Magnetic field detection device for detecting magnetic signal originating from measurement site

Abstract

The invention relates to a magnetic field detection device (300) for detecting a magnetic signal originating from a measurement point (330), comprising a magnetic field measurement unit (310) having at least one nitrogen vacancy center (NV) magnetometer unit, which is connected to a signal processing unit (340), the magnetic field measurement unit (310) being arranged on a movable manipulator unit (315), wherein the magnetic field detection device (300) is configured to move the magnetic field measurement unit (310) into at least two different positions relative to the measurement site (330) by means of the movable manipulator unit (315) and to detect a magnetic field strength and a field direction at each of the at least two different positions, and determining, by means of the signal processing unit (340), at least one field vector comprising an effective magnetic field strength and an effective field direction as a function of the magnetic field strength and the field direction detected at the at least two different positions.

Description

Technical Field

[0001] The present invention relates to a magnetic field detection device for detecting a magnetic signal originating from a measurement location. Background of the Invention In order to measure extremely small magnetic field intensities, suitable sensors are particularly optically pumped quantum sensors or quantum sensors based on NV centers in diamond. DE 10 2022 204 526.2 describes a magnetometer using optically pumped and optically detected magnetic resonance (ODMR). This utilizes the so-called Zeeman effect, in which the energy levels of certain spin states of unpaired electrons split under the influence of an external magnetic field. This energy level splitting produces altered transitions during relaxation from the excited state, 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 magnetic field strength can then be inferred from the measured optical parameters. Summary of the Invention

[0003] According to the invention, a magnetic field detection device for detecting magnetic signals originating from a measurement location is proposed, which has the features of claim 1. Advantageous embodiments are the subject matter of the dependent claims and of the description below.

[0004] The present invention proposes arranging a magnetic field measurement unit with at least one nitrogen-vacancy center (NV) magnetometer unit on a movable manipulator unit to detect the magnetic field strength and field direction, i.e., the magnetic field vector, at different positions relative to the measurement location, thereby determining the effective magnetic field vector. This movable arrangement enables a single magnetic field measurement unit to measure multiple different positions relative to the measurement location, thereby obtaining a three-dimensional image of the dominant magnetic field (particularly the magnetic field originating from an object at the measurement location). This movable arrangement enables a three-dimensional reconstruction of the magnetic field source distribution (e.g., underlying magnetic dipoles or currents). The present invention provides a magnetic field detection device that can be used for imaging, for example, in the manner of a computed tomography scanner or magnetic resonance imaging device.

[0005] Specifically, a magnetic field detection device for detecting magnetic signals originating from a measurement location is now introduced, comprising a magnetic field measurement unit having at least one NV magnetometer unit, the magnetic field measurement unit being connected to a signal processing unit, wherein the magnetic field measurement unit is disposed on a movable manipulator unit. The magnetic field detection device is configured to move the magnetic field measurement unit to at least two different positions relative to the measurement location with the aid of the movable manipulator unit, and to detect the magnetic field strength and field direction at each of the at least two different positions; and to determine, with the aid of the signal processing unit, at least one field vector including an effective magnetic field strength and an effective field direction based on the magnetic field strength and field direction detected at the at least two different positions. Either a wireless connection or a wired connection can be provided between the sensor device and the signal processing unit.

[0006] Diamond NV magnetometers are based on reading the magnetic resonance of specific defect centers in diamond—in particular, nitrogen vacancies (NVs), which occur as impurities in the diamond's carbon lattice and can also be introduced in a targeted manner. When 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, for example, 532 nm for non-resonant excitation), the electrons transition from the triplet ground state to the excited triplet state and relax to emit fluorescence in the red wavelength range of 650-800 nm (637 nm = zero phonon line). Due to the spin quantum number m, the electrons are excited in the ground state. s = The probability of non-spin-holding transition of the spin state of 1 is higher, so the continuous excitation pump makes most of the NV centers in m s = 0 is hyperpolarized.

[0007] In the ground state, m s =0 and m s = There is an energy difference between the spin states of m and n, which in this case is about 2.87 GHz. Therefore, if microwave radiation is incident on the diamond in addition to optical excitation, a sudden drop in red fluorescence occurs at the resonant frequency of 2.87 GHz, as the spin-polarized electrons are transported from m to n by the microwave field. s =0 ground state is elevated to m s = 1 ground state, and from there it is excited by the pump light to m s = 1 excited state. However, from there, nonradiative transitions occur mainly through the singlet state and weak infrared fluorescence transitions, while fluorescence in the red range disappears.

[0008] Now, if there is an external (to be measured) magnetic field, then due to the so-called Zeeman effect, the originally same energy ms = The triplet energy level will split into Zeeman energy levels with equal energy distance. Therefore, when the fluorescence spectrum corresponding to microwave excitation is plotted, two dips are shown in the fluorescence spectrum. The frequency spacing of these two dips is proportional to the magnetic field strength of the external magnetic field. Here, the magnetic field sensitivity is mainly defined by the minimum resolvable frequency shift and can reach 1 Because NV centers have four possible arrangements in the crystal lattice of single-crystal diamond, when an additional bias magnetic field is applied, the NV centers present in the crystal react to the external magnetic field with varying intensities depending on their location within the crystal. Ideally, this results in four pairs of fluorescence minima appearing in the spectrum, and their shapes and relative positions allow the strength (magnitude) and direction of the external magnetic field to be unambiguously determined.

[0009] If vector magnetic field measurements are to be performed, the magnetic field detection device also includes a device for generating a bias magnetic field in the region of the sensor medium. This can be a Helmholtz coil array, with at least the sensor medium arranged within the array. Other devices are also possible, such as simple coils, elongated coils, permanent magnet solutions (such as Halbach arrays), etc. In order to additionally determine vectorial (direction-dependent) magnetic field information, it is necessary to define the direction of the bias magnetic field.

[0010] Since measurements are taken at different locations, these locations have different orientations relative to the magnetic field at the measurement location. This allows the location and strength of the magnetic field to be determined. Since the background field (particularly the Earth's magnetic field) is generally essentially the same (same strength and orientation) at different locations, the background field can be eliminated. This eliminates the need for magnetic shielding, but to improve measurement results, the magnetic field detection device can also be magnetically shielded from the environment.

[0011] Another advantage of NV sensor devices is their size, particularly the size of the sensor medium. NV sensor devices have a very small active sensor volume. This miniaturization also enables the use of these sensors in geometric arrays. In particular, the very small active sensor volume allows for very high-resolution arrays.

[0012] In one embodiment, the magnetic field detection device is configured to determine the effective magnetic field strength and effective field direction based on the difference in magnetic field strength and field direction detected at at least two different locations. This is similar to the arrangement of a gradiometer with two magnetic field measuring units at different locations (circuit-based gradiometry), but it uses only one magnetic field measuring unit and calculates its measurement results, thus corresponding to a computer-based gradiometry. Through gradiometry, which involves performing basic vector operations on the measured values, the magnetic field gradient is approximately equal to the field emitted by the source, while the much stronger background fields (which are essentially the same at both locations) are eliminated (see also above). Therefore, the present invention is particularly suitable for unshielded measurement of weak magnetic fields. Technical details of the gradiometer concept, which is also applicable within the scope of the present invention, are disclosed in DE 10 20 22 20 16 90.4 and are incorporated herein.

[0013] In one design, at least two different positions are equidistant from the measurement location or an axis passing through the measurement location. In other words, the magnetic field measuring unit moves on a circular or spiral path around the measurement location or the axis. Spiral paths are particularly suitable for extended objects, such as a person positioned along an axis (e.g., lying on a couch). This approach is technically simple to implement and is already known and applicable in other applications (such as computed tomography). Furthermore, it makes it very easy to always find two different positions that are well-suited for computed gradiometric measurement.

[0014] In one embodiment, each of the at least two different positions lies on a straight line with the measurement location or a point on an axis passing through the measurement location. In other words, on a circular trajectory centered on the measurement location, the two measured positions are rotated 180° relative to the measurement location, for example, 90° and 270°. This makes it particularly easy to eliminate background fields.

[0015] In one embodiment, the magnetic field measurement unit includes at least two NV magnetometer units arranged in a plane. This allows, for example, a very simple circuit-based gradiometric method to be implemented. It also allows, for example, the determination of multiple field vectors, each comprising a magnetic field strength and a field direction, based on the magnetic field strength and field direction detected at at least two different locations.

[0016] Further advantages and configurations of the present invention can be gathered from the description and the drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] The present invention is schematically illustrated according to embodiments in the drawings and will be described below in conjunction with the drawings.

[0018] Figure 1The main components of a magnetic field measuring unit with an NV magnetometer unit, which can be used within the framework of the present invention, are shown in a schematic block diagram.

[0019] Figure 2 A schematic diagram shows an exemplary magnetic field measurement unit with multiple NV magnetometer units for use in a magnetic field detection device according to an embodiment of the present invention.

[0020] Figure 3 An exemplary magnetic field detection device according to one embodiment of the present invention is shown in a schematic diagram.

[0021] Figure 4 The diagram schematically shows the measurement of a magnetic signal in a magnetic field detection device according to one embodiment of the present invention. DETAILED DESCRIPTION

[0022] Figure 1 The main components of a magnetic field measurement cell with an NV magnetometer cell according to one design are schematically shown. Here, a diamond 110 containing nitrogen vacancies (NV) serves as the sensor medium. Optical excitation of the NV centers can be achieved using a suitable light source 120, such as a pump laser. Suitable examples include frequency-doubled Nd:YAG lasers or semiconductor lasers in the green range of approximately 510-532 nm (e.g., 532 nm for non-resonant excitation). Alternatively, LEDs in a suitable wavelength range can be used. Depending on the arrangement, the light from light source 120 can be injected into the diamond 110 via suitable optical elements 122, such as mirrors, beam splitters, focusing optics such as lenses, and, if necessary, fiber optic elements. Furthermore, the excitation light from the laser can be injected continuously or pulsed, for example, to preserve a time window for interference-free fluorescence measurement.

[0023] Furthermore, the magnetic field measurement unit can include a microwave source 150 capable of generating an electromagnetic field in the sensor medium (i.e., in the region of the NV centers of the diamond 110) within a bandwidth covering the desired resonant frequency. A microwave resonant structure can be used to uniformly distribute the generated microwaves over the volume of the measurement region in the diamond. The resonant structure or microwave source 150 is preferably tuned to the frequency of electron spin resonance. To enable vector magnetometry, an additional bias magnetic field is generated using device 140. This makes the measurement vectorial in nature. To this end, different spatial directions in the crystal structure are utilized. For example, Helmholtz coils are suitable for generating such a magnetic field, where a substantially uniform magnetic field can be generated within a limited region using a pair of coils. Other devices 140 are also possible, such as simple coils, elongated coils, or permanent magnet arrangements (e.g., Halbach arrays).

[0024] Fluorescence 112 generated from diamond 110 can be directed via suitable optical elements 134 (e.g., filters, beam splitters, lenses, and / or optical fiber elements) to a first photodetector 130, which is sensitive at least within the fluorescence wavelength range. This first photodetector 130 can also be positioned directly on diamond 110. A second photodetector 132 is positioned to detect at least a portion of the excitation light from light source 120, which can be coupled out via, for example, a beam splitter, filter, or semi-transparent element. The detector signal of this excitation light can be used as a reference signal to eliminate background signals and highlight resonant signals of interest, for example by modulating the excitation light with a lock-in amplifier. Additionally or alternatively, this reference signal can be used to account for fluctuations in the excitation light. Accordingly, corresponding circuitry 160 (e.g., preamplifier, logarithmic amplifier, lock-in amplifier, signal filter, etc.) is provided to acquire the signals from the first and second photodetectors and to appropriately pre-process them for further evaluation. Finally, the pre-processed fluorescence signal can be evaluated by a signal processing unit 170 (eg using a suitable microcontroller or processor) in order to obtain from the signal desired parameters of the detected magnetic field, in particular the magnetic field strength and direction.

[0025] It should be understood that such a device may also have other units not shown, such as a communication unit or an interface for outputting measurement results. Such a device may also be advantageously integrated into an ASIC or FPGA.

[0026] Such a magnetic field measurement unit with an NV magnetometer cell offers numerous advantages for this application. In addition to the already mentioned very high sensitivity, it can cover a wide measurement range (>1 Tesla). The underlying Zeeman effect is linearly dependent on the existing magnetic field and exhibits no degeneracy, as the measurement is based on quantum mechanical states. Furthermore, the NV magnetometer cell offers the possibility of vectorially determining the external magnetic field based on the different orientations present in the diamond lattice.

[0027] There is also the alternative possibility of electrically reading the magnetic spin resonance in diamond. Here, the charge carriers that are elevated into the diamond's conduction band due to two-photon ionization of NV centers are detected. If this method is used to read the resonance effect, the components used to detect fluorescence in the previous examples are no longer necessary and can be replaced by suitable photocurrent detectors on the diamond. Furthermore, the methods used for magnetic field measurement can be adapted accordingly and applied to all embodiments with NV magnetometer cells.

[0028] To enable use in everyday environments, magnetic fields not originating from desired weak sources should be eliminated from the measurement as much as possible, especially those around 10⁻ 5 The Earth's magnetic field in the range of Teslas (tens of microteslas).

[0029] Background magnetic fields can be eliminated by using shielding or gradiometers in magnetic field measurements according to exemplary embodiments. In principle, a gradiometer is a magnetic field measuring unit that can detect not only the field strength but also the field gradient. To this end, measurement information can be calculated between at least two spatially different locations.

[0030] exist Figure 2 FIG2 schematically illustrates a partial view of an exemplary magnetic field measurement unit 200 having multiple NV magnetometer cells used in a magnetic field detection device according to an embodiment of the present invention. The multiple NV magnetometer cells are arranged in a regular two-dimensional array on a substrate 201 (e.g., a printed circuit board PCB) on a plane.

[0031] Each NV magnetometer cell comprises a sensor medium 210 in the form of a diamond crystal, each of which is associated with a microwave resonator 251, which is connected to a microwave source 250 (for example in the form of an integrated circuit IC) via a waveguide 252. Other components, such as an excitation light source for injecting light into the sensor medium 210 and a device for generating a bias magnetic field in the region of the sensor medium 210, are not shown, but may be associated with all sensor media 210 in common. In addition, each sensor medium 210 may be associated with a (own) detector, for example in combination with Figure 1 As described.

[0032] Figure 3 A schematic diagram shows an exemplary magnetic field detection device 300 according to one embodiment of the present invention. The illustrated magnetic field detection device 300 includes a couch 320 for accommodating a patient 330 , who serves as the measurement location. Furthermore, the magnetic field detection device 300 includes a magnetic field measurement unit 310 with at least one NV magnetometer unit, which is connected to a signal processing unit 340 . The signal processing unit 340 can also serve as the control unit for the magnetic field detection device 300 .

[0033] The magnetic field measuring unit 310 is arranged on a movable manipulator unit 315, which is configured to move the magnetic field measuring unit 310 in a circumferential direction U around a bed 320 and in an axial direction z along the bed 320. In the example shown, the manipulator unit 315 is annular and, in principle, is similar to a computed tomography scanner in terms of its structure and circumferential movement, but is axially movable, so that the magnetic field measuring unit 310 can be moved on a spiral path 350 around the bed 320 and a patient 330 serving as a measurement location.

[0034] The magnetic field detection device 300 (eg via its control unit) is configured to move the magnetic field measuring unit 310 by means of the movable manipulator unit 315 to at least two different positions (eg Figure 4 , P1, P1′ in the figure), and detecting the magnetic field strength and field direction at each of the at least two different positions. Signal processing unit 340 can determine at least one field vector including an effective magnetic field strength and an effective field direction based on the magnetic field strength and field direction detected at the at least two different positions.

[0035] In particular, a large number of measurements can be performed on the spiral track 350. The step size of the axial movement between two measurement positions can be selected, in particular, based on the resolution or image width of the magnetic field measurement unit 310 in the z-direction, in particular so that after one revolution, the z-position increases by at most one image width. Similarly, the circumferential step size between two measurement positions can be selected based on the resolution or image height of the magnetic field measurement unit 310 in the circumferential direction, in particular so that after each step, the u-position increases by at most one image height. In this way, a complete three-dimensional image of the magnetic field at the measurement location can be recorded. The magnetic field measurement unit 310 can be moved either alone or in conjunction with other detectors (e.g., X-ray detectors for CT imaging). The entire magnetic field detection device 300 can be magnetically shielded (e.g., by wall linings) or unshielded.

[0036] Figure 4 In a schematic diagram, a view of a plane in which a magnetic field measuring unit (eg 310) moves is schematically shown. Figure 3 The magnetic signal is measured in a magnetic field detection device. Figure 3 , which corresponds to a cross-sectional view perpendicular to the z direction, such as a view on the circle U.

[0037] The magnetic field 420 originating from an electrical conductor (eg, a nerve) with current flowing through it at the measurement location 330 is distributed in a circle around the measurement location 330, with the field strength indicated by 410. The background field (eg, the Earth's magnetic field) is indicated by 440.

[0038] For example, opposing measurements at positions P1 and P1 ′ can reduce magnetic noise: if the magnetic fields from positions P1 and P1 ′ are subtracted from each other, twice the amplitude of the circular signal field is obtained, while the ambient fields 440 of the same orientation cancel each other out.

Claims

1. A magnetic field detection device (300) for detecting a magnetic signal originating from a measurement location (330), comprising: A magnetic field measuring unit (310) with at least one NV magnetometer unit, the magnetic field measuring unit being connected to a signal processing unit (170, 340), wherein the magnetic field measuring unit (310) is arranged on a movable manipulator unit (315), The magnetic field detection device (300) is configured as follows: By means of the movable manipulator unit (315), the magnetic field measuring unit (310) is moved to at least two different positions (P1, P1') relative to the measurement location (330), and the magnetic field strength (410) and the field direction (420) are detected at each of the at least two different positions, and At least one field vector comprising an effective magnetic field strength and an effective field direction is determined by means of the signal processing unit (170, 340) based on the magnetic field strength (410) and the field direction (420) detected at the at least two different positions (P1, P1').

2. The magnetic field detection device (300) according to claim 1, wherein the magnetic field detection device (300) is configured to determine the effective magnetic field strength and the effective field direction based on the difference between the magnetic field strength (410) and the field direction (420) detected at the at least two different positions (P1, P1').

3. The magnetic field detection device (300) according to claim 1 or 2, wherein the at least two different positions (P1, P1') are equidistant from the measurement location (330) or from an axis passing through the measurement location.

4. The magnetic field detection device (300) according to any one of the preceding claims, wherein each two different positions of the at least two different positions (P1, P1') and the measurement location (330) or a point on an axis passing through the measurement location are located on a straight line.

5. The magnetic field detection device (300) according to any one of the preceding claims, wherein the magnetic field measurement unit (310) comprises at least two NV magnetometer units, and the NV magnetometer units are arranged in one plane (201).

6. A magnetic field detection device (300) according to any one of the preceding claims, wherein the at least one NV magnetometer cell has a diamond crystal or a portion of a diamond crystal with nitrogen-vacancy centers as a sensor medium (110; 210), wherein the magnetic field detection device (300) is configured to detect the magnetic field strength and the field direction by reading spin resonances in the sensor medium (110; 210) that are related to the magnetic field strength.

7. The magnetic field detection device (300) according to claim 6 further comprises at least one excitation light source (120) for injecting light (124) into the sensor medium (110; 210), at least one microwave source (150) for generating a resonance field in the sensor medium, and at least one photodetector (130) for detecting resonance-related fluorescence (112) from the sensor medium (110; 210).

8. The magnetic field detection device (300) according to claim 7, wherein the magnetic field measurement unit (310) comprises at least two NV magnetometer units, wherein the at least two NV magnetometer units are associated with the same excitation light source (120) and / or the same microwave source (150).

9. The magnetic field detection apparatus (300) according to any one of claims 6 to 8, further comprising at least one device (140) for generating a substantially uniform bias magnetic field at the location of the sensor medium (110; 210) of the at least one NV magnetometer unit.

10. The device according to any of the preceding claims, wherein the signal processing unit (170, 340) is configured to determine a plurality of field vectors respectively comprising a magnetic field strength and a field direction based on the magnetic field strength and field direction detected at the at least two different positions.

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