF coils 1302 are magnetically coupled to the magnetoresistive sensor parts 105 and feed back the outputs of the magnetoresistive sensor parts 105 as the magnetic fields applied to the magnetoresistive elements 101 to the magnetoresistive elements 101 via the APF resistors 1301 .
  • the APF circuits are provided, and thereby, the magnetic field-voltage conversion efficiency of the magnetoresistive sensor parts 105 is raised and the noise of the preamplifier 103 may be effectively reduced. Only one APF resistor 1301 may be provided in common among the respective APF coils 1302 .
  • the APF resistor 1301 generates thermal noise and is necessary to have a sufficiently lower value than the resistance between both ends of the magnetoresistive sensor part 105 .
  • the resistance value of the APF resistor 1301 is smaller (e.g., about 10 ⁇ )
  • a configuration that the inductance of the APF coil 1302 is made larger so that the output of the magnetoresistive sensor part 105 may not be short-circuited should be formed, and therefore, it is necessary to make the impedance of the APF coil 1302 higher at the frequency of the alternating-current signal generator 703 . It is necessary to make the impedance of the APF coil 1302 at least larger than the resistance between both ends of the magnetoresistive sensor part 105 .
  • the APF circuits that feed back the outputs of the magnetoresistive sensor parts 105 as the magnetic fields applied to the magnetoresistive elements 101 to the magnetoresistive elements 101 is provided, and thereby, the noise of the preamplifier 103 may be substantially reduced without the step-up transformer 901 . Thereby, the equal effect to that of the step-up transformer 901 may be exhibited by the simpler and smaller circuit configuration.
  • FIG. 14 is a circuit diagram of an MR sensor 100 according to embodiment 8 of the invention.
  • the MR sensor 100 in the embodiment 8 has a configuration using both the feedback circuit explained in embodiments 5 and 6 and the APF circuits explained in embodiment 7.
  • the APF coils 1302 also serve as the feedback coils 1102
  • the APF resistors 1301 also serve as the feedback resistors 1101 , and thereby, this is realized. Note that it is necessary to connect the feedback circuits to both the outputs of the magnetoresistive sensor parts 105 and the output of the preamplifier 103 .
  • the APF coils 1302 may not serve as the feedback circuits 1102 , but the coils may be individually provided. The same applies to the APF resistors 1301 and the feedback resistors 1101 .
  • the APF circuits and the feedback circuits are provided within the same drive circuit, and thereby, the system noise may be reduced by the simpler circuit configuration, and further, the influences of the temperature differences depending on the positions of the magnetoresistive sensor parts 105 and the temperature of the measuring object may be suppressed.
  • the system noise maybe reduced using the configurations of the MR sensors 100 explained in embodiments 1 to 8 and the sensitivity that enables measurement of the biomagnetic field may be obtained.
  • the MR sensor 100 having the higher sensitivity detects extraneous interfering magnetic fields generated from automobiles, electric railcars, etc. more easily, and it may be harder to detect only the biomagnetic field components.
  • a configuration of a gradiometer that employs the MR sensors 100 explained in embodiments 1 to 8 are employed, and may efficiently reduce the interfering magnetic fields and measure the biomagnetic field with high sensitivity will be explained.
  • FIG. 15 shows a configuration of a gradiometer 1500 according to the embodiment 9.
  • the gradiometer 1500 includes sensor units 1501 and 1502 and a preamplifier 1503 .
  • Each of the sensor units 1501 and 1502 is formed by parallel connection of a plurality of the MR sensors 100 explained in some of the embodiments 1 to 8.
  • the configuration in which the MR sensors 100 - 1 to 100 - 4 and 100 - 5 to 100 - 8 are parallel-connected is exemplified, however, the number of the MR sensors 100 is not limited to that.
  • the preamplifier 1503 amplifies the difference between the respective outputs of the sensor units 1501 and 1502 , and outputs it from an output terminal 1504 .
  • the sensor units 1501 and 1502 are provided in spatially different locations.
  • the respective outputs of the sensor units in the two locations are amplified by the preamplifier 1503 , and thereby, the number of magnetoresistive sensor parts 105 is doubled and the system noise generated from the resistance of the magnetoresistive sensor parts 105 may be reduced to one 2 1/2 th.
  • a direct-current power source 102 - 1 contained in the sensor unit 1501 and a direct-current power source 102 - 2 contained in the sensor unit 1502 are formed to have opposite polarity to each other. Thereby, the measurement magnetic field directions of the respective sensor units are opposite, and a magnetic sensor that measures the differential magnetic field, i.e., a gradiometer may be formed.
  • the configuration with the two sensor units is exemplified, however, the number of sensor units is not limited to that.
  • an active shield with one sensor unit provided farther from the measuring object that feeds back the measurement result to a plurality of sensor units for biomagnetic field detection to cancel the interfering magnetic fields may be formed.
  • the invention is not limited to the above described embodiments, but includes various modified examples.
  • the above described embodiments are explained in detail for clear explanation of the invention, but not necessarily limited to those including all of the explained configurations.
  • part of the configuration of the embodiment may be replaced by the configuration of the other embodiment.
  • the configuration of the embodiment may be added to the configuration of the other embodiment.
  • addition, deletion, and replacement may be performed by other configurations.
  • 100 MR sensor, 101 : magnetoresistive element, 102 : direct-current power source, 103 : preamplifier, 104 : output terminal, 105 : magnetoresistive sensor part, 401 : substrate, 402 : connector part, 501 : amplifier, 701 : set/reset circuit, 702 : lock-in amplifier, 703 : alternating-current signal generator, 704 : reference signal, 901 : step-up transformer, 1101 : feedback resistor, 1102 : feedback coil, 1201 : capacitor, 1301 : APF resistor, 1302 : APF coil, 1500 : gradiometer, 1501 and 1502 : sensor units, 1503 : preamplifier, 1504 : output terminal.

Landscapes

  • Physics & Mathematics (AREA)
  • Condensed Matter Physics & Semiconductors (AREA)
  • General Physics & Mathematics (AREA)
  • Health & Medical Sciences (AREA)
  • Life Sciences & Earth Sciences (AREA)
  • Nuclear Medicine, Radiotherapy & Molecular Imaging (AREA)
  • Engineering & Computer Science (AREA)
  • Medical Informatics (AREA)
  • Biophysics (AREA)
  • Pathology (AREA)
  • High Energy & Nuclear Physics (AREA)
  • Biomedical Technology (AREA)
  • Heart & Thoracic Surgery (AREA)
  • Radiology & Medical Imaging (AREA)
  • Molecular Biology (AREA)
  • Surgery (AREA)
  • Animal Behavior & Ethology (AREA)
  • General Health & Medical Sciences (AREA)
  • Public Health (AREA)
  • Veterinary Medicine (AREA)
  • Measuring Magnetic Variables (AREA)
  • Measurement And Recording Of Electrical Phenomena And Electrical Characteristics Of The Living Body (AREA)
US14/424,045 2012-08-31 2012-08-31 Magnetoresistive sensor and gradiometer Abandoned US20150212166A1 (en)

Applications Claiming Priority (1)

Application Number Priority Date Filing Date Title
PCT/JP2012/072127 WO2014033904A1 (ja) 2012-08-31 2012-08-31 磁気抵抗センサ、グラジオメータ

Related Parent Applications (1)

Application Number Title Priority Date Filing Date
PCT/JP2012/072127 A-371-Of-International WO2014033904A1 (ja) 2012-08-31 2012-08-31 磁気抵抗センサ、グラジオメータ

Related Child Applications (1)

Application Number Title Priority Date Filing Date
US15/408,863 Division US10247789B2 (en) 2012-08-31 2017-01-18 Magnetoresistive sensor and gradiometer

Publications (1)

Publication Number Publication Date
US20150212166A1 true US20150212166A1 (en) 2015-07-30

Family

ID=50182752

Family Applications (2)

Application Number Title Priority Date Filing Date
US14/424,045 Abandoned US20150212166A1 (en) 2012-08-31 2012-08-31 Magnetoresistive sensor and gradiometer
US15/408,863 Active 2033-01-21 US10247789B2 (en) 2012-08-31 2017-01-18 Magnetoresistive sensor and gradiometer

Family Applications After (1)

Application Number Title Priority Date Filing Date
US15/408,863 Active 2033-01-21 US10247789B2 (en) 2012-08-31 2017-01-18 Magnetoresistive sensor and gradiometer

Country Status (6)

Country Link
US (2) US20150212166A1 (ko)
JP (1) JP5897719B2 (ko)
KR (1) KR101654662B1 (ko)
CN (1) CN104603628B (ko)
DE (1) DE112012006859B4 (ko)
WO (1) WO2014033904A1 (ko)

Cited By (7)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN105301667A (zh) * 2015-10-14 2016-02-03 中国兵器工业集团第二一四研究所苏州研发中心 一种自校准地磁传感器电路
US20190025346A1 (en) * 2017-07-19 2019-01-24 Allegro Microsystems, Llc Systems and methods for closed loop current sensing
US10615887B1 (en) * 2018-09-24 2020-04-07 Seagate Technology Llc Mitigation of noise generated by random excitation of asymmetric oscillation modes
US10925502B2 (en) * 2018-11-20 2021-02-23 Genetesis, Inc. Systems, devices, software, and methods for diagnosis of cardiac ischemia and coronary artery disease
US10928463B2 (en) * 2014-05-15 2021-02-23 Everspin Technologies, Inc. Bipolar chopping for 1/f noise and offset reduction in magnetic field sensors
US20210141116A1 (en) * 2019-11-13 2021-05-13 MAGO technology Co., Ltd. Detector for small metal object including geomagnetic sensors
US11927646B2 (en) 2018-12-26 2024-03-12 Asahi Kasei Microdevices Corporation Magnetic field measuring apparatus

Families Citing this family (11)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
KR101654662B1 (ko) * 2012-08-31 2016-09-07 가부시끼가이샤 히다치 세이사꾸쇼 자기 저항 센서, 그레디오미터
US9632150B2 (en) * 2015-04-27 2017-04-25 Everspin Technologies, Inc. Magnetic field sensor with increased field range
JP6471113B2 (ja) * 2016-03-03 2019-02-13 株式会社日立ハイテクノロジーズ 磁気抵抗センサ、磁気センサプローブ
FR3067125B1 (fr) * 2017-06-02 2019-07-12 Commissariat A L'energie Atomique Et Aux Energies Alternatives Systeme et procede de suppression du bruit basse frequence de capteurs magneto-resistifs
FR3067116B1 (fr) * 2017-06-02 2019-07-12 Commissariat A L'energie Atomique Et Aux Energies Alternatives Systeme et procede de suppression du bruit basse frequence de capteurs magneto-resistifs a magnetoresistence tunnel
CN108414951B (zh) * 2018-03-13 2023-06-30 武汉嘉晨电子技术有限公司 周期性调制磁传感器灵敏度降低器件噪声的方法及装置
WO2020040168A1 (ja) * 2018-08-22 2020-02-27 旭化成エレクトロニクス株式会社 磁場計測装置、磁場計測方法、磁場計測プログラム
EP3882646A1 (en) 2020-03-18 2021-09-22 TE Connectivity Germany GmbH Integrated magnetometer and method of detecting a magnetic field
CN112577531B (zh) * 2020-11-05 2022-01-21 北京麦格纳材科技有限公司 一种磁传感器芯片抗电磁干扰结构及其制备方法
CN115267290A (zh) * 2022-07-08 2022-11-01 珠海多创科技有限公司 阵列式电流传感器
CN115327449B (zh) * 2022-07-22 2024-07-09 三峡大学 一种amr矢量磁力梯度仪

Citations (6)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4616281A (en) * 1982-03-10 1986-10-07 Copal Company Limited Displacement detecting apparatus comprising magnetoresistive elements
US6169396B1 (en) * 1997-02-19 2001-01-02 Mitsubishi Denki Kabushiki Kaisha Sensing device for detecting change in an applied magnetic field achieving high accuracy by improved configuration
US6376933B1 (en) * 1999-12-31 2002-04-23 Honeywell International Inc. Magneto-resistive signal isolator
US6433545B1 (en) * 1998-07-29 2002-08-13 Lust Antriebstechnik Gmbh Method for evaluating signals of magnetoresistive sensors with high band width
US20080048809A1 (en) * 2006-07-12 2008-02-28 Tokai Rika Co., Ltd. Non-contact switch
US8410893B2 (en) * 2011-08-09 2013-04-02 Alps Electric Co., Ltd. Magnetic detector and method for manufacturing the same

Family Cites Families (22)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US5378885A (en) * 1991-10-29 1995-01-03 Mars Incorporated Unshielded magnetoresistive head with multiple pairs of sensing elements
JPH0792395B2 (ja) * 1992-12-11 1995-10-09 日本フローセル製造株式会社 センサつき面積式流量計および流量計測方法
US5491475A (en) * 1993-03-19 1996-02-13 Honeywell Inc. Magnetometer vehicle detector
JP3220278B2 (ja) * 1993-04-20 2001-10-22 カヤバ工業株式会社 位置検出装置
DE19625058A1 (de) * 1996-06-22 1998-01-02 Bosch Gmbh Robert Vorrichtung zur Ermittlung einer Drehrate
JP4092733B2 (ja) * 1997-10-07 2008-05-28 ソニー株式会社 磁気記録再生装置
US6542000B1 (en) * 1999-07-30 2003-04-01 Iowa State University Research Foundation, Inc. Nonvolatile programmable logic devices
JP3692961B2 (ja) * 2001-04-13 2005-09-07 ソニー株式会社 磁気記録データ再生装置及び方法
JP2002311064A (ja) * 2001-04-19 2002-10-23 Daito Communication Apparatus Co Ltd 通電検出方法およびその装置
JP2003194598A (ja) * 2001-12-25 2003-07-09 Tokai Rika Co Ltd センサの異常検出方法及びセンサの異常検出装置
US7112793B2 (en) * 2004-01-05 2006-09-26 Laser Technology, Inc. One-chip compass implemented using magnetoresistive (MR) sensor temperature compensation and magnetic cross-term reduction techniques
JP5067650B2 (ja) * 2006-01-06 2012-11-07 日本電気株式会社 半導体記憶装置
JP4953192B2 (ja) 2006-01-20 2012-06-13 レーザーテック株式会社 位置検出装置
JP2008008883A (ja) 2006-06-02 2008-01-17 Denso Corp 磁気センサ及びセンサ
EP1868254B1 (en) * 2006-06-13 2010-03-24 Hitachi Ltd. Magnetoresistance device
US7818890B2 (en) * 2006-11-27 2010-10-26 Nxp B.V. Magnetic field sensor circuit
JP4899877B2 (ja) * 2007-01-15 2012-03-21 三菱電機株式会社 磁界検出装置
JP4194110B2 (ja) * 2007-03-12 2008-12-10 オムロン株式会社 磁気カプラ素子および磁気結合型アイソレータ
IT1402178B1 (it) * 2010-09-09 2013-08-28 St Microelectronics Srl Circuito di lettura a compensazione automatica dell'offset per un sensore di campo magnetico e relativo metodo di lettura a compensazione automatica dell'offset
TWI409488B (zh) * 2011-09-29 2013-09-21 Voltafield Technology Corp 磁阻感測元件與磁阻感測裝置
KR101654662B1 (ko) * 2012-08-31 2016-09-07 가부시끼가이샤 히다치 세이사꾸쇼 자기 저항 센서, 그레디오미터
WO2018145003A1 (en) * 2017-02-06 2018-08-09 Boston Scientific Scimed Inc. Electromagnetic navigation system with magneto-resistive sensors and application-specific integrated circuits

Patent Citations (6)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4616281A (en) * 1982-03-10 1986-10-07 Copal Company Limited Displacement detecting apparatus comprising magnetoresistive elements
US6169396B1 (en) * 1997-02-19 2001-01-02 Mitsubishi Denki Kabushiki Kaisha Sensing device for detecting change in an applied magnetic field achieving high accuracy by improved configuration
US6433545B1 (en) * 1998-07-29 2002-08-13 Lust Antriebstechnik Gmbh Method for evaluating signals of magnetoresistive sensors with high band width
US6376933B1 (en) * 1999-12-31 2002-04-23 Honeywell International Inc. Magneto-resistive signal isolator
US20080048809A1 (en) * 2006-07-12 2008-02-28 Tokai Rika Co., Ltd. Non-contact switch
US8410893B2 (en) * 2011-08-09 2013-04-02 Alps Electric Co., Ltd. Magnetic detector and method for manufacturing the same

Cited By (12)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US10928463B2 (en) * 2014-05-15 2021-02-23 Everspin Technologies, Inc. Bipolar chopping for 1/f noise and offset reduction in magnetic field sensors
US11353520B2 (en) 2014-05-15 2022-06-07 Everspin Technologies, Inc. Bipolar chopping for 1/f noise and offset reduction in magnetic field sensors
US11733317B2 (en) 2014-05-15 2023-08-22 Everspin Technologies, Inc. Bipolar chopping for 1/f noise and offset reduction in magnetic field sensors
CN105301667A (zh) * 2015-10-14 2016-02-03 中国兵器工业集团第二一四研究所苏州研发中心 一种自校准地磁传感器电路
US20190025346A1 (en) * 2017-07-19 2019-01-24 Allegro Microsystems, Llc Systems and methods for closed loop current sensing
US10557873B2 (en) * 2017-07-19 2020-02-11 Allegro Microsystems, Llc Systems and methods for closed loop current sensing
US10615887B1 (en) * 2018-09-24 2020-04-07 Seagate Technology Llc Mitigation of noise generated by random excitation of asymmetric oscillation modes
US10925502B2 (en) * 2018-11-20 2021-02-23 Genetesis, Inc. Systems, devices, software, and methods for diagnosis of cardiac ischemia and coronary artery disease
US11375935B2 (en) 2018-11-20 2022-07-05 Genetesis, Inc. Systems, devices, software, and methods for diagnosis of cardiac ischemia and coronary artery disease
US11903714B2 (en) 2018-11-20 2024-02-20 Genetesis, Inc. Systems, devices, software, and methods for diagnosis of cardiac ischemia and coronary artery disease
US11927646B2 (en) 2018-12-26 2024-03-12 Asahi Kasei Microdevices Corporation Magnetic field measuring apparatus
US20210141116A1 (en) * 2019-11-13 2021-05-13 MAGO technology Co., Ltd. Detector for small metal object including geomagnetic sensors

Also Published As

Publication number Publication date
US20170168123A1 (en) 2017-06-15
KR101654662B1 (ko) 2016-09-07
KR20150036622A (ko) 2015-04-07
CN104603628A (zh) 2015-05-06
DE112012006859B4 (de) 2021-12-30
JP5897719B2 (ja) 2016-03-30
CN104603628B (zh) 2016-12-14
DE112012006859T5 (de) 2015-05-28
WO2014033904A1 (ja) 2014-03-06
US10247789B2 (en) 2019-04-02
JPWO2014033904A1 (ja) 2016-08-08

Similar Documents

Publication Publication Date Title
US10247789B2 (en) Magnetoresistive sensor and gradiometer
EP2682763B1 (en) Magnetic transducer and current transducer for measuring an electrical current
US11199593B2 (en) Magnetic sensor
US10012705B2 (en) Magnetism measurement device
US8847591B2 (en) Current sensor
CN101738587A (zh) 一种微磁传感器
Ouyang et al. Current sensors based on GMR effect for smart grid applications
JP2009210406A (ja) 電流センサ及び電力量計
CN113866477A (zh) 四磁芯六线圈磁调制高精度超大孔径电流检测方法及系统
US20170307663A1 (en) Current detection method, current detection device, signal correction method for current detection device, and signal correction device for current detection device
JP2011112634A (ja) フラックスゲート漏電センサ用のリングコア、該リングコアを備えるリングコアユニット及びフラックスゲート漏電センサ
US20170205447A1 (en) Current sensor
CN108469594B (zh) 一种高精度、闭环式梯度磁阻传感器
CN216013489U (zh) 宽量程闭环式电流传感器
JP2014222163A (ja) 磁界検出装置の検査用回路及びその検査方法
JP2005188947A (ja) 磁気検出装置
EP2388608B1 (en) Fluxgate sensor circuit for measuring the gradient of a magnetic field
Durdaut et al. Low-Frequency Magnetic Noise in Statically-Driven Solenoid for Biasing Magnetic Field Sensors
Vyhnanek et al. Experimental comparison of the low-frequency noise of small-size magnetic sensors
RU2539726C1 (ru) Феррозондовый магнитометр и способ измерения компонент индукции магнитного поля при помощи векторной компенсации
JP2020041869A (ja) 磁気センサ
Li et al. Tunnel magnetoresistive sensor design and applications for current measurement
Dao et al. Design of a high-sensitivity device for detecting weak magnetic fields
Banjevic et al. Open-loop CMOS current transducer with low temperature cross-sensitivity
CN208156173U (zh) 高精度、闭环式梯度磁阻传感器

Legal Events

Date Code Title Description
AS Assignment

Owner name: HITACHI, LTD., JAPAN

Free format text: ASSIGNMENT OF ASSIGNORS INTEREST;ASSIGNORS:KANDORI, AKIHIKO;SEKI, YUSUKE;KAWABATA, RYUZO;REEL/FRAME:035170/0391

Effective date: 20150129

STCB Information on status: application discontinuation

Free format text: ABANDONED -- FAILURE TO RESPOND TO AN OFFICE ACTION