Sensor system for detecting a magnetic field or a measured variable associated with a magnetic field

Abstract

The present invention relates to a sensor system (1) for detecting magnetic field parameters of an external magnetic field, comprising an NV diamond (2), a microwave source (3), an excitation light source (4), at least one detector (6), and a magnetic field generating device (12). The microwave source is arranged and configured to generate a microwave field in the NV diamond (2), the excitation light source is arranged and configured to direct an excitation beam (5) toward the NV diamond (2), the detector is arranged and configured to detect the light signal emitted by the NV diamond (2) due to irradiation by the excitation beam (5), and the magnetic field generating device is arranged and configured to generate a detectable internal static magnetic field in the NV diamond (2). The sensor system (1) is characterized in that the magnetic field generating device (12) comprises a multilayer permanent magnet (7) arranged around the NV diamond (2).

Description

Technical Field

[0001] This invention relates to a sensor system for detecting magnetic fields or magnetic field-related measurement variables. Background Technology

[0002] To detect magnetic fields, so-called NV magnetic field sensors are used. These sensors consist of diamond, whose crystal lattice has defects in the form of NV centers. In an NV center, a nitrogen atom occupies a lattice position of a carbon atom, with a vacancy located directly adjacent to the nitrogen atom—also in a carbon lattice position. If such a lattice is irradiated with excitation radiation with wavelengths between 490 nm and 575 nm, an excitation from the ground state is induced in the lattice. 3 A2 to excited state 3 Electron transition of E. NV center from excited state 3 E relaxes back to the ground state under fluorescence radiation with emission wavelengths in the range of 600 nm to 850 nm. 3 A2. Ground state 3 A2 has three magnetic sublevels, m s= 0, m s= ±1. m s= 0 and m s= The ±1 states are distinguished by an energy difference of 2.87 GHz (zero-field splitting). Excited state 3 E also has three magnetic sublevels, m s= 0, m s= ±1. Under excitation radiation irradiation, the NV center portion originates from m s= ±1, 3 The A2 ground state transitions to the excited m state. s= ±1, 3 The E state. From there, it relaxes back to the m state primarily through a non-radiative and non-spin-preserving process. s= 0, 3 A2 ground state. Simultaneously, the excited m... s= 0, 3 The E state also relaxes to m under emitted fluorescence radiation. s= 0, 3 A2 ground state. If now the ground state... 3 If the NV center in A2 is exposed to microwave radiation at a frequency of 2.87 GHz, then the NV center at m s= 0, 3 A2 ground state and m s= ±1, 3Oscillations occur between the A2 ground state and the oscillations. If the amplitude of the fluorescence radiation is measured in relation to the microwave radiation frequency during irradiation with excitation radiation, a sudden drop in fluorescence radiation amplitude (the so-called "valley") occurs at 2.87 GHz. This drop in fluorescence radiation amplitude can be explained by the fact that irradiation with microwave radiation at a frequency of 2.87 GHz induces m... s= 0, 3 A2 ground state and m s= ±1, 3 The transition between the A2 ground states is spin-preserved excited by excitation radiation, but can relax back to m non-radiatively and non-spin-preserved. s= 0, 3 A2 ground state. Therefore, if irradiated with microwave radiation of the exact appropriate frequency, then m s= 0, 3 A2 ground state is cleared, while m s= ±1, 3 The A2 ground state is filled.

[0003] In a magnetic field, m s= ±1, 3 The A2 ground state splits into two quantum states with spin quantum number m. s= 1 and m s= The state of -1 (Zeeman effect). If we now measure the amplitude of the fluorescence radiation while changing the microwave radiation frequency, we will obtain two valleys. The frequencies at which these valleys appear depend on m. s= ±1, 3 The magnitude of the splitting of the A2 ground state, and therefore depends on the strength and direction of the magnetic field (especially its projection onto the corresponding NV axis). The projection of the magnetic field onto the NV axis can be obtained in this way.

[0004] Such NV magnetic field sensors are described, for example, in US 2019 / 0018091 A1. Furthermore, an internal static magnetic field is generated here by multiple permanent magnets, which are constructed as single magnets and arranged in a Halbach configuration comprising only a single layer. These single magnets are held by a frame fixed to a base. NV diamond is also mounted on this base. The single magnets are introduced into the frame along its perimeter, wherein the frame is oriented perpendicular to the base along its principal plane.

[0005] The sensitivity of the NV magnetic field sensor depends primarily on the uniformity of the internal static magnetic field at the NV diamond location. Typical field strengths range from 0.1 µT to tens of mT, with the uniformity of the internal static magnetic field measured within the volume of the NV magnetic field sensor typically less than 1000 ppm. The typical volume of the NV magnetic field sensor is 1 mm. 3Within a certain range. The internal static magnetic field is typically generated by a continuous current, a permanent magnet, or a combination of both. The uniformity of the generated internal static magnetic field directly depends on the size of the device generating it. In principle, to generate the most uniform magnetic field possible, the largest possible magnetic field generating device should be used, especially in systems with manufacturing tolerances. Therefore, a device is needed to generate the internal static magnetic field, which can be used in compact, robust, and sensitive NV magnetic field sensors.

[0006] To generate an internal static magnetic field, a conductor carrying a direct current, such as a loop current, solenoid, or Helmholtz coil, can be used. By using two concentric circular current loops arranged along the axis of symmetry at distances corresponding to the loop radii, fluctuations in the static magnetic field along the axis of symmetry can be compensated. Therefore, the Helmholtz coil configuration is the most common arrangement for generating a uniform static magnetic field using a continuous current.

[0007] Alternatively, permanent magnets can be used to generate a static magnetic field.

[0008] Furthermore, the two methods described above (the method using current-carrying conductors (Method 1) and the method using permanent magnets (Method 2)) can be combined. Alternatively, shimming techniques can be applied in conjunction with these two methods or one of them. Here, Method 1 and / or Method 2 are first used to generate a baseline level for the internal static magnetic field. Then, Method 1 and / or Method 2 are used to compensate for fluctuations in the static magnetic field within the target volume. For example, the static magnetic field can be generated by a permanent magnet arrangement (Method 2) and a relatively weak current-carrying conductor in a specific arrangement (Method 1). Here, the uniformity of the static magnetic field can be further improved by compensating for fluctuations in the static magnetic field within the target volume. This method, called "shimming," is a widely used tool for improving the uniformity of the generated static magnetic field. This method can be implemented passively, actively, or in a hybrid manner.

[0009] In passive compensation, field inhomogeneities are reduced by placing a small permanent magnet in a predefined location and / or inducing a predefined current into a coil placed in a predefined location. In active compensation, the position of the compensation permanent magnet and / or the current of the compensation (shimming) coil are matched with relevant characteristic numbers, such as the spectrum of detectable resonances, the total noise of the system, or the total sensitivity of the system. In hybrid compensation, there are several methods. For example, the position of the compensation permanent magnet is changed during assembly while the compensation current is turned off. The compensation current is then used to improve the performance coefficient.

[0010] The above method has a number of drawbacks. On the one hand, a magnetic field based on direct current requires a direct current power supply, which increases the power demand of the system. For example, for a static magnetic field of a few mT generated by a coil a few centimeters in size, the total current consumption may be as high as several hundred mW, making the component that generates the static magnetic field one of the biggest power consumers in the entire sensor system.

[0011] In addition, the heat generated by the coil or coil system With the current flowing through the wires that make up the coil It is proportional to the square of, that is ,in It is the total resistance of the conductor. The static magnetic field B0 generated by the coil and and the total number of windings in the system Proportional, for example .

[0012] However, it cannot be reduced and increase To completely reduce heat generation, because additional turns increase resistance. ,and And also related to the total length of the conductor Proportional to the cross-sectional area of ​​the conductor Inversely proportional, that is ,in This refers to the resistivity of the material. The heat generated by the current can also negatively affect permanent magnets used for shimming purposes or to generate the basic level of a static magnetic field. Furthermore, heat can induce temperature gradients in other parts of the permanent magnet or sensor, the effects of which on the system are unknown or very difficult to predict and / or compensate for.

[0013] Furthermore, the current required to generate a static magnetic field produces electronic noise from various sources, such as flicker noise and Johnson-Nyquist noise. This additional noise can negatively impact the system's noise floor, affect other components, and ultimately reduce system sensitivity.

[0014] The coils have high inductance, which allows them to couple with currents within the sensor housing, fields generated by other parts of the system, and external magnetic interference. This parasitic coupling can impair the sensitivity of the sensor system.

[0015] Furthermore, in the most common arrangement (Helmholtz coil), the static magnetic field generated by the current leads to a magnetic dipole moment. This results in significant stray fields outside the arrangement—from the outside, the arrangement itself appears as a permanent magnet. These stray fields enhance the parasitic effects of soft magnetic materials within the sensor system and in the immediate environment of the sensor. This parasitic magnetization of the surrounding structure can manifest as offset errors in measurements and compromise the uniformity of the static magnetic field B0 itself. Summary of the Invention

[0016] This invention relates to a sensor system for detecting an external magnetic field or a measurement variable related to an external magnetic field. Such a sensor system has a diamond (NV diamond) with at least one NV center. The sensor system also includes a microwave source, an excitation source, and a detector. The microwave source is arranged and configured to generate a microwave field in the NV diamond. The excitation source can be, for example, a diode laser. The excitation source is particularly configured to generate an excitation beam with a wavelength between 490 nm and 575 nm. The excitation source is also arranged and configured to direct the excitation beam towards the NV diamond, wherein the NV diamond emits an optical signal, particularly fluorescent radiation in the wavelength range of 600 nm to 850 nm, due to irradiation by the excitation beam. Here, optical elements for beam shaping (e.g., a lens) or beam guiding (e.g., a deflector) can be arranged between the excitation source and the NV diamond. The detector is constructed and arranged such that it can detect the optical signal emitted by the NV diamond due to irradiation by the excitation beam. In particular, the detector can be configured as a photodiode, which can detect radiation in the wavelength range of fluorescent radiation emitted by the NV diamond, particularly between 600 nm and 850 nm. Furthermore, at least one reference detector can be provided for detecting the excitation beam, enabling the determination of intensity fluctuations in the excitation source and the analysis and processing of the optical signal independent of these fluctuations. Optical filters, configured to filter out the wavelength range to be detected from their respective incident radiation, can be connected before the detector and / or the at least one reference detector.

[0017] The sensor system also includes a magnetic field generating device arranged and constructed to generate an internal static magnetic field within the NV diamond. This magnetic field generating device comprises a multi-layered, particularly two-layered, arrangement of permanent magnets surrounding the NV diamond. In the case of a two-layered permanent magnet arrangement, the NV diamond can be positioned between these two layers. These two layers are then spaced apart by a distance d, with the NV diamond, in particular, positioned at a distance of d / 2 from both layers. This arrangement generates a very uniform magnetic field within the NV diamond, thereby improving the measurement accuracy of the sensor system.

[0018] In one extended embodiment of the invention, the multilayer permanent magnet arrangement includes at least one, and particularly two, toroidal magnets, i.e., at least one, and particularly two, permanent magnets configured as toroidal magnets. Specifically, each layer may include exactly one toroidal magnet. The toroidal magnets may be arranged concentrically with each other. In the case where the permanent magnet arrangement includes exactly two layers, and therefore, specifically exactly two toroidal magnets, an NV diamond may be arranged in the middle between the two toroidal magnets, located on an axis passing through the centers of the two toroidal magnets. In this application, a toroidal magnet is understood to be a permanent magnet configured as a hollow cylinder whose magnetization direction changes continuously along its circumference; therefore, it is not a combination of single magnets.

[0019] In an extended embodiment of the invention, in at least one layer of a multilayer permanent magnet arrangement, at least two, and particularly four, permanent magnets are constructed as single magnets, wherein the magnetic dipole moments of adjacent single magnets point in different directions. The single magnets of each layer can be arranged in a plane, particularly along an imaginary circular line, thus creating a ring-shaped arrangement of permanent magnets, but not referred to as a ring magnet in this application. A single magnet can have a magnetic dipole moment, which is oriented, for example, along one of the edges of a cubic or cuboid single magnet.

[0020] The magnetization of a toroidal magnet, constructed as a hollow cylinder, can be oriented according to the Halbach arrangement. Here, the plane perpendicular to the principal axis of the toroidal magnet is defined as the xy-plane. When the magnetization of the toroidal magnet is oriented according to the Halbach arrangement, the magnetization is oriented in the xy-plane, especially along the principal axis (z-axis) of the toroidal magnet, where the magnetization is zero or close to zero. The direction of magnetization of the toroidal magnet here varies in the xy-plane, particularly at twice the pole angle (M∝(cos²2)). sin2 ,0)), where the polar angle Let M represent the angle in the xy plane, and M represent magnetization. Here, viewed in the circumferential direction, the magnitude of magnetization (Betrag) remains particularly constant, making the total magnetic dipole moment of the toroidal magnet zero. This creates a magnetic field in the xy plane.

[0021] In particular, the sensor system can have two layers, each with a toroidal magnet whose magnetization is oriented according to a Halbach arrangement. In this case, the two toroidal magnets are offset along the z-axis and arranged concentrically with each other. Here, the toroidal magnets in different layers have the same orientation in terms of magnetization in the xy-plane; that is, segments arranged on different toroidal magnets but with the same coordinates in the xy-plane, i.e., segments arranged directly above and below each other, have the same magnetization direction. In other words, when the two toroidal magnets are projected into the xy-plane, one toroidal magnet is imaged precisely or almost precisely on the other. In such an arrangement, the maximum magnetic field is generated inside the toroidal magnet arrangement, while the minimum magnetic field is generated outside the toroidal magnet arrangement.

[0022] A multilayer permanent magnet arrangement may have three or more individual magnets arranged according to the Halbach arrangement in at least one layer. The magnetic dipole moments of each individual magnet may have the same magnitude. The individual magnets are particularly arranged in a plane, preferably on an imaginary circular line, wherein the orientation of each magnetic dipole moment varies, in particular, with a change in direction at twice the pole angle (m∝(cos²2)). sin2 Here, the total dipole moment m of each layer is especially equal to zero ( ,0)). ), where m i This represents the magnetic dipole moment of each individual magnet. This arrangement has the advantage that components in a Halbach arrangement environment are not magnetized or are only weakly magnetized, thus reducing the sensitivity of the sensor system.

[0023] The magnetic field generating device of the sensor system has, in particular, two layers, in each layer arranging three or more individual magnets, specifically according to a Halbach arrangement. The two layers are concentrically arranged, with the individual magnets arranged circularly in each layer. The individual magnets in each layer are arranged vertically in the z-direction; that is, individual magnets with the same magnetic dipole moment orientation in the xy-plane have the same coordinates in the xy-plane, but different coordinates in the z-direction. Therefore, the magnetic dipole moments of the vertically arranged individual magnets point in the same direction. Here, the largest internal static magnetic field is generated inside the two-layer arrangement, while the smallest is generated outside. The uniformity of the internal static magnetic field depends particularly on the distance between the two layers in the z-direction. The optimal distance for maximizing the uniformity of the internal static magnetic field can be determined through a simulation optimization process.

[0024] The Halbach arrangement of the aforementioned single or toroidal magnets does not have rotational symmetry with respect to the z-axis.

[0025] In an extended embodiment of the invention, the multilayer arrangement has at least two permanent magnets arranged around an NV diamond as an Aubert arrangement. Here, in particular, the magnetization and / or magnetic dipole moment of the permanent magnets are oriented according to the Aubert arrangement.

[0026] In such an arrangement, at least one layer may have a permanent magnet constructed as a toroidal magnet, the magnetization direction of which changes continuously in the xy plane at a single pole angle. Here, viewed in the circumferential direction, the magnitude of magnetization remains particularly constant, making the total dipole moment of each toroidal magnet zero. () or close to zero. In particular, toroidal magnets have little or no magnetization in the z-direction.

[0027] In particular, the magnetic field generating device of the sensor system has two layers, each with a ring magnet. The magnetization direction of the first ring magnet in the first layer points outward when viewed from the center of the ring, while the magnetization direction of the second ring magnet in the second layer points inward when viewed from the center of the ring. The magnetization direction varies by a single pole angle in each layer. Using a magnetic field generating device constructed in this way for the Aubert arrangement, a very uniform magnetic field is obtained in the volume surrounding the center of the arrangement. The internal static magnetic field is oriented along the z-axis of two concentrically arranged toroidal magnets. In particular, the magnitude of magnetization remains constant when viewed in the circumferential direction of the toroidal magnets, making the total dipole moment of each toroidal magnet zero. The uniformity of the internal static magnetic field is either zero or close to zero. These two toroidal magnets preferably have the same outer radius. Here, the uniformity of the internal static magnetic field depends particularly on the distance between the two layers in the z-direction. The optimal distance for maximizing the uniformity of the internal static magnetic field can be determined through a simulation optimization process.

[0028] If the toroidal magnets are made of materials with different magnetization intensities, they can also have different radii. In this case, the toroidal magnet made of a weaker magnetizing material has a smaller outer radius, resulting in an internal static magnetic field that is as strong as if the two toroidal magnets were made of materials with the same magnetization intensities and had the same radius.

[0029] In one extended embodiment of the invention, at least one layer of the magnetic field generating device has at least two, in particular three or more, individual magnets, wherein an Aubert arrangement is derived for the entire magnetic field generating device.

[0030] In particular, the magnetic field generating device has two layers of permanent magnets constructed as single magnets, arranged in an Aubert arrangement. The single magnets can be arranged along an imaginary circular line in each of the two layers, wherein the circles defined by these two circular lines can be arranged concentrically. Here, the z-axis specifically passes through the center of these two circles.

[0031] In particular, a single magnet within a layer is positioned according to its polar angle. Arrangement, among which It refers to the number of individual magnets in the first layer. It refers to the number of individual magnets in the second layer. This represents the corresponding single magnet. The orientation of the magnetic dipole moment of a single magnet in the xy plane varies by a single pole angle from one single magnet to the next. The magnetic dipole moments of each individual magnet are zero or close to zero in the z-direction. Here, the magnetic dipole moments of the individual magnets in the first layer point outwards when viewed from the center of the imaginary circle, while the dipole moments of the individual magnets in the second layer point inwards, i.e., towards the center of the circle. This results in the formation of an internal static magnetic field along the z-axis. This internal static magnetic field is thus very uniform in the volume surrounding the center of the magnetic field generating device, which is the point on the z-axis located at half the distance between the two layers. Here, as in the other two-layer arrangement, the uniformity of the internal static magnetic field depends particularly on the distance between the two layers in the z-direction. The optimal distance for maximizing the uniformity of the internal static magnetic field can be determined through a simulation optimization process.

[0032] The magnitudes of the magnetic dipole moments of individual magnets can be the same. In this case, the individual magnets in each layer are arranged along the same imaginary circular line. This results in a total dipole moment of zero in each layer. ).

[0033] In particular, the number of individual magnets in each layer can also be the same. Furthermore, the individual magnets in the two layers can be arranged on the same imaginary circular line, where the magnetic dipole moments of the individual magnets in each layer are the same, and the centers of the two circles thus formed are located on the z-axis. The configuration of the Aubert arrangement just described therefore has discrete rotational symmetry with respect to the z-axis; that is, rotating the arrangement by an angle of 360° / n will cause the arrangement to map onto itself. In such a symmetrical arrangement, each individual magnet experiences the same magnetic field, such that all individual magnets are magnetized or demagnetized to the same degree by their neighboring magnets. This results in no loss of uniformity due to this effect, even if non-zero magnetization or demagnetization occurs.

[0034] In an extended embodiment of the invention, the permanent magnet is constructed as a single magnet and arranged in an Aubert arrangement with at least two layers, wherein the single magnets of the first layer are arranged offset from the single magnets of the second layer, such that the first layer can be described as "twisted" relative to the second layer, particularly at an arbitrary angle. The single magnets of each layer are arranged along imaginary circular lines, wherein the circles defined by these imaginary circular lines have the same radius and are arranged concentrically with each other. Thus, an arrangement is obtained in which the single magnets of adjacent layers are not directly vertically arranged when viewed in the z-direction. Such an arrangement allows for flexible arrangement of other components of the sensor system. It has been shown that the angle of twist between the two layers has little or no effect on the uniformity of the magnetic field and therefore on the sensitivity of the sensor system.

[0035] The first layer may, alternatively or additionally, differ from the second layer in the number of individual magnets. Specifically, the sum of the dipole moments of the individual magnets in the first layer is equal to the sum of the dipole moments of the individual magnets in the second layer; that is, if the magnetic dipole moments of all individual magnets in a layer have the same magnitude m, then n1m1 = n2m2 applies. The total magnetic dipole moment of each layer... and Here it equals 0. This represents the corresponding magnetic dipole moment of the single magnet 9 in the first layer. The first layer represents the magnetic dipole moment of a single magnet in the second layer. n1 and n2 represent the number of single magnets in the first and second layers, respectively. This arrangement allows other components of the sensor system, such as the excitation light source and / or microwave source, to be arranged in a space-saving manner. However, this does not, or barely, compromise the sensitivity of the sensor system. In this way, the sensor system can be constructed to be compact.

[0036] Compared to the Halbach arrangement, the Aubert arrangement offers several advantages: Individual magnets can be arranged more flexibly, allowing for greater freedom in the arrangement of other components in the sensor system. Comparing a two-layer Halbach arrangement with a two-layer Aubert arrangement that produces the same number of individual magnets per layer and the same radius, generating the same internal static magnetic field (i.e., the same target magnetic field), the Aubert arrangement requires individual magnets with dipole moments approximately 55% larger than those in the Halbach arrangement. This offers several advantages. Firstly, with the same target magnetic field and individual magnets arranged at the same radius as in the corresponding Halbach arrangement, the Aubert arrangement can utilize individual magnets with larger dipole moments, thus incorporating materials with stronger magnetization and coercivity, making them less prone to demagnetization. Secondly, with the same target magnetic field, radius, and individual magnet material, the Aubert arrangement can use individual magnets with larger dipole moments, allowing for larger external dimensions. These advantages are easier to manage during sensor system assembly and less sensitive to manufacturing tolerances.

[0037] Compared to the Halbach arrangement with the same radius and the same number of individual magnets, the magnetic field generated by the Aubert arrangement is more uniform. Furthermore, the Aubert arrangement is less sensitive to the position of the permanent magnets used, as well as the magnitude and orientation of their magnetic dipole moments.

[0038] In an extended embodiment of the invention, single magnets in a layer arranged according to an Aubert or Halbach arrangement are arranged along at least two distinct imaginary circular lines that define concentrically arranged circles, i.e., circles with different radii around a common center. For example, one single magnet may be arranged on a first circular line, and the remaining single magnets on a second circular line. Thus, at least one single magnet is arranged on a different radius than the others. The single magnets arranged on different circular lines have their own different magnetic dipole moments, wherein the single magnet with a larger magnetic dipole moment has a larger radius than the single magnet with a smaller magnetic dipole moment. In particular, half or more of the single magnets may differ from each other in their magnetic dipole moment magnitude and their radius. It is understood that the radius is directly related to the distance of the single magnet from the NV diamond arranged at the center of the magnetic field generating device; that is, the larger the radius, the greater the distance from each single magnet to the NV diamond.

[0039] Assuming the magnitude of the magnetic dipole moment of each individual magnet is known, this arrangement allows the use of individual magnets whose dipole moment magnitude deviates from the target value, while still generating a uniform internal static magnetic field.

[0040] A single magnet may alternatively or additionally have a magnetic dipole moment oriented not in accordance with its respective geometric orientation. For example, the magnetic dipole moment of a cubic or cuboid single magnet may be oriented at an angle between 0° and 90° relative to at least one edge of the cubic or cuboid single magnet. Similarly, the magnetic dipole moment of a cylindrical single magnet may be oriented at an angle between 0° and 90° relative to the principal axis of the cylindrical single magnet, i.e., the geometric orientation deviates from the orientation of the magnetic dipole moment.

[0041] Such a single magnet can be geometrically oriented in a Halbach or Aubert arrangement such that its magnetic dipole moment is oriented according to its pre-given orientation in the Halbach or Aubert arrangement, i.e., in the case of the Aubert arrangement, the magnetic dipole moment points to the center of the circle, the single magnet under consideration is arranged along the circular line of the circle, and the edges or principal axes of the single magnet do not point to the center of the circle.

[0042] Assuming that the direction of the magnetic dipole moment of a single magnet can be precisely measured, then inexpensive single magnets whose magnitude and direction of magnetic dipole moment are not precisely specified by the manufacturer can still generate a very uniform magnetic field within the arrangement.

[0043] A single magnet can be constructed in the shape of a cube, cylinder, or cuboid, especially with edge lengths between 0.1 mm and 5 mm.

[0044] Especially in an arrangement where the radius of a single magnet is about 5 mm, it may be advantageous if the single magnets have the same aspect ratio, i.e., constructed as a cube, or—if they are constructed as cylinders—with equal or approximately equal height and diameter.

[0045] Single magnets can also be arranged on one or more circular lines, defining circles with radii between 2 mm and 200 mm, particularly between 5 mm and 50 mm. This results in the distances between each single magnet and the NV diamond arranged at the center of the magnetic field generating device being within a similar dimensional range. A magnetic field generating device with single magnets arranged in an Aubert arrangement within these radii produces a very uniform magnetic field and is less sensitive to deviations between actual and assumed positions, as well as deviations in the actual magnetic dipole moment magnitude and orientation from assumed values, in terms of the uniformity of the generated magnetic field. An Aubert arrangement with as many single magnets as possible also has the same advantages. Attached Figure Description

[0046] Figure 1 A schematic structure of a sensor system according to one embodiment of the present invention is shown.

[0047] Figure 2 The magnetic field generating device in which the single magnets are arranged in a Halbach arrangement is shown.

[0048] Figure 3 A magnetic field generating device with a total of eight single magnets arranged in a Halbach arrangement is shown.

[0049] Figure 4 The magnetic field generating device in which the single magnets are arranged in an Aubert arrangement is shown.

[0050] Figure 5 This illustrates a magnetic field generating device in which cubic single magnets are arranged in an Aubert arrangement.

[0051] Figure 6 The magnetic field generating device is shown in which the rectangular single magnets are arranged in an Aubert arrangement.

[0052] Figure 7 a) through c) illustrate magnetic field generating devices in which single magnets are arranged in a Halbach configuration with different radii or different orientations of their respective magnetic dipole moments. For clarity, only one layer is shown.

[0053] Figure 8 A magnetic field generating device is shown in which the single magnets are arranged in an Aubert arrangement, wherein the single magnets in two layers are arranged at an angle α offset from each other.

[0054] Figure 9 a) to c) respectively illustrate magnetic field generating devices in which the single magnets are arranged in an Aubert arrangement, wherein... Figure 9 In b), the single magnets of the two layers are arranged at a certain angle and staggered from each other. Figure 9 In c), the number of individual magnets in the first layer is additionally different from the number of individual magnets in the second layer. Detailed Implementation

[0055] Figure 1An overview of a sensor system 1 for detecting magnetic field parameters of an external magnetic field is shown. The sensor system 1 includes a diamond crystal with NV defects (NV diamond 2), a microwave source 3, an excitation source 4, at least one detector 6, at least one reference detector (not shown here), and a magnetic field generating device 12. Optical filters (not shown here) can be arranged at the detector 6 and / or the reference detector, respectively configured to block wavelength ranges that should not or cannot be detected by the detector 6 and / or the reference detector. The detector 6 and / or the reference detector can be configured as photodiodes. The excitation source 4 is configured to emit an excitation beam 5. The wavelength of the excitation beam 5 is particularly in the range of 490 nm to 575 nm. The NV diamond 2 and the excitation source 4 are arranged such that the NV diamond 2 can be irradiated by the excitation beam 5. Here, the excitation beam 5 can be guided onto the NV diamond 2, for example, via a partial reflector, wherein the reflective portion of the excitation beam 5 can be guided onto the NV diamond 2, and the transmissive portion of the excitation beam 5 can be guided onto the reference detector. Microwave source 3 is configured to emit microwave radiation 13 and arranged such that the emitted microwave radiation 13 generates a microwave field in NV diamond 2. Detector 6 is configured to detect fluorescence radiation, for example, in the wavelength range between 600 nm and 850 nm, and is configured, for example, as a photodiode. Detector 6 can be directly mounted on one side surface of NV diamond 2. Optionally, a filter can be arranged between NV diamond 2 and detector 6, the filter being configured to separate fluorescence radiation from the excitation beam. Multiple detectors, particularly multiple photodiodes, can also be arranged to detect only fluorescence radiation or simultaneously detect fluorescence radiation and excitation beam 5. Optionally, filters can be connected before the at least one detector 6 and / or the at least one reference detector, these filters filtering out a predetermined wavelength range from the incident radiation. Magnetic field generating device 12 is configured and arranged to generate a static internal magnetic field B in NV diamond 2. Magnetic field generating device 12 can have two layers of at least two permanent magnets 7 arranged such that NV diamond 2 is arranged at the center of magnetic field generating device 12. The permanent magnets 7 can be—as Figure 1 As shown, it is constructed as a single magnet 9 or as a ring magnet with a continuously changing magnetization direction.

[0056] Figure 2 A magnetic field generating device 12 according to an embodiment of the present invention is shown, wherein the permanent magnets are constructed as single magnets 9. Twelve single magnets 9 are arranged according to a Halbach arrangement 10 in a first layer 14 and a second layer 16, respectively. The magnetic dipole moments of the single magnets 9 typically have the same magnitude.

[0057] Permanent magnets can also be constructed as toroidal magnets. In this case, the magnetization (viewed along the circumference of the toroidal magnet) has the same magnitude. The magnetic dipole moment and magnetization are related by the formula... Related. Where m represents the magnetic dipole moment of a single magnet, M represents magnetization, and V represents the volume of a single magnet.

[0058] In order to generate a magnetic field with a specific magnetic flux density, toroidal magnets must have a much larger volume than single magnets, while they can be made of materials with lower magnetization than the corresponding single magnets.

[0059] Single magnets 9 in one layer are arranged in a single plane along circular lines 15 and 25 defined by a circle of radius R. The magnetic dipole moment m of a single magnet 9 is... i The direction (or the magnetization direction in the case of a toroidal magnet) varies along the circumference at twice the pole angle. The polar angle is an angle in the xy-plane, which represents the plane in which the single magnet 9 is arranged. When the permanent magnet is a toroidal magnet, the xy-plane is a toroidal plane. The z-component of the magnetic dipole moment of the single magnet 9 or the magnetization of the toroidal magnet is zero or nearly zero here.

[0060] In this arrangement, a static magnetic field is generated inside the toroidal magnet or within the toroidal arrangement of the single magnet 9. Outside the toroidal magnet or the toroidal arrangement of the single magnet 9, the static magnetic field disappears.

[0061] The first and second layers are arranged concentrically and offset from each other by a distance d along the z-axis. The magnetic dipole moments of the single magnets 9 arranged directly above and below point in the same direction. The uniformity of the resulting internal static magnetic field is at the center of the arrangement. The largest of the surrounding volumes, of which It is the origin of the coordinate system. The arrangement center is located on the z-axis, at a distance of d / 2 from the two layers. The z-axis passes through the center of the circle defined by circular lines 15 and 25, and the single magnets of the first and second layers are arranged on these circular lines. The resulting magnetic field B extends in the xy plane. NV Diamond— Figure 1 Not shown in the image—located at the center of the magnetic field generating device. The above description similarly applies to cases where the permanent magnet is constructed as a toroidal magnet.

[0062] exist Figure 3 In the magnetic field generating device, a total of eight single magnets 9 are arranged in two layers, with each layer comprising four single magnets. These four single magnets 9 are arranged along imaginary circular lines 15 and 25 according to the Halbach arrangement 10. Spacers are arranged between directly adjacent single magnets 9 in each layer, and the spacers are made of non-magnetic material.

[0063] To ensure that the total dipole moment m of each layer is zero ( Each Halbach arrangement can have more than three single magnets or exactly three single magnets.

[0064] In a magnetic field generating device with two ring magnets, this condition is satisfied if the absolute value of magnetization, i.e., its magnitude, does not change along the circumference.

[0065] Figure 4 A magnetic field generating device 12 is shown, in which single magnets 9 are arranged in an Aubert arrangement 11. Similarly, the magnetic field generating device 12 has two layers 14, 16, in each layer, where single magnets 9 are arranged along imaginary circular lines 15, 25. The two layers 14, 16 are concentric and offset from each other along the z-axis. Each single magnet 9 in the first layer 14 has a magnetic dipole moment that points outwards when viewed from the center of the circle defined by the first imaginary circular line 15; that is, the direction of the magnetic dipole moment of the single magnet 9 in the xy-plane varies with a single pole angle. The z-component of the magnetic dipole moment is zero or almost zero here.

[0066] The individual magnets in the second layer 16 each have a magnetic dipole moment, which points inward when viewed from the center of the circle defined by the second imaginary circular line 25. That is, similarly, the direction of the magnetic dipole moment of the individual magnet 9 in the xy plane varies with a single polar angle. The uniformity of the generated internal static magnetic field is at the arrangement center and the origin of the coordinate system. It is the largest in the surrounding volume. It is also equipped with [something else]. Figure 3 NV diamond is not shown. Therefore, the resulting magnetic field B is oriented along the z-axis.

[0067] To ensure that the total dipole moment m of each layer is zero ( Each Aubert arrangement can have more than two single magnets or exactly two single magnets.

[0068] Alternatively, concentric ring magnets offset along the z-axis can be constructed as an Aubert arrangement. In this case, one of the two ring magnets is magnetized outwards, and the other is magnetized inwards. If the absolute value of the magnetization, i.e., its magnitude, does not change along the circumference, then the condition that the total dipole moment m of each layer is zero is satisfied.

[0069] Figure 5 A magnetic field generating device 12 with single magnets 9 arranged in an Aubert arrangement 11 is shown. The magnetic dipole moments of the single magnets 9, arranged along an imaginary circular line 15, point towards the center 17 of the circle defined by the circular line 15 in the first layer 14, and point outwards when viewed from the center 17 in the second layer 16. Each of these two layers comprises four single magnets 9. The single magnets 9 are here constructed in a cubic shape.

[0070] Figure 6 It was shown again Figure 5 The magnetic field generating device 12 in the middle, but the single magnet 9 has a rectangular shape.

[0071] Figure 7 a) through c) show three different arrangements of the single magnet 9 in a corresponding layer of the magnetic field generating device 12 constructed as a Halbach arrangement 10 in this case. Alternatively, the single magnet 9 can also be arranged as an Aubert arrangement. Figure 7 a) shows the target location of a single magnet 9 in a layer of the Halbach arrangement. All single magnets 9 have the same magnetic dipole moment (white arrow), which is parallel to the geometric orientation of the individual single magnet. In this case, the single magnets are constructed as cuboids. The magnetic dipole moment of each single magnet is correspondingly parallel to the long edge of the cuboid. This corresponds to the ideal case. All single magnets are positioned on a circle of radius r0. Figure 7 (b) illustrates how a single magnet will be positioned when the magnitude of the magnetic dipole moment deviates from the target value. A single magnet with a larger magnetic dipole moment is positioned at a larger radius r. + On r0, for example, a single magnet 19 at a radius r + Above. A single magnet with a small magnetic dipole moment, such as a single magnet 20, is positioned at a small radius r. - superior. Figure 7 c) illustrates how a single magnet is positioned when the orientation of the magnetic dipole moments deviates from their respective geometries. As an example, the single magnet 20 is slightly rotated so that its magnetization is directed in the desired direction (corresponding to...). Figure 7 (target value in a)).

[0072] Figure 8 A magnetic field generating device 12 with single magnets 9 arranged in an Aubert arrangement is shown. The single magnets 9 are arranged along imaginary circular lines 15 and 25 around the center of a circle defined by the imaginary circular lines 15 and 25, respectively. As is typical for an Aubert arrangement, the magnetic dipole moments of the single magnets 9 in the first layer 14 point away from the center of the circle, while the magnetic dipole moments of the single magnets 9 in the second layer 16 point towards the center. However, unlike the magnetic field generating device 12 previously shown, the two layers 14 and 16 are arranged at an angle α to each other in the xy plane. Therefore, the single magnets 9 in the first layer 14 are not congruent to the single magnets 9 in the second layer 16 when viewed in the z-direction, but differ in their x and y coordinates.

[0073] Figure 9 a) through c) show projections along the z-axis onto a magnetic field generating device configured as an Aubert. Figure 9 a) shows the case where the single magnets 9 of the first and second layers are arranged directly above and below each other. Figure 9 b) shows a twisted arrangement in which the single magnet 9a of the first layer 14 has different coordinates in the xy plane than the single magnet 9b of the second layer 16.

[0074] exist Figure 9 In a) and 9b), the two layers 14 and 16 have the same number of individual magnets 9.

[0075] Figure 9 c) also shows such a torsional arrangement, but the two layers 14 and 16 additionally differ in the number of their individual magnets 9. Here, in particular, the sum of the magnetic dipole moments of each individual magnet in each layer is equal; that is, if the magnetic dipole moments of all individual magnets in a layer have the same magnitude m, then n1m1 = n2m2 applies. The total magnetic dipole moment of each layer... and Here it equals 0. This represents the corresponding magnetic dipole moment of the single magnet 9 in the first layer. This represents the corresponding magnetic dipole moment of a single magnet in the second layer. n1 and n2 represent the number of single magnets in the first and second layers, respectively. Therefore, for a layer with a large number of single magnets, single magnets with smaller magnetic dipole moments can be used. For example, if n1 single magnets with a magnetic dipole moment of m are arranged in the first layer, then n2 = 2n1 single magnets with a magnetic dipole moment of m / 2 can be arranged in the second layer.

Claims

1. A sensor system (1) for detecting magnetic field parameters of an external magnetic field, comprising: NV diamond (2) A microwave source (3) is arranged and constructed to generate a microwave field in the NV diamond (2). Excitation light source (4), which is arranged and constructed to direct the excitation beam (5) toward the NV diamond (2). At least one detector (6), said at least one detector being arranged and configured to detect the light signal emitted by said NV diamond (2) due to irradiation by said excitation beam (5), A magnetic field generating device (12) is arranged and constructed to generate a static magnetic field that can be detected inside the NV diamond (2). Its features are, The magnetic field generating device (12) includes a multilayer permanent magnet (7) arranged around the NV diamond (2).

2. The sensor system (1) according to claim 1, wherein, The multilayer permanent magnet (7) is arranged with at least one, especially two, annular magnets, wherein the magnetization direction of the at least one annular magnet changes continuously along the circumference of the annular circle.

3. The sensor system (1) according to claim 1 or 2, wherein, The multilayer permanent magnet (7) is arranged in at least one layer having at least two, especially four, single magnets (9) with non-zero magnetic dipole moments, wherein the magnetic dipole moments of directly adjacent single magnets (9) point in different directions.

4. The sensor system (1) according to any one of the preceding claims, wherein, Two or more permanent magnets (7) are arranged around the NV diamond according to the Halbach arrangement (11).

5. The sensor system (1) according to any one of the preceding claims, wherein, Two or more permanent magnets (7) are arranged around the NV diamond according to the Aubert arrangement (11).

6. The sensor system (1) according to claim 5, wherein, The first layer of single magnets (9) is arranged in a twisted manner relative to the second layer of single magnets (9).

7. The sensor system (1) according to any one of claims 3 to 6, wherein, The first layer of single magnets (9) has a different number of single magnets (9) than the second layer of single magnets (9), wherein the sum of the magnitudes of the magnetic dipole moments of each layer is equal.

8. The sensor system (1) according to any one of claims 3 to 7, wherein, In the single magnets (9) in the same layer, at least one single magnet (9) is different from the other single magnets (9) in terms of the magnitude of its magnetic dipole moment and its distance from the NV diamond (2).

9. The sensor system (1) according to any one of claims 3 to 8, wherein, At least one of the single magnets (9) has a magnetic dipole moment that extends at an angle between 0° and 90° relative to at least one of the principal axes of the cylindrical, cubic or cuboid single magnet (9).

10. The sensor system (1) according to any one of the preceding claims, wherein, The permanent magnet (7) is constructed as a cubic or cuboid single magnet (9), especially having an edge length between 0.5 mm and 5 mm.

11. The sensor system (1) according to any one of the preceding claims, wherein, The permanent magnet (7) is constructed as a single magnet (9) and is arranged at a distance of 2 mm to 200 mm from the NV diamond (2), especially 5 mm to 50 mm.

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