DE102020201565A1 - Method for capturing a magnetic signature - Google Patents

Abstract

Method for detecting a magnetic signature of an object in road traffic with a measuring device which has a sensor unit and an evaluation unit, the sensor unit being a component which has a crystal lattice (10) in which at least one defect is provided which has a fluorescent effect, and a photodetector which is set up to detect the radiation caused by fluorescence in the module and to generate a signal that represents the radiation detected by the photodetector, the evaluation unit evaluates the signal generated by the photodetector in order to establish a spatial association of the object whose magnetic signature is being detected.

Description

The invention relates to a method for detecting a magnetic signature of an object in road traffic and a measuring device for performing the method.

State of the art

The method described is used in particular in the context of a location determination. A location determination is understood to mean the determination of the location in relation to a defined fixed point. In many cases, the determination of one's own location is referred to as location determination. The determination of the location or position of a distant object is often referred to as location. Location determination is understood here to mean both the determination of one's own location and the determination of the location of a distant object. Such a position determination is particularly important in the case of autonomously driving vehicles.

Today's approaches to automated or autonomous driving combine different sensor data in order to determine the current position of a moving object, for example a passenger car. The data from GPS, rader, lidar, camera and inertial sensors are connected to one another, which in the broader sense corresponds to dead reckoning.

The pamphlet DE 10 2015 202 782 A1 describes a method for operating a sensor device which is used to detect an object. A magnetic field sensor with which a parked or a moving vehicle can be detected is used as the environment sensor.

An example of a magnetic field sensor is a magnetometer. This is a sensory device for measuring magnetic flux densities. Magnetic flux densities are measured in Tesla (T) units. Common magnetometers are, for example, Hall sensors, Förster probes, proton magnetometers, Kerr magnetometers and Farady magnetometers.

In addition to the magnetometers mentioned, the use of diamonds is also known, in the lattice of which there are defects or flaws which show a detectable behavior as a function of an applied magnetic field. It is known to use a negatively charged nitrogen vacancy center (NV center) in a diamond for highly sensitive measurements of magnetic fields, electrical fields, mechanical stresses and temperatures. It will be based on this 1 referenced.

The pamphlet DE 10 2014 219 550 A1 describes a combination sensor for measuring a magnetic field, which comprises a sensitive component with diamond structures that have nitrogen defects. The sensitive component can be excited with radiation in the visible range.

• - ultrahohe Empfindlichkeiten (1 pT/VHz),
• - Vektormagnetometrie, d. h. eine Richtungsbestimmung des Magnetfeldes ist möglich,
• - hoher Messbereich (> 1 Tesla),
• - Linearität (Zeemaneffekt),
• - keine Degradation, da die Messung auf quantenmechanischen Zuständen beruht, ähnlich wie beim Wasserstoffatom, bei dem die Rydbergkonstante eine fixe Energie ist, die für alle Atome eine ortsunabhängige und zeitunabhängige Konstante ist,
• - es ist möglich, externe Magnetfelder vektoriell anhand der im Diamant vorhandenen vier möglichen Raumrichtungen der NV-Achsen zu bestimmen.

The quantum technologies used in such arrangements offer decisive advantages over classic sensor principles, which underline the disruptive potential of quantum technology. The following concrete advantages exist with the nitrogen imperfections:

• - ultra-high sensitivities (1 pT / VHz),
• - vector magnetometry, i.e. a directional determination of the magnetic field is possible,
• - high measuring range (> 1 Tesla),
• - linearity (Zeeman effect),
• - no degradation, since the measurement is based on quantum mechanical states, similar to the hydrogen atom, in which the Rydberg constant is a fixed energy that is a location-independent and time-independent constant for all atoms,
• - It is possible to determine external magnetic fields vectorially based on the four possible spatial directions of the NV axes present in the diamond.

To read a sensor based on NV centers, the magnetic resonance of the triplet of the ground state is optically detected, see ³ A state in 1 (ODMR, optically detected magnetic resonance). To do this, the NV center must be stimulated with a green light. It will do this on 2 referenced. The red-shifted fluorescent light, see 2 , shows with additional irradiation of an electromagnetic alternating field (microwave) a characteristic dip in the energetic position of the electron spin resonance, see here 3 . The location is due to the Zeeman effect, see 4th , linearly dependent on the magnetic field, see 3 . This enables a highly sensitive magnetic field sensor to be constructed.

Methods are also known in which NV centers can be read out electrically directly. The excitation conditions, however, are the same.

It must be taken into account that all the methods used do not use the fixed magnetic signature of objects that are present in road traffic, e.g. street signs, tubular posts, etc. It should also be noted that dynamic events, such as the erection of construction sites, have not yet been captured by a magnetic signature of the environment.

Disclosure of the invention

Against this background, a method according to claim 1 and a measuring device according to claim 8 are presented. Embodiments emerge from the dependent claims and from the description.

The presented method is used to detect a magnetic signature of an object in road traffic with a measuring device which has a sensor unit and an evaluation unit, the sensor unit being a component which has a crystal lattice in which at least one defect is provided which has a fluorescent effect, and a photodetector, which is configured to detect the radiation caused by fluorescence in the module and to generate a signal that represents the radiation detected by the photodetector. The evaluation unit evaluates the signal generated by the photodetector in order to enable a spatial assignment of the object whose magnetic signature is being detected.

A spatial assignment of the object means, for example, that the location of the object, which is recorded, for example, with the addition of further systems for determining the location, is entered in a map. If this object has already been entered on a map, the position or the location of the vehicle in which the measuring device is located can be determined on the basis of the recorded signature of the object whose location is stored on the map.

Provision can also be made for data to be exchanged with other vehicles. In this way, data or information from other vehicles can be used to determine the location. Such data or information can also be made available to other vehicles. In this way, information can be provided about dynamic events or objects, which in turn can then be taken into account when calculating the route. In addition, data can also be exchanged with a cloud in which data from other vehicles or from a central point is managed.

The presented measuring device is used to carry out the method and is typically provided in a motor vehicle that can be in traffic. This measuring device comprises a sensor unit, which has a module and a photodetector, and an evaluation unit. The module has a crystal lattice in which at least one defect is provided which has a fluorescent effect. Electromagnetic radiation can be coupled into the building block via a first surface section of the building block, causing fluorescence in the building block, which radiation can be decoupled via a second surface section of the building block, which is typically different from the first surface section. The photodetector, in turn, is set up to detect the radiation caused by fluorescence in the module.

In addition, a filter can be provided which is arranged at least in sections between the module and the photodetector and is set up to allow electromagnetic radiation caused by fluorescence, which is coupled out via the second surface section, to pass through. In this way, the influence of stray light can be reduced.

In one embodiment, a diamond is provided as the crystal lattice. Furthermore, the at least one defect can be designed as a nitrogen defect (NV center). In a further embodiment, the sensor unit of the measuring device additionally has at least one microwave source. In this way, a particularly sensitive and precisely measuring measuring device is to be provided.

With the presented method it is achieved in one embodiment, with the aid of highly sensitive magnetometers, in particular with magnetometers that have an NV center, the magnetic signature of stationary magnetic objects that can be found in road traffic, for example, to use for dead reckoning navigation and in almost real time to map. Furthermore, the data recorded in this way can be pattern matched using AI / ML algorithms with existing magnetic cards. The use of artificial intelligence (AI) or machine learning (ML) methods can be used for a pattern comparison of measured data and existing maps. The use of the AI / ML algorithms should in particular be used to correctly interpret measured data, e.g. B. a car parked on the street or on the edge of the road, which also has a magnetic signature, but does not belong to the relevant objects, such as manhole covers, can be recognized by the named objects by AI detection.

With the help of the highly sensitive magnetometer presented here, it is also possible to use the magnetic signature of dynamically occurring events that briefly affect the fixed magnetic signature found in road traffic for dead reckoning and to map them in almost real time. In addition, the data obtained in this way should be combined with alternative Traffic data, such as GPS, can be compared or a peer-to-peer comparison can be carried out more quickly with the road users in the vicinity.

The presented sensor arrangement and the described method thus use a magnetometer which is set up to detect a magnetic signature and consequently a magnetic field.

A magnetic field is a vector field that describes the magnetic influence of electrical charges in relative movements and magnetized materials. Magnetic fields can be caused, for example, by magnetic materials, electrical currents and changes in an electrical field over time.

A magnetic field can be described with different sizes. The magnetic flux density, which is also referred to as magnetic induction, is a physical quantity in electrodynamics that describes the areal density of the magnetic flux that passes perpendicularly through a certain surface element. The magnetic flux density is a directed quantity, i. H. a vector.

wobei µ, die magnetische Permeabilität ist.The magnetic field strength H is another quantity that describes the magnetic field. This is related to the magnetic flux density B via the relationship: $$\text{B.}=\mathrm{\mu }*\text{H}\text{,}$$

where µ is the magnetic permeability.

To detect a magnetic field, it is necessary to record a quantity that describes this magnetic field. For example, a measuring device can be used which detects a magnitude of the magnetic field, such as the magnetic flux density or the magnetic field strength, and assigns a value to the detected magnitude. Such a measuring device typically comprises a sensor unit and an evaluation unit.

The sensor unit is set up to detect the variable which is used to describe the magnetic field and which thus represents this magnetic field. The sensor unit comprises at least one highly sensitive magnetometer, which has a high dynamic range and enables vectorial detection of the magnetic field.

The evaluation unit comprises at least one processing unit which uses, for example, AI / ML algorithms in order to use a pattern comparison with already existing magnetic data and to determine the difference. It also offers an interface to provide the determined data for dead reckoning. Furthermore, an interface can be provided in order to forward the data to a central point, which is used there for mapping the magnetic signature. This can also be done when using a cloud. This interface or a further interface can be set up to carry out a comparison with the local road users. This is known as peer-to-peer.

• Es bietet weitere Sensorgrößen für die Koppelnavigation, die dabei lokal und über längere Zeiträume einzigartig sind, zudem kann es autark betrieben werden, ein kostengünstiger Sensoraufbau ist erforderlich, es besteht ein besonders hohes Miniaturisierungspotential der Sensoreinheit und ein Erfassen von dynamischen Ereignissen der magnetischen Signatur in Echtzeit ist möglich.

The presented method has the following advantages, at least in some of the versions:

• It offers additional sensor sizes for dead reckoning, which are unique locally and over longer periods of time; it can also be operated independently, a cost-effective sensor structure is required, there is a particularly high potential for miniaturization of the sensor unit and the detection of dynamic events of the magnetic signature in real time is possible.

The presented sensor unit and the described method thus make use of the possibility that many objects in road traffic or in the road traffic network, such as pipe posts, road covers, manhole covers, guard rails, etc., are in most cases made of magnetic materials or a high proportion of magnetic materials Have substances. This is, for example, iron, nickel, etc. The consequence of these magnetic substances is that they locally strongly change the magnetic signature of the field to be measured. Therefore, abrupt changes or deviations in the earth's magnetic field occur. With the presented high-resolution vector magnetometer, such as, for example, the NV center in a diamond, which expediently also has a high dynamic range, these deviations can be recorded and used for navigation purposes. A pattern comparison with a previously mapped magnetic map enables a very precise determination of the position of moving objects. In addition, the data obtained can be used for dead reckoning.

Dynamic objects or events, such as B. the erection of construction sites lead to short-term, days, weeks. Months, change of magnetic signature. The measuring or transmitting unit should offer the possibility of capturing this dynamic magnetic signature and forwarding it to a central point or to the local road users. When the magnetic signature is recorded, other sensor variables can also be evaluated.

The presented measuring device and the described method can be used in particular in the field of autonomous driving.

Further advantages and configurations of the invention emerge from the description and the accompanying drawings.

It goes without saying that the features mentioned above and those yet to be explained below can be used not only in the respectively specified combination, but also in other combinations or on their own, without departing from the scope of the present invention.

Figure list

• 1 shows nitrogen vacancies (NV centers) in a diamond.
• 2 shows an absorption and emission spectrum of the NV center.
• 3 shows an optically detected magnetic resonance of a single NV center.
• 4th shows the Zeeman effect within the energy diagram of the negatively charged NV center.
• 5 shows a schematic representation of the structure of a magnetometer.
• 6th shows a possible implementation of the presented method in a flowchart.
• 7th shows a further possible implementation of the presented method in a further flowchart.

Embodiments of the invention

The invention is shown schematically on the basis of embodiments in the drawings and is described in detail below with reference to the drawings.

1 shows on the left a crystal lattice, in this case a diamond, the crystal lattice as a whole with reference number 10 is designated. The crystal lattice 10 includes a number of carbon atoms 12th and an NV center 14th which in turn is a nitrogen atom 16 and a gap or vacancy 18th having. The nitrogen void 14th is aligned along one of the four possible bond directions in the diamond crystal.

wobei ΔT die Abweichung von der Raumtemperatur, β die temperaturbedingte Verschiebung des Zero-Field Splittings mit β ungefähr -74,2 Kilohertz/Kelvin, y_NV das gyromagnetische Verhältnis des NV-Zentrums und B₀ die Feldstärke eines externen Magnetfelds angibt.On the right is the energy level scheme 30th of the negatively charged NV center 14th shown. A basic state ³ A ₂ 32 is a spin triplet with total spin s = 1. The states 34 with magnetic spin quantum number ms = + - 1 are opposite to the state 36 energetically shifted with ms = 0. There is still a state ³ E 38 and an intermediate state 40 shown. With bracket 42 a microwave frequency of 2.87 GHz is illustrated, which corresponds to a splitting energy or zero-filed splitting Dgs. The zero-filed splitting is an intrinsic quantity that is independent of the radiated MW field or the MW frequency. Si is approximately 2.87 GHz and is particularly temperature dependent. The following relationship applies to the determination of the resonance frequency: $$\text{v}\pm \approx {\text{D.}}_{\text{gs}}+\mathrm{\beta \; \ast }\Delta \mathrm{{\rm T}}\pm {\text{y}}_{\text{NV}}\mathrm{\ast }{\text{B.}}_0;$$

where ΔT is the deviation from room temperature, β is the temperature-related shift of the zero-field splitting with β approximately -74.2 kilohertz / Kelvin, y _NV the gyromagnetic ratio of the NV center and B ₀ the field strength of an external magnetic field.

2 shows in a graph 50 the absorption and emission spectrum of the NV center, which is shown in 1 is shown. In the graph 50 is on an abscissa 52 the wavelength [nm] and on a first abscissa 54 the absorption coefficient [cm ^-1 ] and on a second abscissa 56 applied the fluorescence. A first turn 60 shows the absorption spectrum, a second curve 62 shows the emission spectrum. A first arrow 70 indicates NV ⁰ ZPL, a second arrow 72 denotes NV ^- absorption, a third arrow 74 denotes NV ^- fluorescence. Furthermore NV ^- ZPL 76 entered at 637 nm.

3 shows in a graph 100 the optically detectable magnetic resonance (ODMR) of a single NV center for different background magnetic fields. In the graph 100 is on an abscissa 102 the microwave frequency, on a first ordinate 104 the magnetic field B and on a second ordinate 106 applied the fluorescence.

A first turn 110 shows the resonance for B = 0, a second curve 112 shows the resonance at B = 2.8 mT with the negative peaks ω ₁ 114 and ω ₂ 116 , a third curve 120 the resonance for B = 5.8 mT and a fourth curve 122 the response for 8.3 mT.

4th shows the Zeeman effect in the ground state 150 of the NV center. Furthermore are the excited state 152 and the intermediate state 154 registered. A first arrow 160 shows a transition with a high probability or transition rate, a dashed arrow 162 shows a transition with a low probability or transition rate. In a box 170 are a transition 172 without a magnetic field and a transition 174 reproduced with a magnetic field.

5 shows in schematic form components that are required in execution for the ODMR principle (ODMR: Optically Detected Magnetic Resonance) used here. These are: a light source 200 in the green, possibly an optic to direct the beam onto a diamond 202 to lead the diamond 202 having NV centers, a microwave source 204 and matching cables 206 , the microwaves (MW) in the frequency range around the so-called zero-field splitting at around 2.87 gigahertz to the diamond 202 lead a filter 208 , in particular a color filter that only transmits the red-shifted fluorescent light, possibly additional optics, and a photo detector 210 that detects the fluorescence radiation.

6th shows a possible implementation of the presented method in a flowchart. In a first step 250 drives the vehicle in traffic. In a further step 252 a magnetic signature of an object is captured. Then in one step 254 With a further system for determining the location, for example a GPS system, the position of the vehicle and thus the location of the object whose magnetic signature was recorded is determined. This place is in a further step 256 entered in a card. On the basis of this map, in which the location of the object is now entered, the vehicle can determine its position during later journeys, if it typically drives on the same route, when the magnetic signature is recognized, without the need for an additional system for location determination will. In a final step 258 the vehicle then forwards data or information on the object and its signature with position coordinates to a cloud.

7th shows a further embodiment of the method. In a first step 280 drives the vehicle in traffic. In a further step 282 a magnetic signature of an object is captured. The vehicle can now be compared with a map provided in one step 284 check whether the recorded signature is entered. If this is the case, the position of the vehicle can be determined in one step without the need for a further system for determining the location 286 to be determined. If there is no entry in the map, the location of the object can be determined in one step with the aid of a further system for determining the location 288 be entered on the card.

QUOTES INCLUDED IN THE DESCRIPTION

This list of the documents listed by the applicant was generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Patent literature cited

• DE 102015202782 A1 [0004]
• DE 102014219550 A1 [0007]

Claims (12)

Method for detecting a magnetic signature of an object in road traffic with a measuring device which has a sensor unit and an evaluation unit, wherein - The sensor unit has a building block which has a crystal lattice (10) in which at least one defect is provided which has a fluorescent effect, and a photodetector (210) which is set up to detect the radiation caused by fluorescence in the building block and generate a signal representing the radiation detected by the photodetector (210) comprises, - The evaluation unit evaluates the signal generated by the photodetector (210) in order to enable a spatial assignment of the object whose magnetic signature is being detected. Procedure according to Claim 1 which captures the magnetic signature of a dynamic object. Procedure according to Claim 1 or 2 , in which the signal evaluated by the evaluation unit is compared with at least one signal that is provided by other systems for determining the location. Procedure according to Claim 3 , in which an entry of the object whose magnetic signature is detected is made in a card. Method according to one of the Claims 1 until 4th , in which the location of a motor vehicle in road traffic is determined. Method according to one of the Claims 1 until 5 , in which data is exchanged with other vehicles. Method according to one of the Claims 1 until 6th , in which data is exchanged with a cloud. Measuring device with a sensor unit, which has a module and a photodetector (210), and an evaluation unit, the measuring device for performing a method according to one of the Claims 1 until 7th is set up, wherein - the module has a crystal lattice (10) in which at least one defect is provided which has a fluorescent effect, - electromagnetic radiation can be coupled into the module via a first surface section of the module, which causes fluorescence in the module which can be decoupled via a second surface section of the building block, - the photodetector (210) is set up to detect the radiation caused by fluorescence in the building block. Measuring device according to Claim 8 , in which a filter (208) is additionally provided, which is arranged at least in sections between the module and the photodetector (210) and is set up to let through electromagnetic radiation caused by fluorescence, which is to be coupled out via the second surface section. Measuring device according to Claim 8 or 9 , in which a diamond (202) is provided as a crystal lattice (10). Measuring device according to one of the Claims 8 until 10 , in which the at least one defect is designed as a nitrogen defect (NV center) (14). Measuring device according to one of the Claims 8 until 11 which additionally has at least one microwave source (204).

Images