Device for detecting magnetic signals which are generated by a beating heart

Abstract

The invention relates to a device for detecting magnetic signals which are generated by a beating heart (M), comprising: a first assembly (20) of at least two nitrogen-vacancy centre (NV) magnetometer units, wherein the first assembly (20) has a first main extension plane; a second assembly (20) of at least two NV magnetometer units, wherein the second assembly (20) has a second main extension plane; wherein the first main extension plane is not in parallel with the second main extension plane.

Description

[0001] Description

[0002] title

[0003] Device for detecting magnetic signals generated by a beating heart

[0004] The present invention relates to a device for detecting magnetic signals generated by a beating heart

[0005] Background of the invention

[0006] Optically pumped quantum sensors or those based on NV centers in diamond are particularly suitable for measuring very small magnetic field strengths. DE 10 2022 204 526.2 describes a magnetometer that uses optically pumped and optically detected magnetic resonance (ODMR). This method exploits the fact that the energy levels of certain spin states of unpaired electrons split under the influence of an external magnetic field, the so-called Zeeman effect.

[0007] The splitting of energy levels results in altered transitions during relaxation from excited states, which can then be measured, for example, by optical excitation and frequency-dependent detection of the resulting fluorescence radiation or by observing optical properties such as light absorption. The measured optical parameters can then be used to determine the magnetic field strength.

[0008] Disclosure of the invention

[0009] According to the invention, a device for detecting magnetic signals generated by a beating heart is proposed, having the features of claim 1. Advantageous embodiments are the subject of the subclaims and the following description.

[0010] A magnetocardiogram (MCG for short) is the recording and display of the heart's magnetic field, which is generated by the electrophysiological activity of the heart muscle cells. The invention proposes a contactless, passive method for long-term, high-resolution monitoring of the human heart. This is achieved using nitrogen vacancy magnetometers (so-called NV magnetometers) in a geometric arrangement specifically designed for vector gradiometry.

[0011] In detail, a device for detecting magnetic signals generated by a beating heart is now presented, comprising a first arrangement of at least two NV magnetometer units, each having a first main extension plane, and a second arrangement of at least two NV magnetometer units, each having a second main extension plane, wherein the first main extension plane is not parallel to the second main extension plane. Such a device can also be referred to as a magnetocardiograph. This allows for better resolution of different directional components of the magnetic signals. This has technical advantages, since magnetic field lines are always distributed circularly around a flowing current. Thus, the coverage provided by spatially distributed sensors is greatly improved. This expands the possibilities for signal processing, e.g., through integration in particular.This also means that a measurement can continue to take place even when a user is moving.

[0012] To ensure the widest possible coverage, the first main extension plane and the second main extension plane, in one embodiment, enclose an angle of at least 25°, at least 30°, at least 45°, or at least 60°. In one embodiment, the first main extension plane and the second main extension plane enclose an angle of 80°-90°. This allows magnetic signals to be recorded for any rotational position of the heart around a rotation axis, e.g., with a standing or lying user. The main extension plane of an arrangement is, in particular, the plane into which a projection of the arrangement encloses the largest area.

[0013] In one embodiment, the device comprises a third arrangement of at least two NV magnetometer units, each having a third main extension plane, wherein the third main extension plane is neither parallel to the first nor parallel to the second main extension plane. This allows magnetic signals to be detected for any orientation of the heart in space. In one embodiment, an angle selected from at least 25°, at least 30°, at least 45°, at least 60°, or 80°-90° exists between any two of the first, second, and third main extension planes.

[0014] In one embodiment, the device comprises a further arrangement comprising at least one NV magnetometer unit, which serves to detect a background magnetic field. By directly measuring and taking the background magnetic field into account, the magnetic fields of the heart can be measured even more accurately.

[0015] In one embodiment, the first and / or second and / or third and / or further arrangement is embedded in a body selected from a building wall, a building ceiling, a building floor, and a piece of furniture. Existing features, such as adjacent apartment walls or sloping roofs, can be utilized to detect the spatial magnetic field of the heart. For optimal noise suppression or background field detection, however, arrangements can be placed on those sides of the apartment where the highest level of magnetic noise can be detected, such as toward busy streets or power lines.

[0016] A particular advantage of NV sensors is their size, especially of the sensor medium. For this application, the active measurement volume should be small compared to the object being measured (the heart), otherwise the area coverage would result in integration over large portions of the signal, and thus the signal might disappear because the integral is zero. The smaller the active measurement volume compared to the heart, the better the signal detection. NV sensors have a very small active sensor volume. This small size also allows the sensors to be used in a geometric arrangement. In particular, very high-resolution arrangements are possible due to the very small active sensor volume. This also enables easy integration into bodies or objects.

[0017] Diamond NV magnetometers are based on the reading of magnetic resonances from specific defect centers in diamond, particularly nitrogen vacancies (NV), which occur as impurities in the carbon lattice of diamond and can also be deliberately introduced. If the NV center is optically excited in the ground state, for example, by irradiating a pump laser beam with a suitable wavelength (in this case in the green wavelength range, e.g., at 532 nm for off-resonance excitation), the electrons are lifted from the triplet ground state to the excited triplet state and relax, emitting fluorescent light in the red wavelength range at 650 - 800 nm (637 nm = zero phonon line). Since the probability for non-spin-conserving transitions from the spin state increases with the spin quantum number m s =±1 is larger, continuous excitation pumping ensures that the NV centers are mostly in the spin state m s=0 hyperpolarized.

[0018] Between the m s = 0 and m s =±1 spin states in the ground state, there is an energy difference, which in this case is about 2.87 GHz. Therefore, if microwave radiation is irradiated into the diamond in addition to the optical excitation, a dip in the red fluorescence occurs at this resonance frequency of 2.87 GHz, since the spin-polarized electrons are deflected by the microwave field from the m s = 0 in the m s =±1 ground state and from there by the pump light into the m s =±1 excited state. From there, however, mainly non-radiative transitions and weak infrared fluorescence transitions occur via the singlet state, while fluorescence in the red region disappears. If an external magnetic field is present, the so-called Zeeman effect leads to the splitting of the otherwise equal-energy m s=±1 triplet levels into energetically equidistant Zeeman levels. When the fluorescence is plotted against a frequency spectrum of the microwave excitation, two dips are observed in the fluorescence spectrum, the frequency spacing of which is proportional to the magnetic field strength of the external magnetic field. The magnetic field sensitivity is primarily defined by the minimum resolvable frequency shift and can reach 1 pTA / Hz or less. Since the NV center in single-crystal diamond has four possible arrangements in the crystal lattice, the presence of a directed magnetic field causes the NV centers present in the crystal to react with varying degrees to the external magnetic field depending on their position within the crystal. Ideally, this results in four pairs of fluorescence minima appearing in the spectrum, from whose shape and position relative to each other, both the magnetic field strength (magnitude) and the direction of the external magnetic field can be clearly determined.

[0019] To enable vector magnetic field measurements, the device, in one embodiment, comprises a device for generating a substantially homogeneous bias magnetic field in the region of the magnetometer units or their sensor media, wherein the bias magnetic fields of different NV magnetometer units are expediently different. The device can also be integrated into the body. It can be a Helmholtz coil arrangement, with at least the sensor medium being arranged within the Helmholtz coil arrangement. It can also be other devices, such as a simple coil, an elongated coil, permanent magnet solutions such as in a Hallbach array, etc.

[0020] Heart signals have a magnetic signature with an amplitude of (only) 1 to 2-digit picotesla (pT) at a distance of a few centimeters, whereas, for example, the Earth's magnetic field in Central Europe is about 50 pT (microtesla), i.e. a factor of 10 6stronger. However, even such small field strengths can be resolved with high precision over the long term using the proposed technology. For example, magnetic shielding or a gradiometer circuit can be used for this purpose. High-resolution detection of the precise cardiac signal can detect a variety of diseases, such as permanent atrial fibrillation and intermittent ("paroxysmal") atrial fibrillation. This can prevent a heart attack and, subsequently, a stroke (especially after an undetected heart attack). Furthermore, the invention is suitable for the early detection of ST-elevation myocardial infarction, other types of elevation myocardial infarction, pulmonary embolism, AV nodal retrieval tachycardia, ventricular extrasystoles, and even very rare pathogenic diseases such as arrhythmogenic right ventricular tachycardia, which can otherwise only be detected through gene sequencing.

[0021] Only precise resolution of the cardiac signal enables the detection of these pathologies. In the case of highly noisy or poorly resolved signals, the shifts of the heart's various PQRST complexes relative to each other or over time, fluctuations in their amplitude, deformations, or minor disturbances cannot be detected. However, the resolution of these criteria is important, as the aforementioned problems can lead to complex confusion (e.g., interpreting an elevated and shifted T wave as an R wave, which, however, frequently occurs in a "healthy" heart) and false alarms.

[0022] When a gradiometer interconnection of the at least two NV magnetometer units of an arrangement is used, one magnetometer unit is always at a greater distance from the heart (as a relatively weak magnetic field source) than another magnetometer unit. Through the gradiometer interconnection, i.e., essentially (vector) subtraction of the measured value, the magnetic field gradient approximately corresponds to the field emanating from the weak source, while significantly stronger background fields (which are essentially the same in both magnetometer units) are eliminated. This eliminates the need for magnetic shielding, enabling magnetic field measurement in everyday environments. The invention is accordingly particularly suitable for the unshielded measurement of weak magnetic fields. Technical details of gradiometer solutions that can also be used within the scope of the present invention can be found in DE 102022201690.4, and are intended to be included here.

[0023] In one embodiment, the device is configured to detect a magnetic field strength and field direction using each of the NV magnetometer units of the first and / or second and / or third and / or further arrangement. A further advantage of the NV sensor system is the directional or vector information.

[0024] In contrast to other technologies, this is inherent in NV sensors. There is no need to introduce interference through modulation techniques, use less favorable projections, or use multiple separate sensors. Thus, the vector and gradiometric information are stored at exactly the same location (diamond size, i.e., single-digit mm). A3 and below) and not separated by a few cm to many cm like with other technologies. With NV magnetometer units, which can determine not only the field strength but also the direction of the magnetic field, improved suppression of a background field and thus better detection of signals that are heavily overlaid by interference signals is possible. This is based on two mechanisms: firstly, the signal is not as susceptible to tilting of the sensors relative to each other (in a standard gradiometer application, tilting of the 1D magnetometer leads to a different projection of the measuring or interference field) and this can be compensated for, which is particularly relevant for non-rigid installation combined with localization, e.g. in a mattress. Secondly, the interference field can have a different spatial direction than the field to be measured. This facilitates the separation of signal and background.

[0025] In one embodiment, the device comprises a signal processing unit to which the NV magnetometer units of the first and / or second and / or third and / or further arrangement are connected. The device is configured to use the signal processing unit to determine an effective magnetic field strength and / or an effective magnetic field direction as the difference between the magnetic field strength and field direction detected by the at least two NV magnetometer units. Both a wireless and a wired connection between the sensor system and the signal processing unit is provided.

[0026] For this application, a sampling rate higher than the cardiac signal is required to resolve it, especially higher than 50 Hz. A range of 200 Hz to 400 Hz is considered particularly advantageous. Higher is always better for resolution, but increases the sensitivity requirements.

[0027] Further advantages and embodiments of the invention will become apparent from the description and the accompanying drawings.

[0028] The invention is illustrated schematically in the drawing using exemplary embodiments and is described below with reference to the drawing.

[0029] Short description of the drawings

[0030] Figure 1 shows in a schematic block view the essential components of an NV center magnetometer as can be used in the context of the invention.

[0031] Figure 2 shows, in various figures a) to c), each in a schematic block view, possible arrangements of NV magnetometer units of a device for detecting magnetic signals according to one embodiment.

[0032] Figure 3 shows schematically in a side view a user with a device according to an embodiment of the invention.

[0033] Figure 4 schematically shows, in a perspective view, a number of arrangements in a living space, embedded in different bodies, according to embodiments of the invention. Embodiment(s) of the invention

[0034] Figure 1 schematically shows the essential components of an NV center magnetometer. Initially, a diamond 110 with nitrogen vacancies (NV) serves as the sensor medium. The optical excitation of the NV centers can be achieved by a suitable light source 120, such as an LED or a pump laser. For example, a frequency-doubled Nd:YAG laser or a semiconductor laser in the green range of approximately 510-532 nm is suitable, e.g., at 532 nm for off-resonance excitation. Alternatively, LEDs in suitable wavelength ranges can also be used. Depending on the arrangement, the light from the light source 120 can be irradiated into the diamond 110 via suitable optical elements 122, such as mirrors, beam splitters, focusing optics such as lenses, and optionally via fiber optic elements.In addition, the excitation light can be emitted continuously or in pulsed form by the laser, so that, for example, time windows are kept free for interference-free fluorescence light measurement.

[0035] Furthermore, the magnetometer can comprise a microwave source 150 capable of generating an electromagnetic field in the sensor medium over a bandwidth covering the desired resonance frequency, i.e., in the region of the NV centers of the diamond 110. A microwave resonator structure can be used to homogeneously distribute the generated microwaves across the volume of the measurement area in the diamond. The resonator structure or the microwave source 150 is preferably tuned to the frequency of the electron spin resonances. To enable vector magnetometry, an additional static bias magnetic field 140 is generated. This makes the measurement intrinsically vectorial. Various spatial directions in the crystal structure are used for this purpose. A Helmholtz coil, for example, is suitable for generating such a magnetic field 140, in which a substantially homogeneous magnetic field can be generated in a limited area using a pair of coils.

[0036] The resulting fluorescent light 112 from the diamond 110 can in turn be guided via suitable optical elements 134, such as optical filters, beam splitters, lenses, and / or fiber optic elements, to a first photodetector 130, which is sensitive at least in the range of the fluorescence wavelength. The first photodetector 130 can also be arranged directly on the diamond 110. A second photodetector 132 is arranged such that it can detect at least a portion of the excitation light from the light source 120, which can be coupled out, for example, by a beam splitter, a filter, or a partially transparent element. This detector signal 132 of the excitation light can be used as a reference signal, for example, to eliminate background signals and to highlight the resonance signal of interest by modulating the excitation light using a lock-in amplifier.Additionally or alternatively, this reference signal can be used to account for fluctuations in the excitation light. Appropriate circuits 160, such as a preamplifier, a logarithmic amplifier, a lock-in amplifier, signal filters, or others, are provided to receive the signals from the first and second photodetectors and preprocess the signals appropriately for further evaluation. Finally, the preprocessed fluorescence signal can be evaluated by a signal processing unit 170, e.g., using a suitable microcontroller or processor, to obtain the desired parameters of the detected magnetic field from the signal, in particular the magnetic field strength and the direction of the magnetic field.

[0037] It is understood that such a device may also include additional units not shown, such as communication units or interfaces for outputting the measurement results. Such a device may also advantageously be integrated into an ASIC or FPGA.

[0038] In order to be usable in an everyday environment, magnetic fields that do not originate from desired weak sources should be eliminated from the measurement as far as possible, especially the Earth's magnetic field in the range of 10' 5 Tesla (a few microtesla). In contrast, cardiac magnetic fields range from 10 to 100 times 10' 12 Tesla (Picotesla).

[0039] The elimination of background magnetic fields can be achieved by shielding or by a gradiometer arrangement during magnetic field measurement according to exemplary embodiments. Gradiometers are generally sensor units capable of detecting not only the field strength but also the field gradient.

[0040] For this purpose, at least two individual magnetometer units arranged at spatially different locations can be used. As an example, a sensor unit using two or more NV center magnetometers in a gradiometer arrangement is described below in conjunction with Figure 2.

[0041] Figure 2 shows, in various figures a) to c), possible geometric arrangements of NV magnetometer units of a device for detecting magnetic signals according to one embodiment. Figure a) shows, in a side view, an arrangement of at least two NV magnetometer units S1, ..., Sn in any arrangement to one another in a plane (perpendicular to the plane of the drawing, ie only the first row is visible). The main extension plane is therefore perpendicular to the plane of the drawing. Figure b) shows, in a side view, two NV magnetometer units S1, S2, whose sensor media are sections of the same diamond crystal 110. Figure c) shows, in a side view, a number (n times m) of NV magnetometer units S11, S21, ..., Sn1, S12, S22, ..., Sn2, S1m, ..., Snm in an arrangement parallel to the plane of the drawing. The main extension plane therefore lies in the plane of the drawing.

[0042] Furthermore, M denotes a signal source, here a heart, and O denotes an optional surface (in particular body skin) which limits the accessibility to or reachability of the magnetic field source M.

[0043] In embodiments of the invention, more than two NV magnetometer units can form a gradiometer (but at least two). With each additional NV magnetometer unit, the background field can be better determined, and the location and strength of the exciter can be better separated from the background. In other embodiments of the invention, two NV magnetometer units can also form a gradiometer, in which case—depending on the number of NV magnetometer units—a total of several gradiometers are formed and record the signal of interest. From this, an effective measurement signal can then be formed, in particular by the signal processing unit, for example by averaging, summation, etc.

[0044] A distance d between two NV magnetometer units S1, S2, ... or more precisely their sensor media corresponds to the distance between the locations where simultaneous magnetic field measurements are performed. As long as the distance between the measurement locations is relatively small, it can be assumed that the strength of an additional background magnetic field B env is approximately the same magnitude at both locations. In contrast, the weak magnetic field B of interest will decrease significantly with increasing distance from the magnetic field source M. Furthermore, the different orientation of the magnetic field of the pathogen (e.g., heart) allows for a clear separation from the background field, even at short distances.

[0045] By placing two NV magnetometer units at different distances and angles from the source or the heart, the background field can be eliminated or determined using vector arithmetic, thus determining the small magnetic field of interest and characterizing its source (location and orientation). This can be further improved by placing a distant magnetometer unit or another unit far enough away that the weak magnetic field of interest has dropped below the detection threshold. With such a configuration, local changes in the background field can be compensated for by the at least two nearby magnetometer units.For this purpose, for example, two NV magnetometer units can be arranged one above the other in an axial gradiometer configuration, so that in each case an NV magnetometer unit of a first layer forms a gradiometer with an underlying NV magnetometer unit of a second, underlying layer.

[0046] Figures 3 and 4 schematically illustrate possible embodiments of the invention and are described comprehensively below. Identical elements are provided with the same reference numerals and will not be described repeatedly.

[0047] In each case, a device for detecting magnetic signals is shown, which has at least two arrangements 20, in turn comprising at least two NV magnetometer units, each having a main plane of extension. The device serves to detect magnetic signals generated by a beating heart (M), but can in principle detect all magnetic signals, in particular biosignals, i.e. those emanating from living beings, e.g. signals from a brain (M). For illustration, the figures each have a coordinate system in the top left, wherein the drawing plane represents the xz plane and the y axis extends into the drawing plane. The device further comprises a signal processing unit (not shown), to which the NV magnetometer units of the arrangements 20 are connected in order to determine an effective magnetic field strength and / or field direction.Furthermore, a communication unit (not shown) can be provided to connect the device to other devices such as a PC, tablet PC, or smartphone for input / output and operation. The communication unit can, for example, have wired and / or wireless interfaces. The signal processing unit and the communication unit can also be integrated into the body or arranged externally, e.g., as a stand-alone device, in a control cabinet, etc.

[0048] Figure 3 shows a mattress 1 and a wall 2 as a body; Figure 4 shows a mattress 1 in a bed, a wall 2, and a sloping roof 3, each of which has an arrangement 20 embedded in it. In addition to the examples mentioned, embedding in any furnishings, such as furniture, pictures, lamps, wallpaper, etc., is also contemplated.

[0049] For recording in the frontal plane of a user, a mattress 1, a mattress topper, a bed, or a slatted frame for embedding an arrangement is suitable. For recording the vertical component, a headboard of a bed, a wall 2, a ceiling, or a sloping roof 3 is suitable.

[0050] Numerous sources of ambient magnetic noise (background field) are located outside of private living areas and are therefore inaccessible to reduction. Exterior and interior walls are suitable for their detection and calculation, especially if they are subject to broadband magnetic noise fields. Synchronized recording allows the signals from different arrangements to be calculated and ambient noise signals close to the heart to be reduced.

Claims

Claims 1. Device for detecting magnetic signals generated by a beating heart (M), comprising a first arrangement (20) of at least two nitrogen vacancy center, NV, magnetometer units (S1, S2, ..., Sn; S11, S21, ..., Sn1, S12, S22, ..., Sn2, S1 m, ... Snm), the first arrangement (20) having a first main extension plane, a second arrangement (20) of at least two NV magnetometer units (S1, S2, ..., Sn; S11, S21, ..., Sn1, S12, S22, ..., Sn2, S1 m, ... Snm), the second arrangement (20) having a second main extension plane, the first main extension plane not being parallel to the second main extension plane.

2. Device according to claim 1, wherein the first main extension plane and the second main extension plane enclose an angle of at least 25°, at least 30°, at least 45° or at least 60°.

3. Device according to claim 2, wherein the first main extension plane and the second main extension plane enclose an angle of 80°-90°.

4. Device according to one of the preceding claims, comprising a third arrangement (20) of at least two NV magnetometer units (S1, S2, ..., Sn; S11, S21, ..., Sn1, S12, S22, ..., Sn2, S1m, ... Snm), wherein the third arrangement (20) has a third main extension plane, wherein the third main extension plane is not parallel to the first and not parallel to the second main extension plane.

5. Device according to claim 4, wherein the third main extension plane and the first and / or second main extension plane form an angle selected from at least 25°, at least 30°, at least 45°, at least 60° or from 80°-90°.

6. Device according to one of the preceding claims, comprising a further arrangement (20) comprising at least one NV magnetometer unit (S1, S2, ..., Sn; S11, S21, ..., Sn1, S12, S22, ..., Sn2, S1m, ... Snm), which serves to detect a background magnetic field.

7. Device according to one of the preceding claims, wherein the first and / or second and / or third and / or further arrangement (20) is embedded in a body selected from a building wall, a building ceiling, a building floor and a piece of furniture.

8. Device according to one of the preceding claims, which is designed to detect a magnetic field strength and field direction by means of each of the NV magnetometer units (S1, S2, ..., Sn; S11, S21, ..., Sn1, S12, S22, ..., Sn2, S1 m, ... Snm) of the first and / or second and / or third and / or further arrangement (20).

9. Device according to claim 8, with a signal processing unit (170) to which the NV magnetometer units (S1, S2, ..., Sn; S11, S21, ..., Sn1, S12, S22, ..., Sn2, S1 m, ... Snm) of the first and / or second and / or third and / or further arrangement (20) are connected, wherein the device is set up to determine, by means of the signal processing unit (170), an effective magnetic field strength and / or field direction as the difference between magnetic field strengths and field directions detected by means of the NV magnetometer units (S1, S2, ..., Sn; S11, S21, ..., Sn1, S12, S22, ..., Sn2, S1 m, ... Snm).

10. Device according to one of the preceding claims, wherein the arrangement (20) is a two-dimensional arrangement (20) in which the NV magnetometer units (S1, S2, ..., Sn; S11, S21, ..., Sn1, S12, S22, ..., Sn2, S1 m, ... Snm) of the first and / or second and / or third and / or further arrangement (20) are arranged in the respective main extension plane.

11. Device according to one of the preceding claims, wherein the NV magnetometer units (S1, S2, Sn; S11, S21, Sn1, S12, S22, Sn2, S1m, ... Snm) of the first and / or second and / or third arrangement comprise at least four NV magnetometer units and wherein the arrangement (20) is a three-dimensional arrangement (20) in which at least one of the at least four NV magnetometer units is not arranged in the respective main extension plane in which at least three other of the at least four NV magnetometer units are arranged.

12. Device according to one of the preceding claims, wherein each of the NV magnetometer units (S1, S2, ..., Sn; S11, S21, ..., Sn1, S12, S22, ..., Sn2, S1m, ... Snm) of the first and / or second and / or third and / or further arrangement (20) has a diamond crystal or a section of a diamond crystal with nitrogen vacancy centers as the sensor medium (110), wherein the device is set up to detect a magnetic field strength and / or field direction by reading out a spin resonance in the sensor medium (110) that is dependent on the magnetic field strength.

13. The device according to claim 12, further comprising at least one excitation light source (120) for radiating light (124) into the sensor medium (110), at least one microwave source (150) for generating a resonant field in the sensor medium, and at least one photodetector (130) for detecting resonance-dependent fluorescent light (112) from the sensor medium (110).

14. Device according to claim 13, wherein the NV magnetometer units (S1, S2, ..., Sn; S11, S21, ..., Sn1, S12, S22, ..., Sn2, S1 m, ... Snm) of an arrangement (20) are assigned the same excitation light source (120) and / or the same microwave source (140). Device according to one of claims 12 to 14, wherein the sensor medium is provided by at least two NV magnetometer units (S1, S2, Sn; S11, S21, Sn1, S12, S22, Sn2, S1m, ... Snm) of an array (20) each comprise a portion of the same diamond crystal (110). Device according to one of claims 12 to 15, wherein the distance (d) between the sensor media (110) of the at least two NV magnetometer units (S1, S2, ..., Sn; S11, S21, ..., Sn1, S12, S22, ..., Sn2, S1m, ... Snm) of an array (20) is between 1 and 30 millimeters, preferably between 5 and 20 millimeters.

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