Sensor unit and method for detecting brain-wave-induced magnetic fields

Abstract

The invention relates to a sensor unit for detecting brain-wave-induced magnetic fields in a non-shielded environment, comprising multiple gradiometer units (100, 200, 300, 400) which are designed to be arranged around the head of a user, wherein each gradiometer unit (100, 200, 300, 400) comprises two magnetometers (101, 102, 401, 402) that are arranged at a fixed distance from one another, wherein each magnetometer comprises a sensor medium (101, 102) and is designed to detect a magnetic field strength at a measuring site by reading a spin resonance in the sensor medium depending on the magnetic field strength, wherein the sensor unit also comprises at least one excitation light source (120) for radiating light (124) into the sensor medium (101, 102) of the magnetometer, wherein the sensor unit also comprises at least one signal processing unit (406) for determining a magnetic field gradient at a gradiometer unit (100, 200, 300, 400) as the difference between the output signals of the two magnetometers of the gradiometer unit and for detecting a temporal curve of the magnetic field gradient.

Description

[0001] Description

[0002] title

[0003] Sensor unit and method for detecting brainwave-induced magnetic fields

[0004] The present invention relates to a sensor unit and a method for detecting brainwave-induced magnetic fields as well as a computing unit and a computer program for carrying out the same.

[0005] Background of the invention

[0006] In various areas, it is necessary to detect a user's mental or physical state. This includes, for example, medical applications, for the timely detection of illnesses or critical conditions; but it is also of interest, for example, to automatically detect whether a user is fit to drive a vehicle or whether their ability to drive is impaired due to fatigue or a medical emergency.

[0007] Various methods are known for monitoring conditions such as fatigue. For example, eye movements and blinking frequencies can be monitored using camera images, and certain patterns can then be used to determine the user's ability to drive. However, this requires a continuous, unobstructed field of vision, which can be prevented by poor lighting, head movements, or glasses, for example.

[0008] Furthermore, measurement methods such as EEG (electroencephalogram), which measures potential changes distributed across the scalp, provide reliable information about a user's mental state, for example, for detecting fatigue or emergencies. However, electrodes must be correctly applied to the head and coated with contact gel for accurate measurement results, making EEG impractical as a measurement method in everyday applications, such as driver monitoring.

[0009] Disclosure of the invention

[0010] According to the invention, a sensor unit and a method for detecting brainwave-induced magnetic fields in an unshielded environment, as well as a computing unit and a computer program for implementing the method, are proposed. Advantageous embodiments are the subject of the dependent claims and the following description.

[0011] The invention creates a method suitable for everyday use and as contactless as possible for measuring brain waves and the associated mental or physical states of a user.

[0012] In particular, a sensor unit is proposed which comprises a plurality of gradiometer units which are configured for arrangement around a user's head. Each gradiometer unit comprises two magnetometers which are arranged at a fixed distance from one another. Each magnetometer comprises a sensor medium and is configured to detect a magnetic field strength at a measurement location by reading out a spin resonance in the sensor medium which is dependent on the magnetic field strength. The sensor unit further comprises at least one excitation light source for radiating light into the sensor media of the magnetometers and at least one signal processing unit which is configured to determine a magnetic field gradient at a gradiometer unit as the difference between the output signals of the two magnetometers of the gradiometer unit and to detect a temporal profile of the magnetic field gradient.By using sensitive magnetometers based on spin resonance effects and a gradiometer configuration, it becomes possible to effectively detect the desired signals evoked by brain waves, even in the presence of background fields such as the Earth's magnetic field or artificially generated magnetic fields. This eliminates the need for complex magnetic field shielding and complicated sensor handling, making it possible to use this sensor unit to measure brain activity in everyday environments.

[0013] According to a possible embodiment, at least one of the magnetometers can comprise a nitrogen vacancy center magnetometer, wherein the sensor medium comprises a diamond crystal or a section of a diamond crystal with nitrogen vacancy centers, and wherein the sensor unit further comprises at least one microwave source for generating a resonant field in the sensor medium and at least one photodetector for detecting resonance-dependent sensor light from the cell. Nitrogen vacancy (NV) center magnetometers are highly sensitive and thus well suited for detecting the weak brainwave magnetic fields. By using individual diamonds or a common diamond for several sensor heads, easy-to-use sensors are feasible that can be integrated into many devices. In particular, small light sources and photodetectors can also be directly connected to the diamonds - e.g.in the form of thin diamond plates—to form compact sensor heads. Magnetometers based on nitrogen vacancy centers also enable vector measurements of magnetic fields and offer high dynamic range.

[0014] In particular, in a gradiometer unit formed from two nitrogen vacancy center magnetometers, the two magnetometers of the at least one gradiometer unit can be assigned the same excitation light source and the same microwave source, so that a reliable suppression of all noise sources and background signals that occur with approximately the same intensity at both magnetometers of a gradiometer unit is possible.

[0015] Additionally or alternatively, at least one of the magnetometers can also comprise a vapor cell magnetometer, wherein the sensor medium comprises an atomic spin-polarizable vapor in a cell, wherein the atomic vapor comprises, for example, an alkali metal, a noble gas, or an alkali metal azide. Such cells can be easily manufactured on a small scale and also offer very high sensitivity. Such a sensor unit can comprise at least one holding device in which several gradiometer units are mounted such that, during operation, they are arranged at different locations close to the surface of a user's head. The distance between the two magnetometers of a gradiometer unit should be in the millimeter to centimeter range, for example between approximately 2 and 30 millimeters, preferably between 5 and 20 millimeters.With these approximate distances, it is possible to assume the background field to be uniform and effectively eliminate it, while the brain magnetic field signals of interest decrease with the square of the distance from the source and are thus significantly lower at one of the two magnetometers. The gradiometers can also be placed directly on the scalp or a few millimeters to centimeters away from the scalp, depending on the signal strength and the sensitivity of the sensor setup.

[0016] The holding device in which a sensor unit or the gradiometer sensors can be accommodated can, for example, comprise a headrest, a headgear, a headband, a pillow or the headboard of a bed. However, any other holding devices can also be used that allow the gradiometer units to be brought sufficiently close to the user's head. Optionally, holding devices can also be used in which the user's head can be held in the holding device in such a way that the head remains freely movable relative to the holding device. For example, headgear or straps are attached to the head in a removably manner, whereas in the case of a headrest or the headboard of a bed, the respective elements can be shaped so that the head can fit into them but is not fixed in place and does not have to rest directly against the holding device.Thus, the sensor unit according to the invention can also be used in everyday environments without restricting the user, such as in hospital beds, in emergency transport, for monitoring the conditions of a driver, train driver or pilot, or in any other areas.

[0017] Additionally, in some embodiments, the sensor unit may further comprise a position reference unit that can be worn on a user's head and is configured to determine a relative position or a relative movement between a user's head and the plurality of gradiometer units. Such a position reference is particularly useful in embodiments in which the position of the gradiometer units on the head can shift or in which free mobility of the head is provided, thus resulting in constant changes in the relative position. The reference signals can then be used to correct the received magnetic field signals or to evaluate the reference signals in combination with the magnetic field signals.

[0018] For example, at least one gyroscope or at least one element for generating a reference magnetic field (e.g., using permanent magnets or a coil) can be used as a position reference unit, which can be detected by magnetometers of the sensor unit. These position reference units can be worn in suitable elements on the user's head, such as a temple, an ear hook, a headband, or similar devices.

[0019] Furthermore, a method for detecting brainwave-induced magnetic fields using such a sensor unit is proposed, which comprises detecting magnetic field strengths by the magnetometers of the sensor unit in the head region of a user; determining, for each gradiometer unit, a magnetic field gradient by forming a difference signal from the output signals of the associated magnetometers; detecting a temporal progression of the magnetic field gradients for each gradiometer unit; and checking the temporal progression of one or more magnetic field gradients for the occurrence of predetermined patterns.The verification can be performed in the traditional way by comparing pattern parameters and evaluating curve parameters of the temporal progression; additionally or alternatively, machine learning methods can also be applied to check the recorded magnetic field signals for known, unknown, or undesirable patterns. Additionally, a position reference signal can be recorded, which serves to determine a relative position between the gradiometer units and the user's head. This signal can then be used together with the magnetic field gradient to determine a position-corrected progression of the magnetic field gradients. This evaluation of the position reference signals can also optionally be performed using artificially learning units.

[0020] The signal for establishing a position reference can, for example, comprise an additional brainwave-induced magnetic field signal, which is independent of the user's mental state, or a gyroscope signal from one or more gyroscopes attached to the user's head. Another possibility is a magnetic field signal generated by a position reference unit attached to the user's head. All of these methods can also be combined appropriately.

[0021] Furthermore, the method can include detecting, based on the temporal progression, an undesirable state of the user and initiating reactions based on the detection. The initiated reactions can be controlled in other devices and systems or executed by additional elements of the sensor unit (e.g., displays, signal generators) and otherwise depend on the application area of ​​the sensor unit. The undesirable state can include, for example, fatigue, stress, falling asleep, a neurological disorder such as Parkinson's disease, a stroke, epilepsy, or any other condition that results in a measurably altered brain activity of a user.

[0022] A computing unit according to the invention, e.g. a control unit of a motor vehicle or a controller of a patient monitoring system, is configured, in particular in terms of programming, to carry out a method according to the invention.

[0023] The implementation of a method according to the invention in the form of a computer program or computer program product with program code for carrying out all method steps is also advantageous, since this entails particularly low costs, in particular if an executing control unit is also used for other tasks and is therefore already present. Finally, a machine-readable storage medium is provided with a computer program stored thereon, as described above. Suitable storage media or data carriers for providing the computer program are, in particular, magnetic, optical, and electrical memories, such as hard disks, flash memories, EEPROMs, DVDs, and others. Downloading a program via computer networks (Internet, intranet, etc.) is also possible. Such a download can be wired or cable-based or wireless (e.g., via a WLAN network, a 3G, 4G, 5G, or 6G connection, etc.).

[0024] Further advantages and embodiments of the invention will become apparent from the description and the accompanying drawings.

[0025] The invention is illustrated schematically in the drawings using exemplary embodiments and is described below with reference to the drawing.

[0026] Short description of the drawings

[0027] Figure 1 shows schematically a possible structure of a sensor unit with a gradiometer structure;

[0028] Figure 2 shows schematically a headrest with several gradiometers;

[0029] Figures 3a and 3b show cross sections through exemplary holding devices for arranging sensor units around a user’s head; and

[0030] Figure 4 schematically shows the signal processing of the acquired gradiometer signals according to an exemplary embodiment.

[0031] Embodiments of the Invention The brain waves of a human user, which can be measured, for example, via potential changes on the scalp, provide clues to various mental, physical, or health conditions of the user. However, the electrical activity in the brain neurons also induces a weak magnetic field, which can be detected and evaluated by magnetic field sensors. The temporal progression of the induced magnetic fields can then also be used to draw conclusions about the brain wave patterns and thus about various conditions of a user.

[0032] Since the magnetic field strengths to be measured are very small, quantum-based or optically pumped magnetometers, which allow highly sensitive measurements, are particularly suitable as sensors for such a setup. In the following embodiments, only two sensor types are described as examples as possible magnetometers for the proposed sensor unit: vapor cell magnetometers and diamond NV magnetometers. However, it is also conceivable to integrate other magnetometers with comparable properties into the sensor unit.

[0033] The magnetometers described here as examples use optically pumped and / or optically detected magnetic resonance (ODRM). This method exploits the fact that the energy levels of certain spin states of unpaired electrons are split under the influence of an external magnetic field (Zeeman effect). The splitting of the 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.

[0034] 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. Details can be found, for example, in DE 10 2018 202 238 A1.

[0035] Since the NV center in single-crystal diamond has four possible arrangements in the crystal lattice, in the presence of a directed magnetic field, the NV centers present in the crystal respond to the external magnetic field with varying degrees of intensity depending on their position within the crystal. Ideally, this can result in four pairs of fluorescence minima appearing in the spectrum, from whose shape and relative positions both the magnetic field strength (magnitude) and the direction of the external magnetic field can be unambiguously determined.

[0036] The NV-center magnetometer offers a variety of advantages for this application. In addition to the aforementioned very high sensitivity, it can also cover a wide measurement range (> 1 Tesla). The underlying Zeeman effect is linearly dependent on the existing magnetic field and, moreover, exhibits no degradation because the measurement is based on quantum mechanical states. Furthermore, an NV-center magnetometer offers the possibility of vectorially determining external magnetic fields based on the various orientations present in the diamond lattice.

[0037] There are also alternative ways to electrically read magnetic spin resonance in diamond. This involves detecting charge carriers that have been lifted into the diamond's conduction band by two-photon ionization of the NV centers. If such a method is used to read resonance effects, components for detecting the fluorescent light are not required and are replaced by suitable photocurrent detectors on the diamond. Apart from that, the method can be adapted for magnetic field measurement and applied in all versions with NV center magnetometers.

[0038] Vapor cell magnetometers are also based on the readout of spin resonances. In this case, a cell, e.g., a closed cavity in a silicon wafer, is filled with gaseous atoms and, if necessary, additional buffer gases, e.g., vaporized alkali metals such as potassium, rubidium, or cesium, which also contain unpaired electrons. Depending on the design, mixtures of alkali vapor and noble gases can also be used. In other cases, pure noble gases are used.

[0039] In vapor cell magnetometers, spin polarization is also achieved through optical pumping with an excitation light source. Subsequently, the optical properties of the atoms in the cell are read out via resonance effects, e.g., with an additional readout light source, which measures the absorption of the readout light by the vapor cell. Different magnetic-field-dependent state splittings can be observed.

[0040] To be usable in everyday environments, magnetic fields that do not originate from brain activity should be eliminated from the measurement as much as possible. Especially in the automotive sector, comparatively high and barely shielded magnetic fields arise in the background, which are approximately in the range of 10' 6 up to 10' 9 Tesla (Nanotesla), in addition the Earth's magnetic field is in the range of 10' 5 Tesla (a few microtesla). In contrast, the biomagnetic fields of interest here are in the range of 10' 12 Tesla (Picotesla) or even less.

[0041] According to exemplary embodiments, the elimination of background magnetic fields can be achieved by using a gradiometer arrangement for magnetic field measurement. Gradiometers are generally sensor units capable of detecting not only the field strength but also the field gradient. For this purpose, at least two individual magnetometers arranged at spatially different locations can be used. As an example, a sensor unit using two NV center magnetometers in a gradiometer arrangement is described below.

[0042] Initially, a diamond with nitrogen vacancies can be present for each magnetometer. The optical excitation of the NV centers is achieved using a suitable light source such as a pump laser. An Nd:YAG laser in the green range at a frequency of 532 nm is suitable for exciting the respective transitions. The light from the pump laser can be irradiated into the diamonds using suitable optical elements such as mirrors, beam splitters, lenses, and, if necessary, fiber optic elements. A single light source is used for both diamonds, from which the excitation light is guided into each diamond via an optical fiber. Furthermore, the excitation light can be irradiated continuously or in pulsed mode by the laser, so that, for example, time windows are kept free for interference-free fluorescence light measurements.

[0043] The distance d between the diamonds corresponds to the distance between the locations where simultaneous magnetic field measurements are taken. As long as the distance between the measurement locations is relatively small, it can be assumed that the strength of the additional background magnetic field B envis approximately the same size at both locations. In contrast, the weak magnetic field induced by brain waves will decrease significantly with increasing distance from the skull or, more generally, from the magnetic field source. By placing two sensors at different distances from the measuring area, e.g., from the skull surface, the background field can be eliminated by forming a difference between the recorded sensor values, and the magnetic field of brain activity, or rather, its gradient, can be extracted. Since the magnetic field weakens with the square of the distance, the greatest change in the magnetic field is detected by the sensor diamond near the source. For this purpose, for example, two magnetometers can be arranged one above the other in an axial gradiometer configuration, i.e., essentially perpendicular to the skull surface.

[0044] The following applies to an axial gradiometer with a first and a second magnetic field sensor:

[0045] Bl= Bbrainl + Benv ,

[0046] B2 — Bbrain2 + Benv ,

[0047] Bgrad — Bl B2 — Bbrainl " Bbrain2 ~ Bbrainl where Bi is the measured field strength at the first sensor, which is closer to the magnetic field source of interest (in this case, the head), where Bbraini is the fraction of the magnetic field strength at the location of the first sensor that is induced by the brain waves, where B2 is the measured field strength at the second, more distant sensor, where Bbrain2 is the fraction of the magnetic field strength at the location of the second sensor that is induced by the brain waves, and where B gr ad is the resulting gradient of the magnetic field strength.

[0048] Since the magnetic field Bbrain2 induced by brain waves at the second sensor, which is further away from the source, is many times lower than at the first sensor, the gradient B grad of the total magnetic field at this point is approximately equal to the brainwave-induced magnetic field Bbraini at the first, closer sensor head, while the approximately uniform background fields B env be eliminated.

[0049] The distance d between the sensor heads within a gradiometer unit, in this case the distance between the two sensor diamonds, can range from mm to several cm, for example between 0.1 cm and 2 cm, preferably less than 1 cm. Good results have been achieved for measuring biomagnetic fields for values ​​in this range. However, 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 side by side parallel to the head surface. If the distance between the individual sensor heads is too large, particularly in the presence of local background fields (electrical cables, etc.), this can lead to poor results.) the background field may no longer be identical at both locations; if the distance between the sensor heads is too small, however, the difference between the field strengths from the brainwave magnetic field between the two locations may be too small. The choice of the appropriate distance between the two sensors of a gradiometer unit therefore preferably also depends on the type and orientation of the magnetic field source of interest (e.g., a specific brain region), the expected field strength, and the distance of the entire gradiometer unit from the magnetic field source—in this case, also the inevitable distance to the active brain neurons inside the head that induce the magnetic field.In addition to an axial gradiometer configuration as described above, in which the sensors are arranged practically along the direction of the measurement signal perpendicular to the head surface, other configurations are also conceivable. In particular, it is also useful to use multiple measurement axes, or specifically three measurement axes. An NV center sensor, which enables vector magnetometry, is particularly well suited for this. In these cases, the measurement directions perpendicular to the head surface can be used for corrections. In general, gradiometric arrangements can ideally compensate in all spatial directions, but especially in the measurement direction.

[0050] The arrangement of multiple sensors in a sensor array with one or more rows can also be used to achieve motion correction and detailed readings of different brain regions. Here, too, the sensors should be placed close together for efficient background suppression, again approximately within a millimeter range.

[0051] The distance of a sensor unit from the head can also be in the mm to cm range. When mounted directly on the user's head using hoods or similar mounts, a very short distance from the head is achieved, and thus a minimal distance from the magnetic field sources. When the sensors are arranged in a mount close to the head, the distances from the head can be a few mm to a few cm to achieve sufficiently large and detectable magnetic field strengths at the measurement site. The possible distance and arrangement also depend on the depth and orientation of the expected brain activity areas.

[0052] The described steam cell magnetometers can also be used in such gradiometer arrangements.

[0053] In addition, the sensor unit can contain a microwave source capable of generating an electromagnetic field in the region of the NV centers in the diamonds over a bandwidth that sufficiently covers the desired resonance frequency. Preferably, the same microwave source can be used for both sensors or diamonds, the field then being transmitted to the diamonds via a radio-frequency connector. In addition, a microwave resonator structure (not shown) can be present on each diamond to distribute the generated microwave field homogeneously across the volume of the sensor diamond.

[0054] The resulting fluorescent light can then be guided through the fiber optics and detected by a photodetector sensitive to the fluorescence wavelength; alternatively, one or more photodetectors could be arranged directly on the sensor diamonds to receive the fluorescent light. Suitable reflective or semi-transparent mirrors, filters, beam splitters, lenses for beam shaping, coupling lenses for fiber optics or for the diamond crystals, and other optical elements along the optical path of the fluorescent light can also be used here. The photodetector signal can then be further processed by various elements, such as a preamplifier or a processing unit for signal evaluation.

[0055] The elements of the sensor unit are shown only schematically in the figure; it is understood that, for example, the microwave source is designed and arranged to generate the RF field in the sensor diamonds. Other elements such as microwave resonators or housing components are also not explicitly shown here.

[0056] Instead of two sensor diamonds, as shown in Figure 1, a single diamond with NV centers could be used, which has a certain spatial extension at least along one direction to enable a gradiometer configuration. For this purpose, the diamond is excited at at least two locations and the resulting fluorescence light is read out by at least two suitably arranged photodetectors. For this purpose, a diamond waveguide with NV centers can be used, for example, so that the excitation light can propagate along the gradiometer axis in the waveguide and reach both readout locations. In the other direction, no great extension of the crystal is required, so that, for example, diamond platelets are conceivable as sensor heads. As long as both sensor diamonds orSince the same microwave source and the same light source are used for diamond sections, noise components from these sources (noise from the excitation light or frequency and amplitude noise from the microwave source) also occur at both sensor heads. These simultaneously occurring noise components are automatically eliminated by the gradiometer arrangement. This reduces the requirements for the noise characteristics of these components. For a microwave source, for example, a cost-effective standard oscillator with higher phase and amplitude noise can be used instead of a high-precision, expensive, and temperature-controlled quartz oscillator.

[0057] To further suppress the gradiometer's sensor noise, a modulation method can be used, for example, in which the microwave frequency or the amplitude of the microwaves is modulated. Modulating the microwave frequency with a specific modulation depth and modulation frequency generates a fluorescence modulation. Demodulating the detected fluorescence signal then yields a signal in the magnetic resonance frequency range that is linearly dependent on the magnetic field. Alternatively, or additionally, the light intensity of the excitation light can also be modulated.

[0058] Another particularly interesting option is to determine the location of the magnetic field source, thus enabling vector magnetometry. This involves determining the field gradient in three axes. The direction in which the magnetic field gradient is maximum indicates the location of the magnetic field source. For this purpose, an additional bias magnetic field can be generated using permanent magnets or coils, for example, which is identical at both measuring locations of the gradiometer (i.e. in the area of ​​the sensor heads or sensor diamonds). In one possible embodiment, a single cylindrical coil can be used for this purpose, within which the sensitive diamond sensors are located. Here, too, the use of a single coil and current source ensures that the same noise components can be expected at both sensors, which in turn are eliminated by the gradient formation.In addition to or as an alternative to a gradiometer configuration, lock-in detection can be used for a magnetometer to eliminate unwanted background fields from the measurement. For this purpose, for example, the excitation light or microwave source can be modulated, and a lock-in amplifier 134 can be provided in the signal processing area of ​​the sensor unit 100, which essentially acts as a narrowband bandpass filter for the resonance signal of interest.

[0059] As a further embodiment, gradiometer units can also be formed from two vapor cell magnetometers. While these vapor cell magnetometers often require strong magnetic shielding, as they are typically only operated at low field strengths close to the near-zero field, measurements can also be taken in normal ambient conditions using vapor cells with a gradiometer configuration or with suitable lock-in detection. Combinations of vapor cells and NV center magnetometers within a single gradiometer unit are also possible.

[0060] In order to read magnetic fields induced by brain waves, several individual magnetometers and / or several gradiometer units consisting of two magnetometers each can be arranged at various locations around a user's head to together form a sensor unit. Depending on their specific spatial arrangement, the potentials generated by individual neurons and the induced magnetic fields add up, so that magnetic field changes distributed across the entire head can be measured. For this purpose, the sensor unit can comprise a holding device in which several magnetometers or gradiometers are arranged. The associated additional elements of the sensor unit, such as the signal processing modules, light sources, etc., can either be integrated into the holding device or can be housed separately, e.g., in a separate housing.For example, compact gradiometer units can be formed with two sensors, each integrating a diamond, optical filters, photodetectors, and a microwave resonator. It is also possible to arrange a small light source (e.g., a laser diode) and a photodetector directly on the diamond, thus forming a compact sensor head. The electronics for control and signal processing can then be arranged outside the actual sensor heads. Each magnetometer of a sensor head can be formed as a separate unit, but a compact gradiometer unit could also be formed within a single housing, which can then be easily integrated into other devices.

[0061] In principle, a type of headgear or a holding device worn on the head can be used for the entire sensor unit or for parts of the sensor unit, e.g. for the multiple magnetometers or gradiometer units. If, for example, a user wears a helmet, such as a motorcyclist or pilot, one or more sensor units, gradiometer units or magnetometer sensor heads can be integrated directly into this helmet. Glasses temples, ear hooks, hearing aids and other devices worn on the head can also be combined with the sensor units described here and accommodate the sensor heads at a suitable location. Likewise, holding devices in the form of a continuous or net-like hood or, for example, similar to a hairband or headband, in which multiple sensor heads are accommodated and which can be placed on the head can be used.

[0062] In other cases, however, it is more comfortable if the sensor unit is arranged near the head without being directly attached to it. To monitor the condition of a driver in a vehicle, sensor units or parts thereof can be integrated, for example, into a headrest 260 of a seat element 270, as shown by way of example in Figure 2. In this case, a headrest can be specially designed such that, as a holding device for the gradiometer units, extensions 265 extend at least partially around the head at the sides and / or above the head, and several gradiometers 200 or magnetometers are arranged at various locations in these side parts 265. It is understood that the shapes of the headrest or the side parts 265 of the headrest preferably approximately follow the shape of the head in order to be able to bring the sensors 200 as close as possible to the desired measuring ranges.If the desired monitoring requires only detecting magnetic field signals primarily at the back of the head, a standard headrest with appropriately embedded sensor heads can also be used. In all variants, magnetometers and / or gradiometers can also be arranged at different heights.

[0063] Figures 3a and 3b show similar holding devices 360, such as headrests with multiple gradiometers 300 or magnetometers, in a cross-section. In Figure 3a, a conventional headrest 360 is extended on both sides by lateral extensions 365, in which multiple gradiometer units 300 are mounted. The individual gradiometers 300 can be arranged side by side around the head circumference, vertically one above the other, or offset. In the present example, multiple gradiometer units 300 are provided symmetrically on both sides. However, the position and spacing of the gradiometers can also be selected differently, depending on the brain regions to be monitored and the design of the holding device and the sensor unit.

[0064] It is understood that such headrest elements can also be further adapted to increase functionality and comfort. For example, as shown in Figure 3b, manually or automatically pivotable side elements 366 can be provided as holding devices, in which the sensor units 300 are arranged. These can be folded into an open position via hinges or other connections (shown in dashed lines in the figure) or moved directly to the user's head 310 (solid line). Furthermore, it would also be possible to move the holding devices 366 and / or parts thereof in any direction to enable the use of the sensor unit, for example, for different body sizes. In this way, a driver can first easily position themselves in the seat, and then the movable side elements 366 are moved closer to the head 310.This ensures that the sensor heads of the individual magnetometers or gradiometers can be positioned as close to the head as possible and correctly. In addition, gradiometer units 300 can also be arranged in a rear part 362 of the headrest, which is not movable. Other parts of the sensor unit, such as a power supply and means for signal processing, can then also be integrated into the holding devices or optionally also in the other parts of the headrest or, for example, in the seat. The sensor data recorded by the sensor unit can also be stored locally or can be transmitted to other modules or systems, e.g. via a wireless communication interface such as WLAN or Bluetooth. This also makes it possible for all sensor data to be transmitted wired or wirelessly to a processing unit before evaluation, with the signal processing only taking place there.A dedicated processing unit can be used as the processing unit, but it is also possible for a processing unit or control unit already configured for other purposes, such as a central control unit in a vehicle, to perform these tasks. Additionally or alternatively, it is possible for the processed signals and results, e.g., the detected user states or alarm signals, to be subsequently transmitted to other units.

[0065] Depending on the embodiment, the gradiometer units can each be designed separately, i.e., they can comprise two sensor heads with the associated light sources, detectors, optical elements, signal processing units, etc., and together form a complete sensor unit. In other cases, a sensor unit can comprise multiple gradiometers, and at least parts of the components used can also be used for multiple gradiometers in parallel. In particular, for example, a common evaluation unit 136 can be provided for several or all gradiometer units used in an application. It is also conceivable to use light sources, magnetic field sources, or microwave sources jointly for multiple gradiometers, as long as this is structurally possible.

[0066] Another area of ​​application for the sensor units according to the invention also includes monitoring a user's condition for medical reasons. For example, it would be possible to install sensor units in a pillow element or on a patient bed. Again, the individual magnetometers or gradiometers 100, 200, 300 can be positioned at different locations so that they cover different areas of a user's head during use.

[0067] For example, a preformed cushion element made of a suitable material, such as a rigid foam, could be used, providing a recess for the head, allowing for appropriate positioning. The sensor heads of the magnetometer or gradiometer units 300 can then be embedded at various locations within the recess, so that they at least partially surround the user's head during use, similar to the headrest described in connection with Figure 3a.

[0068] As a further possibility, a modified version of the described vehicle headrests from Figures 2 or 3 could also be provided on a bed, a stretcher, or a chair, so that the head, when in use, is located in suitably shaped holding devices such as brackets or shell elements that are attached to the bed or chair and which, as in Figure 3b, can optionally also be designed to be pivotable or movable to enable correct positioning and convenient entry. This allows, for example, a patient's brain functions or vital functions to be continuously monitored without the need for sensors to be first applied by qualified personnel, as is the case with an EEG, and without unduly restricting the patient's normal movement.

[0069] To enable precise evaluation of the measured magnetic fields, it is useful to know the position of the head relative to the individual gradiometers or magnetometers as precisely as possible. If the magnetometers are not attached directly to the user's head, but are stationary, this relative position can change, since the intended applications do not expect the user to hold their head constantly in one position. Therefore, in all embodiments, additional modules or method steps can optionally be used to determine the relative head position relative to the measuring units. For this purpose, one or more gyroscopes attached to the user's head 310 can be used as the position reference module 380, for example. Suitable elements for this purpose include special eyeglass temples, attachments for existing eyeglasses, ear hooks, headbands, or other elements that allow defined positioning on the head.During operation, the user can wear at least one of the gyroscope modules at a defined location on their head, while the brainwave magnetic fields are measured as described above. The gyroscope can then be used to continuously track head movements in three dimensions, and suitable models can be used to determine the resulting shifts in the measurement locations for the magnetometers relative to the head. These changes can then be taken into account when evaluating the magnetometer or gradiometer signals.

[0070] In principle, all types of gyroscopes can be considered for this additional position reference module. Particularly suitable, for example, are the widely used MEMS (microelectromechanical system) gyroscopes, which are small and sufficiently sensitive. These sensors are usually built as a complete sensor system similar to an integrated circuit and can include sensors for one or more axes.

[0071] Likewise, other gyroscopes can also be used for relative position determination in a position reference module. In a similar way to the application as magnetometers, vapor cells and NV centers in diamond can also be used for spin-based optical measurement of rotation rates, forming highly sensitive gyroscopes. In these cases, the spin Larmor precession warmor is read directly. An external rotation of the gyroscope represents an additional rotation, which can be determined by reading the rotation frequency w me ss can be determined,

[0072] UJmess — UJlarmor ± UJrot

[0073] For example, DE 10 2019 219 061 A1 discloses a method for measuring three rotation directions using an NMR gyroscope. Since the relationship between the gyroscope signals on the head and the magnetic field measurements is not trivial, artificially learning units can also be used for the combined evaluation of the gyroscope signals and the brain magnetic field measurements. These units are trained, for example, on the combination of the two signals in predefined head positions. The result can then be a corrected magnetic field measurement, so that comparable signals are available in every head position, which can then be evaluated accordingly. Alternatively, the evaluation of known brain magnetic field patterns can also be applied directly to the combination of the two signals.

[0074] Another possibility for taking the relative head position into account compared to fixed magnetometers is the generation of a reference magnetic field. For this purpose, weak coils or permanent magnets similar to the described gyroscopes can be attached to suitable elements worn on the user's head as a position reference module 380. The measured static reference magnetic field and its change during head movement can then provide information about the relative position of the head 310 relative to the sensor unit or relative to the individual gradiometer units 300. If signals of different frequencies are expected, lock-in detection can also be used, for example, to separate the signals from one another and evaluate them correctly.

[0075] In addition, the head position can be determined by measuring another brain signal that is not influenced by the user's state (e.g., fatigue), preferably a signal that changes only with the head's position relative to the sensor. Such a signal can then be used as a reference signal for the head's position relative to the sensor unit. Signals of different frequencies can be differentiated using suitable signal processing, such as filters or lock-in detection. The position correction measures for magnetic field measurements described here can be used individually or in any combination.

[0076] If a user-attached gyroscope is used as a position reference module, its signals can also be used for separate status evaluation or other purposes. For example, certain movement patterns that may indicate drowsiness or emergencies, such as a lack of movement over a specified period of time, can be detected and evaluated. The results of the movement monitoring can then be evaluated individually or in combination with the results of the magnetic field measurements. Of course, a gyroscope can also be used solely for this purpose.

[0077] In all possible embodiments, an evaluation unit can be connected to the actual magnetometer and the associated detectors, which in particular enables electronic or computer-assisted evaluation of the detected signals. The signal processing is shown schematically in Figure 4. For each gradiometer 400, the raw signals of the individual magnetometers 401, 402 can optionally first be filtered via a low-pass filter 404, so that all noise components with frequencies significantly above the brain signal frequencies are eliminated. Subsequently, the difference 406 of the individual sensor signals can be formed for each gradiometer 400 according to a gradiometer arrangement, e.g., in a logarithmic differential amplifier. The difference signals can be further processed in a suitable manner, e.g.,by preamplifiers, filters, or other signal processing units 407, which can be provided individually for each gradiometer or for several gradiometers in combination. The temporal course of the magnetic field signals can then be evaluated in a pattern recognition unit 408, e.g., with reference to certain known or unknown patterns or to certain parameter properties. For this purpose, a neural network with several layers is shown in this example; however, any other unit for pattern recognition, with or without machine-learning components, can also be used. This is followed by the evaluation unit 409, which triggers certain reactions based on the recognized patterns.Pattern recognition, evaluation and classification of the recognized patterns as well as the selection of the corresponding reactions for a recognized pattern can also overlap, so that both functions can be performed by a single unit or divided differently.

[0078] To evaluate the recorded brain magnetic field signals, conventional methods such as various pattern recognition procedures, simple thresholds, temporal profiles, tolerance ranges, gradients, frequency evaluations, and others can be used. The respective reference values ​​can be stored in the system and assigned to specific conditions or illnesses, such as fatigue, stress, but also neurological disorders such as Parkinson's disease, epilepsy, or strokes.

[0079] Alternatively or additionally, artificial / machine learning, e.g., in the form of a neural network 408, can also be used at this point to evaluate the measured signals and classify them appropriately. For example, a neural network can also be trained with data obtained in the laboratory, which can optionally also be evaluated using other measurement methods such as EEG as a reference. Based on this data, an artificially learning unit can then detect, for example, fatigue or stress.

[0080] Since there is a certain degree of variation in the representative brainwave patterns between different users, current measurement data from a user can also be saved and included in the further analysis, particularly when using an artificially learning analysis system. For this purpose, data from the ongoing operation of a sensor unit can be used, for example, as user-specific training data for a neural network. Even with a classic pattern analysis, current data can in principle still be included and used, for example, by changing certain predefined limit values ​​or parameters for the future analysis of the measured magnetic field patterns. In addition, it is also possible for the system to evaluate any deviation of the recorded signal patterns from known reference states, even if no corresponding health condition of a user can be linked to it.In this way, unexpected or unknown changes in the detected brainwave patterns can be included and, for example, transmitted to another module for further manual evaluation.

[0081] If the described sensor units are used in a vehicle, various reactions can be triggered based on an evaluation of the measured magnetic fields. For example, the evaluation can be used to check whether fatigue or a medical emergency is present. If a condition is detected that indicates fatigue or even the onset of sleepiness, a warning can be issued. For example, a warning message can be displayed on a display to prompt the driver to take a break. Additionally or alternatively, acoustic or visual warning signals can be issued, which can also help prevent sleepiness.

[0082] Another possible application of driver condition monitoring is the ability to respond quickly to emergencies. For this purpose, brain magnetic field measurements can be checked for patterns that indicate certain illnesses or critical health conditions. Depending on the urgency, a warning can then be issued or emergency responses can be triggered. For example, if a critical condition is detected, an emergency signal could be transmitted via the vehicle's existing communication interfaces, alerting emergency services or other designated agencies.

[0083] It is also possible to make certain driving functions dependent on the detected brainwave patterns or the associated driver states. For example, it is conceivable to activate an automatic absolute speed limit for a tired driver, or to activate a driver assistance system such as lane departure warning or speed limit assist. Optionally, this activation can only be suggested to the user, and the actual activation can only be carried out after user confirmation.

[0084] In vehicles that are at least partially equipped with autonomous driving functions, certain driving functions can be made dependent on whether a driver is detected as alert and alert. For example, certain functions, such as fully autonomous driving, can only be permitted to a driver in a normal state.

[0085] If a critical condition has been detected by the brain magnetic field measurements and a driver no longer appears to be able to drive the vehicle safely, an autonomous driving function can, for example, initiate a drive to a parking space or another safe position.

[0086] Similar reactions are also conceivable in other areas of application. Even when the sensor unit is integrated into a patient bed, warning signals can be issued, particularly when a critical or unclear condition is detected. The signals can be issued in the immediate vicinity of the sensor unit or transmitted via communication media, for example, to a hospital monitoring unit. More detailed evaluations can also be performed, which can then be displayed to medical personnel for a quick overview, e.g., an automatic or semi-automatic diagnostic classification of the measured brain signals.

[0087] In all variants, the recorded sensor data can be evaluated, stored locally, and / or transmitted to other modules and systems. This also makes it possible, for example, in the event of a critical health condition, to transmit the corresponding measurement data from the magnetic field sensors directly to helpers on site, to a central monitoring point (e.g. in a clinic), or to an emergency call center so that this data can be used for further diagnostics. For example, a short-range radio interface such as a Bluetooth interface could be provided, via which the sensor data is transmitted from a storage element on request or automatically when a suitable reader approaches. In addition to the sensor data, the detected user states or other parameters can also be saved or transmitted additionally or alternatively.The magnetic field sensor data can also be supplemented by additional data from separate sensors and modules, such as camera images, measured temperatures, stored information about the user such as name and important health data, or information about the previous journey. A complete additional condition monitoring system can also be present and, in combination with the magnetic field data, used to decide on reactions, e.g., by evaluating the user's eye movements in camera images.

[0088] While the exemplary embodiments described gradiometers consisting of two identical magnetometers, gradiometer units can of course also be formed from different magnetometers, e.g., an NV center magnetometer and a vapor cell magnetometer. Again, this allows interference to be minimized or eliminated. Even in configurations where no gradiometer array is used, but the individual magnetometers are evaluated separately, several different types of magnetometers can be used in one sensor unit. It is also possible to configure identical or different magnetometers within a sensor unit for different detection frequencies and thus optimize them for different brain signals.

[0089] It is understood that the exemplary embodiments described here are intended only to illustrate the inventive principle, and that the measurement and evaluation of the magnetic fields generated by brain waves is possible in the manner described in many other situations and areas of application. In particular, such a system is not only suitable for car drivers or motorcyclists, but also for all operators of safety-relevant equipment, such as train drivers, pilots, or machine operators. Likewise, the various evaluation options can be applied to all examples. For example, a system for detecting neuronal abnormalities in a medical environment for the non-invasive monitoring of patients could be of interest, but also in the aforementioned vehicle applications or other situations. The different exemplary embodiments and elements can also be combined as desired.This allows various gradiometer configurations and magnetometer types to be used in all suitable mounting devices for mounting on a head. Other methods for position correction via a position reference module can also be combined with all variants and application areas. In addition to the embodiments described here for magnetometers with microwave field irradiation, other variants are also conceivable in which an applied external magnetic field, due to the Zeeman effect and suitable spin polarizations, exhibits an analyzable resonance signal in an optically detected resonance spectrum.

Claims

Claims 1. Sensor unit for detecting brainwave-induced magnetic fields in an unshielded environment, comprising: several gradiometer units (100, 200, 300, 400) arranged around a user's head, each gradiometer unit (100, 200, 300, 400) comprising two magnetometers (101, 102, 401, 402) arranged at a fixed distance from each other, each magnetometer comprising a sensor medium (101, 102) and configured to detect a magnetic field strength at a measurement location by reading out a spin resonance in the sensor medium that depends on the magnetic field strength, the sensor unit further comprising at least one excitation light source (120) for illuminating light (124) into the sensor media (101, 102) of the magnetometers, the sensor unit further comprising at least one signal processing unit (406) for Determining a magnetic field gradient at a gradiometer unit (100, 200, 300,400) as the difference between the output signals of the two magnetometers of the gradiometer unit and for recording a time course of the magnetic field gradient.

2. Sensor unit according to claim 1, wherein at least one of the magnetometers (101, 102, 401, 402) comprises a nitrogen vacancy center magnetometer, wherein the sensor medium comprises a diamond crystal (101, 102) or a section of a diamond crystal with nitrogen vacancy centers, and wherein the sensor unit further comprises at least one microwave source (140) for generating a resonant field in the sensor medium and at least one photodetector (130) for detecting resonance-dependent sensor light (125) from the sensor medium.

3. Sensor unit according to claim 2, wherein at least one of the gradiometer units is formed from two nitrogen vacancy center magnetometers (101, 102), and wherein the two magnetometers of the at least one gradiometer unit are assigned the same excitation light source (120) and the same microwave source (140).

4. Sensor unit according to one of the preceding claims, wherein at least one of the magnetometers comprises a vapor cell magnetometer, and wherein the sensor medium comprises an atomic spin-polarizable vapor in a cell, the atomic vapor comprising one of the following: an alkali metal, a noble gas, an alkali metal azide.

5. Sensor unit according to one of the preceding claims, wherein the sensor unit comprises at least one holding device (260, 265, 360, 362, 365, 366) in which several gradiometer units (100, 200, 300, 400) are mounted such that they are arranged at different locations near the head surface of a user during operation.

6. Sensor unit according to one of the preceding claims, wherein the distance (d) between the two magnetometers (101 , 102) of a gradiometer unit is between 2 and 30 millimeters, preferably between 5 and 20 millimeters.

7. Sensor unit according to one of the preceding claims, wherein the holding device comprises one of the following: a headrest, a head covering, a headband, a pillow, a headboard of a lounger.

8. Sensor unit according to one of the preceding claims, wherein the user's head can be received in the holding device in such a way that the head remains freely movable relative to the holding device.

9. Sensor unit according to one of the preceding claims, wherein the sensor unit further comprises a position reference unit (380) mounted on the head is portable by a user and is designed to determine a relative position or relative movement between the head of a user and the multiple gradiometer units (300).

10. Sensor unit according to claim 9, wherein the position reference unit (380) comprises at least one gyroscope or at least one element for generating a reference magnetic field which can be detected by magnetometers of the sensor unit.

11. Method for detecting brainwave-induced magnetic fields using a sensor unit according to one of the preceding claims, wherein the method comprises: Detection of magnetic field strengths by the magnetometers of the sensor unit in the head area of ​​a user; Determine, for each gradiometer unit, a magnetic field gradient by forming a differential signal from the output signals of the associated magnetometers; Recording a time course of the magnetic field gradients for each gradiometer unit; and Checking the temporal evolution of one or more magnetic field gradients for the occurrence of predefined patterns.

12. Method according to claim 11, further comprising: Acquiring a position reference signal, which serves to determine a relative position between the gradiometer units and the head of a user, and processing the position reference signal and the magnetic field gradients to determine a position-corrected course of the magnetic field gradients.

13. The method of claim 12, wherein the signal for forming a position reference comprises one of the following: an additional brainwave-induced magnetic field signal that is independent of a user's mental state; a gyroscope signal from one or more gyroscopes attached to a user's head; a magnetic field signal generated by a A position reference unit is generated that is attached to the user's head.

14. A method according to any one of claims 11 to 13, wherein the method further comprises: Detect, based on the review of the temporal progression, an undesirable user condition, and Initiating reactions based on detection.

15. Method according to any one of claims 11 to 14, wherein the undesired condition comprises one of the following: fatigue, stress, difficulty falling asleep, a neuronal disease, stroke, epilepsy.

16. Computing unit configured to perform all process steps of a method according to any one of claims 11 to 15.

17. Computer program that causes a computing unit to perform all the process steps of a method according to any one of claims 11 to 15 when executed on the computing unit.

18. Machine-readable storage medium with a computer program stored thereon according to claim 17.

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