Magnetic field sensor

Abstract

The invention relates to a magnetic field sensor (1) with an NV diamond (3), an excitation light source (4) configured to emit excitation radiation (5) for exciting electronic states of the NV diamond (3), a microwave structure (6) configured to generate a microwave field for manipulating spin states of the NV diamond (3), a detector (11) configured to detect fluorescence radiation that the NV diamond (3) can emit as a result of irradiation with the excitation radiation (5), and a magnetic field generation device (8) arranged and configured to generate a permanent magnetic field in the region of the NV diamond (3), wherein the excitation light source (4), the microwave structure (6), and the magnetic field generation device (8) are arranged on a sensor board (2).

Description

The present invention relates to a magnetic field sensor based on an NV diamond.Prior ArtSo-called NV magnetic field sensors are used for detecting a magnetic field. These comprise a diamond whose crystal lattice has defects in the form of NV centers. In an NV center, a nitrogen atom occupies the lattice site of a carbon atom, wherein a defect is arranged in direct proximity to the nitrogen atom-again on the lattice site of a carbon atom. If such a crystal lattice is irradiated with excitation radiation having a wavelength between 490 nm and 575 nm, an electronic transition from a ground state 3 A 2 to an excited state 3 E is induced in the crystal lattice. From the excited state 3 E, the NV center relaxes again into the ground state 3 A 2. with emission of fluorescent radiation in a wavelength range between 600 nm and 850 nm. The ground state 3 A 2 has three magnetic substates with m s=0, m s= ±1. The states with m s=0 and m s= ±1 differ by an energy difference of 2.87 GHz (zero field splitting). If the NV center in the ground state 3 A 2 is now exposed to microwave radiation with a frequency of 2.87 GHz, the NV center oscillates between the m s=0,3 A 2- ground state and the m s= ±1, 3 A 2- ground state. When irradiated with the excitation radiation, the NV center is now partially shifted from the m s= ±1, 3 A 2- ground state into the excited m s= ±1, 3 E state. From there, it relaxes again to the basic state predominantly without radiation. If the amplitude of the fluorescent radiation is measured as a function of the frequency of the microwave radiation, then at a frequency of 2.87 GHz, a sudden drop in the amplitude of the fluorescent radiation (a so-called dip) results. The drop in the amplitude of the fluorescent radiation can be explained by the fact that--when microwave radiation having a frequency of 2.87 GHz is irradiated--the m s=0,3 A 2- ground state is less likely to be occupied.In an external magnetic field, the m s= ±1, 3 A 2- ground state splits into two states with the spin quantum number m s=1 and m s=-1 (Zeeman effect). If the amplitude of the fluorescent radiation is now measured by changing the frequency of the microwave radiation, two dips are obtained. The frequencies at which these dips occur depend on the magnitude of the splitting of the ms=±1, 3A2 ground state and thus on the field strength of the external magnetic field. In this way, the field strength of an external magnetic field can be determined.Such a magnetic field sensor is known, for example, from Xue Zhang (2021). Battery Characterization via Eddy-Current Imaging with Nitrogen-Vacuum Centers in Diamond. Appl. Sci., 11 (7), 3069. Herein, linearly polarized light of a green laser is injected into an NV diamond. Microwave radiation is generated by means of an RF coil, wherein the NV diamond is arranged within the turns of the RF coil. The fluorescent radiation emitted by the NV diamond is directed by means of a beam splitter onto two photodiodes, one of the two photodiodes acting as a reference detector, while the other of the two photodiodes is preceded by a filter which blocks the radiation of the green laser. The NV diamond is here bonded to the top plane of a parabolic concentrator. Such a magnetic field sensor requires space and is complicated to adjust.In the magnetic field sensors usually used in the prior art, the size of the field-generating components, in particular of the microwave source and of the magnetic field generating device, is selected such that the extent of the fields generated by them is so large that they have a sufficiently large homogeneous region. Further, in the related art, the NV diamond is surrounded by the microwave source, the magnetic field generating device, and the excitation light source in a three-dimensional structure, which results in difficult-to-adjust arrangements and impossible-to-automate manufacturing processes.It is an object of the invention to provide a magnetic field sensor which does not have the disadvantages of the prior art.Disclosure of the InventionThe present invention relates to a magnetic field sensor for detecting a magnetic field according to claim 1.In particular, the magnetic field sensor comprises an NV diamond, an excitation light source which is configured to emit excitation radiation for exciting electronic states of the NV diamond, a microwave structure which is configured to generate a microwave field for manipulating spin states of the NV diamond, a detector which is configured to detect fluorescent radiation which the NV diamond can emit as a result of irradiation with the excitation radiation, and a magnetic field generating device which is arranged and configured to generate a permanent magnetic field in the region of the NV diamond. In this case, the excitation light source, the microwave structure and the magnetic field generating device are arranged on a sensor printed circuit board, in particular in a single plane. This enables a simple production process which is automated and using standard tools, for example. Standard "Pick and Place Tools" can be run. Further, arranging the excitation light source, the microwave structure and the magnetic field generating device in a single plane allows a single mechanical reference to be used and thus a minimum tolerance between the different electromagnetic fields that can be generated by the excitation light source, the microwave structure and the magnetic field generating device can be maintained.In a further development of the invention, the magnetic field sensor can have a reference detector. This makes it possible to take into account the radiation which is detected by the reference detector during the evaluation of the signal detected at the detector. For example, the radiation which is detected at the reference detector can be subtracted as background radiation from the signal detected at the detector. The detector and / or reference detector can be designed as photodiodes.In a further development of the invention, the detector is arranged between the NV diamond and the sensor board. The detector can be directly adjacent to the NV diamond, for example glued to the NV diamond. Alternatively, a filter can also be arranged between the detector and the NV diamond, which filter is designed to block the excitation radiation. The reference detector may also be arranged on the sensor board. Such a construction is particularly easy to adjust.In a further development of the invention, the detector and / or the reference detector are arranged on a carrier plate opposite the sensor circuit board. The NV diamond emits the fluorescent radiation isotropically, i.e. in all directions with the same intensity. By providing the support plate opposite to the sensor board, fluorescent radiation emitted in a direction orthogonal to the direction of the excitation radiation can be detected. In this way, it is possible to dispense with a beam splitter which is designed to split the fluorescent radiation into two portions, wherein one of the two portions is directed towards the detector and the other of the two portions is directed towards the reference detector.Furthermore, the arrangement of the detector and / or the reference detector in the vicinity of the NV diamond enables a space-demanding focusing optics for collecting the fluorescent radiation, as used in the prior art, to be dispensed with. In particular, the detector is arranged in the immediate vicinity of the NV diamond, for example glued onto the NV diamond. An adhesive can be used here, the refractive index of which is matched to the refractive indices of the NV diamond and of the detector in order to avoid radiation losses during the transition of the fluorescent radiation from the NV diamond into the detector.Furthermore, an optical filter can be arranged between the detector and the NV diamond, which filter blocks the excitation radiation emitted by the excitation light source. In this way, the quality and quantity of the detected signal can be improved. The optical filter can be fastened directly to the detector, for example by spin coating (spin coating), or printed directly onto the detector (direct printing). The optical filter may be directly adjacent to the NV diamond on its opposite side.In a further development of the invention, a mirror prism is arranged in a light path of the excitation radiation between the reference detector and the NV diamond. The mirror prism is arranged and designed to direct the excitation radiation onto the reference detector. In this way, the intensity of the background radiation at the reference detector is increased, which leads to a higher sensitivity of the magnetic field sensor.In a development of the invention, an optical scattering element, in particular a volume scattering element, is arranged in the light path of the excitation radiation, between the NV diamond and the reference detector. The optical scattering element is designed in particular to scatter radiation with the wavelength of the excitation radiation before it strikes the reference detector. In this way, the sensitivity of the magnetic field sensor can be further improved.In a development of the invention, the excitation light source and the NV diamond are aligned with respect to one another such that the excitation radiation emitted by the excitation light source impinges on one of the side faces of the NV diamond at an angle of incidence of between 55° and 75°, in particular between 60° and 70°, particularly preferably between 63° and 68°. The NV diamond can be designed as polyhedron, for example as cube, cuboid or truncated pyramid with six side surfaces. The angle of incidence is defined as the angle between the solder on the side surface and the direction of incidence of the excitation radiation when it impinges on the side surface. The excitation radiation is in particular laser radiation. The angle of incidence thus selected is close to the Brookfield angle for an interface between air and diamond or corresponds to the Brookfield angle for an interface between air and diamond, so that in this way the polarized excitation radiation emitted by the excitation light source can be coupled into the volume of the NV diamond with a very high yield.In this case, the solder can be oriented onto one of the side surfaces of the NV diamond at an angle between 20° and 30°, in particular at an angle between 23° and 27°, with respect to the solder on field lines of the permanent magnetic field generated by the magnetic field generating device-as it is oriented within the NV diamond. The orientation of the field lines represents the orientation of the permanent magnetic field. In an alternative aspect, two of the edges delimiting a base surface of the NV diamond can be arranged at the above-mentioned angle between 20° and 30°, in particular between 23° and 27°, to the direction of the field lines of the permanent magnetic field. The base surface of the NV diamond is formed with two parallel side edges, for example, as a rectangle or square. The permanent magnetic field generated by the magnetic field generating device can have field lines running parallel to one another at least within the NV diamond, which lines run in particular parallel to the sensor board.In addition, the base surface of the NV diamond can be arranged tilted with respect to the plane of the sensor board, wherein the field lines of the permanent magnetic field run parallel to the plane of the sensor board. This tilting and the above-described non-parallel arrangement of the side surfaces of the NV diamond with respect to the field lines of the permanent magnetic field lead to an increased resolution of the detected signal.In a further development of the invention, the excitation radiation, the microwave field and the permanent magnetic field assume an angle of between 80° and 100°, in particular of 90°, with respect to one another within the NV diamond. In particular, the field lines of the permanent magnetic field, the field lines of the microwave field and the direction of the excitation radiation within the NV diamond assume an angle of between 80° and 100°, in particular of 90°, with respect to one another. Within a so-called active volume of the NV diamond, in which the permanent magnetic field, the microwave field and an optical field corresponding to the electromagnetic field of the excitation radiation overlap, the homogeneous regions of these fields can be optimally utilized due to the orthogonal or almost orthogonal arrangement of the fields. In this way, the components that generate these fields can be miniaturized.In a further development of the invention, the NV diamond, the excitation light source, the microwave structure, the detector and / or the reference detector are arranged in a closed space. The closed space can be hermetically sealed, in particular airtight, from the environment. This protects the excitation light source from dirt in particular. The arrangement of the other components of the magnetic field sensor, such as the NV diamond, the microwave structure and the detectors in addition to the excitation light source makes it possible to construct the magnetic field sensor in a compact manner.In a further development of the invention, the carrier plate is designed as a ceiling plate of the enclosed space. This also enables a very compact construction of the magnetic field sensor.In a development of the invention, at least one side face of the closed space is designed as a scattering element. In this case, the side face(s) are designed to diffusely scatter radiation having the wavelength of the excitation radiation, wherein the scattered radiation produced in this way impinges on the reference detector. Alternatively or additionally, a spacer can also be designed as a scattering element, which is arranged such that the excitation radiation transmitted through the NV diamond is diffusely scattered at the spacer.In a further development of the invention, the sensor circuit board forms a base plate of the enclosed space. In this case, the side surfaces and the ceiling plate of the enclosed space can be formed by a closure, in particular a one-piece closure. The carrier plate with the detector and / or the reference detector may be attached to the ceiling plate of the closure. Alternatively, the carrier plate can form the ceiling plate of the closure. In such an arrangement, the individual components of the magnetic field sensor are particularly simple to mount.In a development of the invention, the magnetic field generating device comprises an arrangement of permanent magnets. The permanent magnets can be arranged in a Halbach arrangement on the sensor board, so that the permanent magnetic field generated in the NV diamond is as homogeneous as possible. The permanent magnets can be configured as discrete individual magnets. Alternatively, a single ring magnet can also serve as a magnetic field generating device. In this case, only a part needs to be positioned relative to the position of the NV diamond, so that positioning of the magnetic field generating device is less complicated. Compared to a Helmholtz coil, the arrangement of permanent magnets has the advantage that a power supply can be dispensed with.Further advantages and embodiments of the invention will become apparent from the description and the accompanying drawing.The invention is schematically illustrated in the drawing on the basis of exemplary embodiments and is described below with reference to the drawing.Brief Description of the DrawingsFIG. 1 shows a magnetic field sensor according to a possible embodiment of the invention, comprising an NV diamond, an excitation light source, a magnetic field generating device and a microwave structure, wherein a detector and a reference detector are arranged on a carrier plate; FIG. 2 shows a magnetic field sensor according to a possible embodiment of the invention, wherein the detector and the reference detector are arranged on the carrier plate and a mirror prism is provided for deflecting excitation radiation onto the reference detector; FIG. 3 shows a magnetic field sensor according to a possible embodiment of the invention, wherein the detector and the reference detector are arranged on the carrier plate and a volume scattering element is provided for diverting excitation radiation onto the reference detector; FIG. 4 shows a magnetic field sensor according to a possible embodiment of the invention, wherein the detector and the reference detector are arranged on the carrier plate and a spacer is provided for diverting excitation radiation onto the reference detector; FIG. 5 shows a magnetic field sensor according to a possible embodiment of the invention, wherein the detector and the reference detector are arranged in a plane with the NV diamond, the excitation light source and the microwave structure; FIG. 6 shows a magnetic field sensor according to a possible embodiment of the invention, wherein the field lines of a permanent magnetic field generated by the magnetic field generating device and an excitation radiation generated by the excitation light source are shown in their mutual orientation within the NV diamond; FIG. 7 shows a magnetic field sensor according to a possible embodiment of the invention, wherein the field lines of the permanent magnetic field generated by the magnetic field generating device, a microwave field generated by the microwave structure and the excitation radiation are shown in their alignment with each other, as is present within the NV diamond.Embodiments of the InventionFIG. 1 shows a magnetic field sensor 1 having an NV diamond 3, a magnetic field generating device 8, a microwave structure 6 and an excitation light source 4. The wavelength of the excitation radiation 5 is in a range between 490 nm and 575 nm. The excitation light source 4 is arranged such that the NV diamond 3 is irradiated with the excitation radiation and electronic states of the NV diamond 3 can be excited. The NV diamond 3, the magnetic field generating device 8, the excitation light source 4 and the microwave structure 6 are arranged such that the electromagnetic fields that can be generated by the excitation light source 4, the microwave structure 6 and the magnetic field generating device 8 overlap with one another in the region of the NV diamond 3. In particular, the electromagnetic fields that can be generated by the excitation light source 4, the magnetic field generating device 8 and the microwave structure 6 are arranged in the same or in parallel planes.The microwave structure 6, the excitation light source 4, the magnetic field generating device 8, and the NV diamond 3 are disposed on a sensor board 2. In this case, for example, the excitation light source 4 can be arranged on an intermediate piece, which in turn can be arranged directly on the sensor printed circuit board 2. Furthermore, an optical element 7, for example a lens, can be provided, which focuses the excitation radiation 5 emitted by the excitation light source 4 onto the NV diamond 3.The magnetic field generating device 8 can be formed as an arrangement of permanent magnets which are arranged, for example, in a Halbach arrangement on the sensor printed circuit board 2, so that a permanent magnetic field is generated in a plane parallel to the sensor printed circuit board 2.On a support plate 9 disposed opposite and parallel to the sensor board 2, a detector 11 and a reference detector 10 are disposed. The detector 11 is arranged directly opposite the NV diamond 3 in particular, so that fluorescent radiation is detected at the detector 11 which has been emitted by the NV diamond 3 in a direction orthogonal to the light path of the excitation radiation 5. The reference detector 10 is configured to detect the background radiation generated by the excitation light source 4.The sensor board 2 may constitute the base plate of a sealed space, while the support plate 9 may constitute the ceiling plate of the sealed space.FIG. 2 shows the magnetic field sensor 1 from FIG. 1, wherein a mirror prism 12 is additionally provided, which is arranged in a beam path of the excitation radiation 5 between the reference detector 10 and the NV diamond 3. The mirror prism 12 reflects excitation radiation 5 such that it impinges on the reference detector 10.FIG. 3 likewise shows the magnetic field sensor 1 from FIG. 1, wherein a volume scattering element 13 is additionally arranged in the light path of the excitation radiation 5 between the reference detector 10 and the NV diamond. The volume scattering element 13 is designed to scatter the excitation radiation 5 in its volume, so that the excitation radiation 5 impinges on the reference detector 10 as scattered radiation 14.FIG. 4 likewise shows the magnetic field sensor 1 from FIG. 1, wherein the detector 11, the reference detector 10, the NV diamond 3, the microwave structure 6 and the excitation light source 4 are arranged in a closed space and a side wall of the closed space is configured to scatter the excitation radiation 5, such that the excitation radiation 5 impinges on the reference detector 10 as scattered radiation 14. Alternatively, a spacer 15 can also be arranged on the sensor board 2 and designed to scatter the excitation radiation 5 and direct it as scattered radiation 14 onto the reference detector 10.FIG. 5 shows an alternative embodiment of the magnetic field sensor 1. here the detector 11 and the reference detector 10 are likewise arranged on the sensor circuit board 2. The detector 11 is arranged between the sensor board 2 and the NV diamond 3, so that fluorescent radiation emitted from a bottom side of the NV diamond can be detected directly by the detector 11.FIG. 6 shows the NV diamond 3, the beam path of the excitation radiation 5 and field lines of the permanent magnetic field 16 generated by the magnetic field generating device. In the embodiment shown here, the angle of incidence α L of the excitation radiation 5 when incident on one of the side surfaces 18 of the NV diamond 3 is between 55° and 75°. The angle of incidence is defined as the angle between the solder 19 on the side face 18 of the NV diamond 3 and the beam path of the excitation radiation 5 when it impinges on the side face 18. The angle of incidence α L can be, for example, determined. 65°. The NV diamond is formed, for example, as a cuboid or cube. The angle α L selected in this way is close to the Brookfield angle or corresponds to the Brookfield angle of a diamond-air interface, so that the excitation radiation 5, in particular polarized excitation radiation, can be coupled into the NV diamond 3 with very high efficiency.Furthermore, the solder 19 on the side surface 18 of the NV diamond 3 can be tilted by an angle α D with respect to the solder 20 on the field lines of the permanent magnetic field 16 generated by the magnetic field generating device. The orientation of the field lines corresponds to the orientation of the permanent magnetic field 16. The angle α D can be, for example. 25°. The field lines of the permanent magnetic field 16 are oriented parallel to one another and in particular parallel to the plane of the sensor circuit board. The side surface 18 of the NV diamond is formed as a flat surface.In addition, a base surface of the NV diamond 3 can be arranged tilted with respect to the plane of the sensor board. The tilting of the NV diamond 3 in these two planes leads to an improved resolution of the signal.FIG. 7 shows the beam path of the excitation radiation 5, the field lines of the permanent magnetic field 16 and field lines of the microwave field 17 and the NV diamond 3. The field lines of the permanent magnetic field 16, the field lines of the microwave field 17 and the beam path of the excitation radiation 5 assume an angle of between 80° and 100°, in particular of 90°, with respect to one another within the NV diamond. The excitation radiation 5 is in particular designed as laser radiation and forms an optical field along its beam path. The field lines of the permanent magnetic field 16 are arranged within the NV diamond 3 parallel or almost parallel to one another. Likewise, the field lines of the microwave field 17 within the NV diamond 3 are arranged parallel or largely parallel to one another. Here, an area within the NV diamond 3 where the permanent magnetic field 16, the microwave field, and the optical field overlap each other is referred to as an active volume. Due to the orthogonal arrangement of the permanent magnetic field 16, the microwave field 17 and the optical field within the NV diamond 3, the homogeneous areas of the different fields in the active volume can be optimally utilized.References included in the specificationThis list of documents cited by the applicant has been produced in an automated manner and is only included for the better information of the reader. The list is not part of the German patent application or utility model application. The DPMA does not take any adhesion for any faults or omissions.Cited Non-Patent LiteratureXue Zhang (2021). Battery Characterization via Eddy-Current Imaging with Nitrogen-Vacuum Centers in Diamond. Appl. Sci., 11 (7), 3069

[0004]

Claims

Magnetic field sensor (1) having - an NV diamond (3), - an excitation light source (4) which is designed to emit excitation radiation (5) for exciting electronic states of the NV diamond (3), - a microwave structure (6) which is designed to generate a microwave field for manipulating spin states of the NV diamond (3), - a detector (11) which is designed to detect fluorescent radiation which the NV diamond (3) can emit as a result of irradiation with the excitation radiation (5), - a magnetic field generating device (8) which is arranged and designed to generate a permanent magnetic field in the region of the NV diamond (3), wherein the excitation light source (4), the microwave structure (6) and the magnetic field generating device (8) are arranged on a sensor board (2).Magnetic field sensor (1) according to claim 1, wherein the magnetic field sensor (1) comprises a reference detector (10).Magnetic field sensor (1) according to claim 1 or 2, wherein the detector (11) and / or the reference detector (10) is arranged on a carrier plate (9) opposite the sensor board (2).Magnetic field sensor (1) according to Claim 2 or 3, wherein a mirror prism (12) or an optical scattering element (13), in particular a volume scattering element, is arranged in a light path of the excitation radiation (5) between the reference detector (10) and the NV diamond (3).Magnetic field sensor (1) according to one of the preceding claims, wherein the excitation light source (4) is arranged such that the excitation radiation (5) emitted by it impinges on one of the side faces of the NV diamond (3) at an angle of incidence of between 55° and 75°.Magnetic field sensor (1) according to one of the preceding claims, wherein within the NV diamond (3) the excitation radiation (5), the microwave field and the permanent magnetic field assume an angle between 80° and 100°, in particular of 90°, with respect to one another.Magnetic field sensor (1) according to one of claims 3 to 5, wherein the NV diamond (3), the excitation light source (4), the microwave structure (6), the detector (11) and / or the reference detector (10) are arranged in a closed space.Magnetic field sensor (1) according to Claim 6, wherein the carrier plate (9) is designed as a ceiling plate and in particular the sensor printed circuit board (2) is designed as a base plate of the closed space.Magnetic field sensor (1) according to Claim 6 or 7, wherein at least one side face of the enclosed space is designed as a scattering element (15).Magnetic field sensor (1) according to one of the preceding claims, wherein the magnetic field generating device (8) comprises a permanent magnet or an arrangement of permanent magnets.

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