DE102022209436A1 - Device for detecting magnetic signals generated by a beating heart - Google Patents

Abstract

The invention relates to a device for detecting magnetic signals that are generated by a beating heart (M), comprising at least two nitrogen vacancy centers, NV, magnetometer units (S1, S2), which are in a geometric, in particular substantially are arranged in a flat arrangement relative to one another and are connected to a signal processing unit (170, 200), the device being set up to determine a magnetic field strength (R1, R2) and field direction (R1, R2) by means of each of the at least two NV magnetometer units (S1, S2). ) to detect, and by means of the signal processing unit (170, 200) to determine an effective magnetic field strength and field direction from the magnetic field strength and field direction detected by means of the at least two NV magnetometer units (S1, S2).

Description

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

Background of the invention

In order to measure very small magnetic field strengths, optically pumped quantum sensors or quantum sensors based on NV centers in diamond are particularly suitable sensors. In the DE 10 2022 204 526.2 A magnetometer is described that uses optically pumped and optically detected magnetic resonances (ODMR). This takes advantage of 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. The splitting of the energy levels results in changed transitions during relaxation from excited states, which can then be measured, for example, by optical excitation and frequency-dependent detection of the resulting fluorescent radiation or by observing optical properties such as the absorption of light. The magnetic field strength can then be deduced from the measured optical parameters.

Disclosure of the invention

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

A magnetocardiogram (abbreviated MKG) is the recording and display of the heart's magnetic field, which is created by the electrophysiological activity of the heart muscle cells. As part of the invention, a contactless, passive option for long-term monitoring of the human heart with high resolution is presented. This is achieved using nitrogen vacancy magnetometers (so-called NV magnetometers) in a geometric arrangement for vector gradiometry.

In detail, a device for detecting magnetic signals generated by a beating heart is now presented, which has at least two NV magnetometer units, which are arranged in a geometric, in particular essentially flat, arrangement relative to one another and are connected to a signal processing unit , wherein the device is set up to detect a magnetic field strength and field direction by means of each of the at least two NV magnetometer units, and to determine an effective magnetic field strength and field direction from the magnetic field strength and field direction detected by means of the at least two NV magnetometer units by means of the signal processing unit . Both a wireless and wired connection between the sensor system and the signal processing unit is provided. Such a device can also be called a magnetocardiograph.

The effective magnetic field strength and field direction are determined in particular by vector arithmetic. Essentially this means that certain deviations within normal tolerances are unavoidable in practice. However, the distance between two NV magnetometer units in the plane (projected on an x/y plane) should be significantly larger than any difference in height (z-axis), e.g. at least two, five or ten times as much large. By specifically arranging the at least two NV magnetometer units close to the heart, e.g. in a line, at the corners and/or edges of a polygon, on the circumference and possibly on the center of a circle, the number of sensors required can be minimized.

Diamond NV magnetometers are based on reading out the magnetic resonances of special defect centers in diamond, in particular nitrogen vacancies (NV), which occur as impurities in the carbon lattice of diamond and can also be introduced in a targeted manner. 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 converted from the triplet ground state into the excited triplet -State raised and relaxed with emission of fluorescent light in the red wavelength range at 650 - 800 nm (637nm = zero phonon line). Since the probability of non-spin-conserving transitions from the spin state with the spin quantum number m _s =±1 is greater, continuous excitation pumping ensures that the NV centers are largely hyperpolarized in the spin state m _s =0.

There is an energy difference between the m _s = 0 and m _s = ±1 spin states in the ground state, which in this case is around 2.87 GHz. If, in addition to the optical excitation, microwave radiation is irradiated into the diamond, the red fluorescence drops at this resonance frequency of 2.87 GHz, since the spin-polarized electrons move through the microwave field from m _s = 0 to m _s = ±1 -Basic state can be raised and from there excited by the pump light into the m _s =±1 excited state. From there, however, mainly non-radiative transitions and weakly infrared fluorescence transitions occur over the singlet state, while the fluorescence in the red range disappears.

If an external magnetic field is present, the so-called Zeeman effect causes the otherwise equal-energy m _s = ±1 triplet levels to split into energetically equidistant Zeeman levels. When the fluorescence is plotted against a frequency spectrum of the microwave excitation, two dips appear 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 defined primarily by the minimally resolvable frequency shift and can reach up to 1 pT/√Hz or less. Since the NV center in single-crystalline diamond has four ways of arranging itself in the crystal lattice, in the presence of a directed magnetic field, the NV centers present in the crystal react to the external magnetic field with different strengths depending on their location in the crystal. This means that, ideally, four pairs of fluorescence minima can appear in the spectrum, from whose shape and position relative to each other both the magnetic field strength as an amount and the direction of the external magnetic field can be clearly determined. In order to enable vector magnetic field measurements, the device has a device for generating a substantially homogeneous bias magnetic field in the area of the magnetometer units or their sensor media, the bias magnetic fields of different NV magnetometer units expediently being different. This can be a Helmholtz coil arrangement, with at least the sensor medium being arranged within the Helmholtz coil arrangement (each magnetometer unit more conveniently has its own bias field, which improves the field determination). It can also be other devices such as a simple coil, an elongated coil, permanent magnet solutions such as in a Hallbach array, etc.

By using a number of vector magnetometer units in a geometric arrangement and gradiometer circuit, these magnetometer units have a different orientation to the heart's magnetic field. The position and strength of the magnetic field exciter (heart) can be determined by the gradiometer connection, ie essentially vector arithmetic of what is measured. Since the much stronger background field is essentially the same in both magnetometer units (same strength and orientation), it can be eliminated. This eliminates the need for magnetic shielding, making magnetic field measurement possible in everyday environments. Another advantage over classic gradiometer arrangements with one-dimensional magnetometers is the compact design this enables, as no distant reference magnetometer is required. The invention is particularly suitable for unshielded measurement of weak magnetic fields. Technical details of gradiometer solutions that can also be used within the scope of the present invention are in DE 102022201690.4 disclosed, and should be included here.

Heart signals have a magnetic signature at a distance of a few cm with an amplitude of (only) picotesla (pT), whereas, for example, the earth's magnetic field in Central Europe is approx. 50 µT (microtesla), i.e. stronger by a factor of 10 ⁶ . However, even such small field strengths can be resolved with high precision over the long term using the proposed technology.

Through the high-resolution detection of the precise heart signal, a variety of diseases can be detected, such as permanent atrial fibrillation and paroxysmal atrial fibrillation. This can prevent a heart attack and, as a result, a stroke (especially after an undetected heart attack). Furthermore, the invention is suitable for the early detection of an S-T elevation myocardial infarction, other types of elevation myocardial infarction, a pulmonary embolism, an AV nodal renttry tachycardia, ventricular extrasystoles, but also very rare pathogenic diseases such as arrhythmogenic right ventricular tachycardia, which can otherwise only be identified through gene sequencing can be recognized.

A particular advantage of NV sensors is the direction or vector information. In contrast to other technologies, this is intrinsic to NV sensors. This means that there is no need to introduce interference through modulation techniques, use less favorable projections, or use several separate sensors. This means you have the vector and gradiometry information in exactly the same place (diamond size, i.e. single-digit mm^3 and below) and not separated from a few cm to many cm as with other technologies. With NV magnetometer units that not only measure 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 superimposed by interference signals are made possible. This is based on two mechanisms of action: firstly, the signal is not as susceptible to tilting between the sensors (in a standard gradiometer application, tilting the 1D magnetomer leads to a different projection of the measuring or interference field) and this can be compensated for, which is particularly important is 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 makes it easier to separate the signal from the background.

Only precise resolution of the heart signal enables this detection of the clinical pictures. In the case of very noisy or poorly resolved signals, the shifts of the various PQRST complexes of the heart relative to one another or over time, fluctuations in their amplitude, deformations or small disturbances cannot be detected. However, this resolution of these criteria are important factors, as the problems mentioned above can lead to mix-ups of complexes (e.g. interpretation of an elevated and shifted T wave as an R wave, which, however, often occurs in a “healthy” heart) and false alarms.

Another advantage of NV sensors is their size, especially of the sensor medium. For the application, the active measuring volume should be small compared to the object to be measured (heart), otherwise the surface coverage will result in large parts of the signal being integrated and the signal may therefore disappear because the integral is zero. The smaller the active measurement volume compared to the heart, the better the signal detection. NV sensor technology has a very small active sensor volume. This small design also enables 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.

The application requires a sampling rate that is higher than the heart signal in order to resolve it, in particular greater than 50Hz. A range from 200Hz to 400 Hz is considered particularly advantageous. Higher is always better for resolution, but increases the sensitivity requirements.

Further advantages and refinements of the invention result from the description and the accompanying drawing.

The invention is shown schematically in the drawing using exemplary embodiments and is described below with reference to the drawing.

Brief description of the drawings

• 1 shows a schematic block view of the essential components of a NV center magnetometer, as it can be used within the scope of the invention.
• 2 shows in various figures a) to c), each in a schematic block view, possible geometric arrangements of NV magnetometer units of a device for detecting magnetic signals according to one embodiment.
• 3 shows a schematic block view of a measuring principle of NV vector gradiometry, as can be used in an embodiment of the invention.
• 4 shows in various figures a) to c) a top view of possible geometric arrangements of NV magnetometer units in a plane of a device for detecting magnetic signals according to one embodiment.

Embodiment(s) of the invention

1 shows schematically the essential components of a NV center magnetometer. Initially, a diamond 110 with nitrogen vacancies (NV) is present as a 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 semiconductor laser in the green range of around 510-532nm, for example at 532nm, is suitable 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, if necessary, via fiber optic elements. In addition, the excitation light can be irradiated by the laser continuously or in pulses, so that, for example, time windows are kept free for interference-free fluorescent light measurement.

Further, the magnetometer may include a microwave source 150 capable of generating an electromagnetic field across a bandwidth covering the desired resonant frequency in the sensor medium, i.e. in the area of the NV centers of the diamond 110. A microwave resonator structure may can be used to homogeneously distribute the generated microwaves over the volume of the measuring 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. 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 by means of a pair of coils.

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 so that it can detect at least part of the excitation light from the light source 120, which can be coupled out, for example, through 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 in order to eliminate background signals and highlight the resonance signal of interest, for example by modulating the excitation light using a lock-in amplifier. Additionally or alternatively, this reference signal can be used to take fluctuations in the excitation light into account. Corresponding circuits 160 such as a preamplifier, a logarithmic amplifier, a lock-in amplifier, signal filters or others are therefore provided in order to receive the signals from the first and second photodetectors and to preprocess the signals in a suitable manner for further evaluation. Finally, the preprocessed fluorescence signal can be evaluated by a signal processing unit 170, for example with a suitable microcontroller or processor, in order 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. Such a device can also advantageously be integrated into an ASIC or FPGA.

In order to be usable in an everyday environment, magnetic fields that do not come from desired weak sources should be eliminated from the measurement as far as possible, in particular the earth's magnetic field in the range of 10 ^-5 Tesla (a few microteslas). In contrast, cardiac magnetic fields are in the range of 10 ^-12 Tesla (Picotesla).

The elimination of the background magnetic fields can be achieved by a gradiometer arrangement during magnetic field measurement according to exemplary embodiments. Sensor units that are able to record not only the field strength but also the gradient of the field are generally referred to as gradiometers.

For this purpose, at least two individual magnetometer units S1, S2, ..., Sn; S11, S21, ..., Sn1, S12, S22, ..., Sn2, S1m, ..., Snm are used, which are arranged at spatially different locations. As an example, the following is used in conjunction with 2 describes a sensor unit that uses two or more NV center magnetometers in a gradiometer arrangement.

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 a side view of an arrangement of at least two NV magnetometer units S1, S2, ..., Sn in any arrangement relative to one another in a plane (perpendicular to the plane of the drawing; ie only the first row is visible). Figure b) shows a side view of two NV magnetometer units S1, S2, whose sensor media are sections of the same diamond crystal 110. ) shows a side view of a number (n by m) of NV magnetometer units S11, S21, ..., Sn1, S12, S22, ..., Sn2, S1m, ..., Snm in any three-dimensional arrangement. Additional layers (not shown) follow the drawing plane, so that overall a kind of cubic grid is formed. At least one NV magnetometer unit (not shown), which lies, for example, in one of the rear layers, is not arranged in the plane (drawing plane) in which other NV magnetometer units are arranged.

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

In embodiments of the invention, more than two NV magnetometer units can form a gradiometer in total (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 always form a gradiometer, in which case - depending on the number of NV magnetometer units - a total of several gradiometers are formed and detect the signal of interest. An effective measurement signal can then be formed from this, in particular by the signal processing unit, for example by averaging, summation, etc.

A distance d between two NV magnetometer units S1, S2, ... or more precisely their sensor media corresponds to the distance between the locations where magnetic field measurements are carried out at the same time. 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 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 a clear separation from the background field even at small distances.

By arranging two NV magnetometer units at different distances and angles from the source or from the heart, the background field can be eliminated or determined using vector arithmetic and thus the small magnetic field of interest can be determined and its source can be characterized (location and orientation). This can be further improved by a remote magnetometer so far away that the weak magnetic field of interest has fallen below the detection threshold. With such a configuration, local changes in the background field can be compensated for by the at least two nearby magnetometers. 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 a NV magnetometer unit of a first layer forms a gradiometer with an underlying NV magnetometer unit of a second, underlying layer. The background field can also be determined by placing another LV magnetometer unit at a large distance, e.g. at least 1 m, from the two LV magnetometer units.

One concept of the invention is to measure the field vectorially and simultaneously from different positions using several NV magnetometer units. As long as this arrangement is in the vicinity of the signal source M that is to be measured, the field of the signal source is measured in different directions with the individual vector sensors. This distribution of the measured field vectors is characteristic and allows conclusions to be drawn about the source regarding strength, position and orientation. In order to detect weak signals compared to the background, it is possible to assume a homogeneous background field across the geometric arrangement of NV magnetometer units (this is usually assumed here because the distance between the source of the interference and the sensor medium can be assumed to be much larger than that). of the signal to be measured to the sensor medium) to calculate the individual field vectors, since the vector of the interference field can be assumed to be the same and therefore simple vector arithmetic is sufficient to extract the signal vector. If a geometric arrangement is used, inhomogeneities in the background can also be compensated for.

As in 3 shown, the different measuring positions of the NV magnetometer units S1, S2 determine the field vector in different directions. Since the background field Z1 is the same for both NV magnetometer units, this allows a back calculation of the strength and orientation of the source. By measuring the signal/field in different directions (the source's field depends on the position of the individual sensor in relation to the source in terms of amplitude and orientation), noise in the background field can be further suppressed (fluctuations orthogonal to the measurement signal are suppressed). This allows for noise reduction that is superior to the traditional gradiometer approach.

3 shows a schematic block view of a measuring principle of NV vector gradiometry, as can be used in an embodiment of the invention. M1 to Mn are at least one magnetic field component and Z1 to Zn are at least one interference component (e.g. earth's magnetic field), which sta can change over time or table. Since both NV magnetometer units S1 and S2 (expandable to ) measure resulting components R1 to Rn, which contain the interference signal, a signal that is insensitive to the interference components can be determined by suppression. The NV magnetometer unit S1 measures the component R1 consisting of the first disturbance Z1 and the signal M1 at the location of S1 and the NV magnetometer unit S2 measures the component R2 consisting of the first disturbance Z1 and the signal M1 'at the location of S2.

• Gemessen werden zwei vektorwertige Signale R1 und R2. Diese enthalten Signalanteile M1 und M1' sowie Störanteile Z1 und Z2=Z1, welche insbesondere gleich für die Messbereiche sind. Das Gradiometermesssignal ergibt sich dann nach: $$\overrightarrow{S}=\overrightarrow{R1}-\overrightarrow{R2}=\left(\begin{array}{c}{R}_{\mathrm{1,}x}\\ R_{\mathrm{1,}y}\\ R_{\mathrm{1,}z}\end{array}\right)-\left(\begin{array}{c}{R}_{\mathrm{2,}x}\\ R_{\mathrm{2,}y}\\ R_{\mathrm{2,}z}\end{array}\right)=\left(\begin{array}{c}{M}_{\mathrm{1,}x}+Z_{\mathrm{1,}x}\\ M_{\mathrm{1,}y}+Z_{\mathrm{1,}y}\\ M_{\mathrm{1,}z}+Z_{\mathrm{1,}z}\end{array}\right)-\left(\begin{array}{c}M{\text{'}}_{\mathrm{1,}x}+Z_{\mathrm{1,}x}\\ M{\text{'}}_{\mathrm{1,}y}+Z_{\mathrm{1,}y}\\ M{\text{'}}_{\mathrm{1,}z}+Z_{\mathrm{1,}z}\end{array}\right)=\left(\begin{array}{c}{M}_{\mathrm{1,}x}+M{\text{'}}_{\mathrm{1,}x}\\ M_{\mathrm{1,}y}+M{\text{'}}_{\mathrm{1,}y}\\ M_{\mathrm{1,}z}+M{\text{'}}_{\mathrm{1,}z}\end{array}\right)$$
  

An evaluation using the example of two NV magnetometer units S1 and S2 as in 3 shown can proceed as follows:

• Two vector-valued signals R1 and R2 are measured. These contain signal components M1 and M1' as well as interference components Z1 and Z2=Z1, which are in particular the same for the measuring ranges. The gradiometer measurement signal then results from: $$\overrightarrow{S}=\overrightarrow{R1}-\overrightarrow{R2}=\left(\begin{array}{c}{R}_{\mathrm{1,}x}\\ R_{\mathrm{1,}y}\\ R_{\mathrm{1,}\mathrm{e.g}}\end{array}\right)-\left(\begin{array}{c}{R}_{\mathrm{2,}x}\\ R_{\mathrm{2,}y}\\ R_{\mathrm{2,}\mathrm{e.g}}\end{array}\right)=\left(\begin{array}{c}{M}_{\mathrm{1,}x}+Z_{\mathrm{1,}x}\\ M_{\mathrm{1,}y}+Z_{\mathrm{1,}y}\\ M_{\mathrm{1,}\mathrm{e.g}}+Z_{\mathrm{1,}\mathrm{e.g}}\end{array}\right)-\left(\begin{array}{c}M{\text{'}}_{\mathrm{1,}x}+Z_{\mathrm{1,}x}\\ M{\text{'}}_{\mathrm{1,}y}+Z_{\mathrm{1,}y}\\ M{\text{'}}_{\mathrm{1,}\mathrm{e.g}}+Z_{\mathrm{1,}\mathrm{e.g}}\end{array}\right)=\left(\begin{array}{c}{M}_{\mathrm{1,}x}+M{\text{'}}_{\mathrm{1,}x}\\ M_{\mathrm{1,}y}+M{\text{'}}_{\mathrm{1,}y}\\ M_{\mathrm{1,}\mathrm{e.g}}+M{\text{'}}_{\mathrm{1,}\mathrm{e.g}}\end{array}\right)$$
  

As equation (1) describes, the signal no longer contains any interference components as long as they are uniform across the measuring ranges. Furthermore, the measurement signal is vectorial, so it allows, for example, the assignment of the direction (“Where does the signal come from?”), the differentiation of different signals, and the correlation of several signals from different sensors in an arrangement (imaging process).

The result in Equation 1 can be expressed in terms of a magnitude and a direction. This is particularly advantageous if the source is between the magnetometer units and the magnetic field is therefore opposite. By using three or more magnetometer units (geometric arrangement), a system of equations can be set up that allows the individual magnetic fields on the magnetometer units to be determined.

Another advantage is that with conventional gradiometers the difference is measured from two scalar sensors that are connected in series. The performance depends on the fact that a sensor only measures the background field (measured values (scalar) are only subtracted from each other). Furthermore, in this case the difference between the sensors is always smaller than the actual measured value (< M). The approach described here can determine the measurement signal at different angles to the background signal by arranging it at different solid angles (also projected onto a plane). This increases the signal-to-noise ratio and thus the sensitivity (in the symmetrical ideal case, with two sensors, the magnetic field is exactly opposite).

Another advantage of a vector gradiometer is that it can be built significantly smaller than classic gradiometers. Here a reference sensor is arranged so that its distance from the signal source is so large that the signal at the reference sensor is significantly smaller. This requires that the distance between the sensors is significantly greater than the distance between the source and the measurement sensor. By using vector information, all magnetometer units can be placed close to the source and no distant reference sensor is required.

Through calibration, an assumption regarding the distances to the signal origin or a reference sensor far from the source that characterizes the background field, a “map” can be created, i.e. a spatial resolution of the measurement signal (3D). A sensor array intrinsically provides 2D resolution. If you do not use a sensor array in one plane, a 2D resolution can be achieved.

The distance d between the sensor heads within a gradiometer unit, i.e. in this case the distance between the two sensor diamonds, can be in the range from mm to a few cm, for example between 0.5 cm and 2 cm. For values of this magnitude, good results could be achieved for measuring biomagnetic fields, which are in the picotesla range. As long as the signals are sufficiently independent of the background fields, larger or smaller distances or other gradiometer configurations can also be used, such as sensors arranged next to one another. If the distance between the individual sensor heads is too large, particularly in the case of local background fields (electrical lines, etc.), the background field can no longer be identical at both locations; However, if the distance between the sensor heads is too small, the difference between the field strengths of the magnetic field to be measured between the two locations may be too low. The choice of the appropriate distance between the two sensors of a gradiometer unit is therefore preferably also dependent on the type and orientation of the magnetic field source of interest and on the expected field strength. The distance of the sensor unit from the magnetic field source can also be in the mm to cm range.

4 shows in various figures a) to c) a top view of possible geometric arrangements of NV magnetometer units (illustrated by circles) of a device for detecting magnetic signals according to one embodiment. The NV magnetometer units are essentially arranged in one plane, that is, the distance between two NV magnetometer units in the (e.g. x/y) plane is at least twice as large as a difference in a height direction (z axis), which is unavoidable in practice ).

Figure a) shows a band of NV magnetometer units in a linear orientation, which conveniently runs transversely to a user's longitudinal body axis. In one embodiment, it is arranged in a base body to accommodate a user. Such a base body can in particular be a mattress, whereby the band should then be placed at a typical distance of the chest/heart area from the head end of the mattress (depending on the region and the size of the mattress). To achieve an ideal result, a distance between two adjacent NV magnetometer units should correspond to an average distance from the heart to the mattress, i.e. approx. 15-20 cm. This allows at least two NV magnetometer units to always measure the heart's magnetic field and the background field can be very effectively suppressed by varying the orientation of the heart's magnetic field based on the sensor position. The more distant NV magnetometer units in the band can be used as a zero reference (no MKG signal in the measured signal).

Figure b) shows a number of NV magnetometer units arranged as a polygon on the corners of triangles. Depending on how large a triangle is considered, NV magnetometer units also sit on the edges. This can be done using the example of the mattress 4a) a greater variance in the sleeping area can be achieved. This allows a wider sleeping area compared to a band and is optimal in terms of the number of NV magnetometer units used. In addition, the MKG signal is measured by at least three NV magnetometer units, which enables optimized noise and background suppression (full reconstruction of the heart's magnetic dipole possible). The more distant NV magnetometer units of the arrangement can be used as a zero reference (no MKG signal in the measured signal).

In ) a number of NV magnetometer units are shown, which are arranged on the circumference and on the center of a circle. This is advantageous in order to achieve the most accurate possible resolution of the cardiac signal and an optimal spatial resolution (e.g. to be able to determine the muscle signal from the atrium). The ring should have a diameter that is approximately twice the distance from the heart to the sensor plane/support surface. At least three NV magnetometer units should be installed in the circular arrangement. If there is a NV magnetometer unit at the center of the circle, it should be located as centrally as possible under the heart. Optionally, an arrangement of additional rings with larger diameters can be used.

In all examples, at least one further NV magnetometer unit can be placed in the room as an additional reference (zero signal, in which the heart signal can no longer be measured), e.g. under the bed, on a ceiling, wall, as an additional unit in order to be considered a distant one Reference to make a background field and noise easier to eliminate. In such an exemplary embodiment, the device therefore further has a further NV magnetometer unit for determining a background field, which is spaced at least 1 m from the at least two NV magnetometer units. This allows an additional improvement in noise reduction. Furthermore, several such (“reference”) NV magnetometer units can be networked with one another in order to form a network of stable reference sensors. In this way, interference fields, backgrounds and noise can be characterized even better and separated from the signal.

In one embodiment, multiple devices can be networked, such as different beds, and use this as a reference sensor when networking is set up. This can lead to correct mapping/determination of the course of geomagnetic field fluctuations or typical noise events in a building. In such an embodiment is an inventive Device set up to receive information about a background field from another device according to an exemplary embodiment of the invention.

QUOTES INCLUDED IN THE DESCRIPTION

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Cited patent literature

• DE 102022204526 [0002]
• DE 102022201690 [0010]

Claims (13)

Device for detecting magnetic signals generated by a beating heart (M). at least two nitrogen vacancy centers, NV, magnetometer units (S1, S2, ..., Sn; S11, S21, ..., Sn1, S12, S22, ..., Sn2, S1m, ..., Snm), which are arranged in a geometric, in particular essentially flat, arrangement relative to one another and are connected to a signal processing unit (170, 200), wherein the device is set up to a magnetic field strength by means of each of the at least two NV magnetometer units (S1, S2, ..., Sn; S11, S21, ..., Sn1, S12, S22, ..., Sn2, S1m, ..., Snm). (R1, R2) and field direction (R1, R2), and by means of the signal processing unit (170, 200) an effective magnetic field strength and field direction from which by means of the at least two NV magnetometer units (S1, S2, ..., Sn; S11, S21, ..., Sn1, S12, S22, .. ., Sn2, S1m, ..., Snm) to determine the detected magnetic field strength and field direction. Device according to Claim 1 , where the geometric arrangement is a two-dimensional arrangement in which the at least two NV magnetometer units (S1, S2, ..., Sn; S11, S21, ..., Sn1, S12, S22, ..., Sn2, S1m , ..., Snm) are arranged in one plane. Device according to Claim 2 , whereby the at least two NV magnetometer units (S1, S2, ..., Sn; S11, S21, ..., Sn1, S12, S22, ..., Sn2, S1m, ..., Snm) in a line are arranged. Device according to Claim 2 , whereby the at least two NV magnetometer units (S1, S2, ..., Sn; S11, S21, ..., Sn1, S12, S22, ..., Sn2, S1m, ..., Snm) on the edges and/or corners of a polygon are arranged. Device according to one of the Claims 2 until 4 , whereby the at least two NV magnetometer units (S1, S2, ..., Sn; S11, S21, ..., Sn1, S12, S22, ..., Sn2, S1m, ..., Snm) on the circumference and optionally arranged on the center of a circle. Device according to one of the preceding claims, wherein each of the at least two NV magnetometer units (S1, S2, ..., Sn; S11, S21, ..., Sn1, S12, S22, ..., Sn2, S1m, .. ., Snm) as the sensor medium (110) has a diamond crystal or a section of a diamond crystal with nitrogen vacancy centers, the device being set up to determine the magnetic field strength and field direction by reading out a spin resonance in the sensor medium (110) which is dependent on the magnetic field strength ) capture. Device according to Claim 6 , 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). Device according to Claim 7 , whereby the at least two NV magnetometer units (S1, S2, ..., Sn; S11, S21, ..., Sn1, S12, S22, ..., Sn2, S1m, ..., Snm) have the same excitation light source ( 120) and/or the same microwave source (150) are assigned. Device according to one of the Claims 6 until 8th , wherein the sensor medium of the at least two NV magnetometer units (S1, S2, ..., Sn; S11, S21, ..., Sn1, S12, S22, ..., Sn2, S1m, ..., Snm) respectively has a section of the same diamond crystal (110). Device according to one of the Claims 6 until 9 , 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) is between 1 and 30 millimeters, preferably between 5 and 20 millimeters. Device according to one of the Claims 6 until 10 , further comprising at least one device for generating a substantially homogeneous bias magnetic field at the location of the sensor media (110) of the at least two NV magnetometer units (S1, S2, ..., Sn; S11, S21, ..., Sn1, S12 , S22, ..., Sn2, S1m, ..., Snm), where the bias magnetic fields of different NV magnetometer units (S1, S2, ..., Sn; S11, S21, ..., Sn1, S12 , S22, ..., Sn2, S1m, ..., Snm) are different. Device according to one of the preceding claims, further comprising a further NV magnetometer unit for determining a background field, which is spaced at least 1 m from the at least two NV magnetometer units. Device according to one of the preceding claims, which is adapted to receive information about a background field from a further device according to one of the preceding claims.

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