Sensor unit for measuring magnetic fields

Abstract

The invention relates to a sensor unit for measuring magnetic fields, comprising: a magnetometer comprising at least one sensor medium and a flux concentrator, which is configured to concentrate an external magnetic field, in particular the Earth's magnetic field, at at least one location in the at least one sensor medium, independently of a rotation of the at least one sensor medium about at least one axis of rotation defined by a shape of the flux concentrator.

Description

The invention relates to a sensor unit for measuring magnetic fields. State of the art Various sensor technologies are known for measuring very low magnetic field strengths. One of the most sensitive sensor types is the SQUID magnetometer (Superconducting Quantum Interference Device), which is based on superconducting components and can resolve individual magnetic flux quanta or fields down to the range of a few picotesla (pT). However, a disadvantage of SQUID sensors is the need for cooling below the superconducting transition temperature, which for most superconducting materials is below 63 Kelvin, i.e., below the temperature of liquid nitrogen. Furthermore, the measuring range of these sensors is limited and they cannot operate in strong interfering fields, meaning that measurements are only possible in specially magnetically shielded environments. Similarly, quantum-based magnetic sensors based on nitrogen vacancy centers, which rely on the detection of spin resonances in magnetic fields, are known, for example, from DE 10 2018 220 234 A1 or DE 10 2018 214 617 A1. Patent US 10,705,163 B2 discloses a magnetic field sensor. The patent application DE 10 2020 119 414 A1 discloses a quantum sensor. Disclosure of the invention The object underlying the invention is to provide a concept for measuring magnetic fields. This problem is solved by means of the subject matter of the independent claim. Advantageous embodiments of the invention are the subject of dependent dependent claims. According to one aspect, a sensor unit for measuring magnetic fields is provided, comprising: a magnetometer comprising at least one sensor medium and a flux concentrator, which is configured to concentrate an external magnetic field, in particular Earth's magnetic field, at at least one location in the sensor medium, independently of a rotation of the at least one sensor medium about at least one axis of rotation defined by a shape of the flux concentrator. This results, for example, in the technical advantage that the external magnetic field can be efficiently concentrated at at least one location within at least one sensor medium. In particular, this provides the technical advantage that this concentration occurs independently of rotation around a defined axis. Therefore, the sensor unit can be used for mobile applications where a specific, fixed position of the sensor unit cannot always be guaranteed. This results in the particular technical advantage that a magnetic field can be measured efficiently. In one embodiment of the sensor unit, the shape of the flow concentrator comprises at least one element selected from the following group of shapes: disc segment, truncated disc segment, at least a part, in particular half, of a spiral torus, a helix shape wound around at least a segment of a circle, in particular a full circle, three-quarter circle or semicircle, or ellipse, in particular a half-ellipse, three-quarter ellipse or full ellipse, triangle, trapezoid, wherein a long side of the trapezoid points away from the sensor medium, and wherein a narrow side of the trapezoid points towards the sensor medium. This results, for example, in the technical advantage that particularly suitable shapes are provided for efficient flow enhancement. A segment of a circle or an ellipse can also be referred to as an arc. In one embodiment of the sensor unit, the shape of the flow concentrator is such that, for any direction in space, there is a surface element on an outside of the flow concentrator whose normal direction coincides with that direction. This results, for example, in the technical advantage that a particularly suitable shape is provided for efficient flow enhancement. According to the foregoing embodiment, it is provided that for every arbitrary direction in space (360° in 3D, called 4π in mathematics), there is a surface element on the outside of the flow concentrator whose normal direction coincides with that direction. For example: upward direction ((0 0 1) direction): the flow concentrator has a surface element on its outside whose surface normal also runs in the (0 0 1) direction. In one embodiment of the sensor unit, the magnetometer comprises several, in particular three, separately formed and arranged sensor media, wherein the flux concentrator is configured to concentrate the external magnetic field at at least one location in at least one of the several sensor media, regardless of any rotation of the several sensor media about several, in particular three, different axes of rotation defined by the shape of the flux concentrator. This results, for example, in the technical advantage that there is at least one sensor medium in which an increase in flow occurs. In one embodiment of the sensor unit, it is provided that the shape of the flux concentrator defines one or more positions at which, depending on the orientation of the external magnetic field relative to the flux concentrator, a flux increase occurs, wherein the at least one sensor medium is arranged at one of the one or more positions. This results, for example, in the technical advantage that there is an increase in flux within the sensor medium, so that the magnetic field can be measured efficiently. In one embodiment of the sensor unit, it is provided that one or more positions are located on an end face of the flow concentrator and / or along a closed curve, in particular a circle or ellipse. This results, for example, in the technical advantage that particularly suitable positions are provided. In one embodiment of the sensor unit, the magnetometer is provided to be an element selected from the following group of magnetometers: NV magnetometer, fluxgate magnetometer, TMR magnetometer. This results, for example, in the technical advantage that particularly suitable magnetometers are provided. "TMR" stands for "tunnel magnetoresistance". In one embodiment of the sensor unit, the magnetometer is an NV magnetometer, and the sensor medium comprises a diamond crystal, and the external magnetic field concentrated by the flux concentrator defines a bias magnetic field to eliminate the degeneracy of the energy levels of the different electron spin states. This results, for example, in the technical advantage that the degeneracy of the energy levels can be efficiently removed, so that the magnetic field can be measured efficiently. “NV” stands for “nitrogen vacancy”. Since the NV center in the diamond crystal has four possible arrangements, which become visible as separate frequency splittings in the fluorescence spectrum due to the degeneracy of the energy levels of the different electron spin states caused by the bias magnetic field, the magnetic field direction and strength can be extracted for each of the four crystal directions, so that the source of the magnetic field to be measured can also be localized. NV magnetometers based on nitrogen vacancies in diamond (NV centers) can be operated with a magnetic offset field to cancel the degeneracy of the energy levels of the different electron spin states, in other words, to split the resonances, for example, in the ODMR spectrum (optically detected magnetic resonance). This magnetic offset field is the bias magnetic field. The magnetic flux density required for this is referred to as B0. It can be generated, for example, with permanent magnets and / or with electromagnets or coils. Due to its small magnitude, the unconcentrated Earth's magnetic field is insufficient for this purpose. According to the concept described here, the Earth's magnetic field can also be efficiently concentrated by the flux concentrator at the location of the sensor medium, for example the diamond crystal, so that a sufficiently large bias magnetic field is generated at the location of the sensor medium, causing a degeneracy of the energy levels, which advantageously makes it possible to locate the source of the magnetic field to be measured. Thus, coils and / or electromagnets and / or permanent magnets for generating the bias magnetic field can be advantageously omitted. Therefore, a sensor unit according to one embodiment can be free of coils and / or electromagnets and / or permanent magnets for generating the bias magnetic field. This means that, for example, the use of previously required permanent magnets, coils, etc., can either be completely eliminated or they can be designed differently. For example, coils with fewer turns and thus lower energy losses and / or permanent magnets with lower magnetization can be used, since a significant portion of the bias magnetic field generation results from the Earth's magnetic field concentrated at the location of the sensor medium by the flux concentrator. Here, a coil or electromagnet used to generate the bias magnetic field may, for example, have the disadvantage that the intrinsic noise of a current driver belonging to the coil or electromagnet can have a linear effect on the noise of B0. Here, the use of one or more permanent magnets can have the disadvantage that temperature fluctuations and / or mechanical expansions can lead to drifts or noise in B0. These two disadvantages mentioned above can therefore be efficiently avoided, enabling a correspondingly lower-noise magnetic field measurement. Depending on the chosen form of the flux concentrator, it can be efficiently achieved that in every orientation of the sensor unit and thus of the diamond crystal, generally sensor medium, with respect to the Earth's magnetic field, the Earth's magnetic field is concentrated at least at one point or location in the diamond crystal or in the diamond volume, generally sensor medium volume. In general, a basic form of a flow concentrator as described can have multiple turns and / or discontinuous and / or piecewise constant rotation angles. In particular, a flow concentrator as described has an outer concentrator surface that is larger than an inner concentrator surface on which, for example, the sensor medium, especially the diamond crystal(s), is arranged. A sensor medium as described above comprises, for example, one or more separately formed diamond crystals. A flow concentrator, as described above, runs, for example, along a [path / circle] and / or is, for example, at least partially wrapped around a partial circle, in particular a semicircle or three-quarter circle, or a full circle. A partial circle can therefore be, in particular, a semicircle or a three-quarter circle. The phrase “at least one” means “one or more”. The embodiments and examples described here can be combined in any way, even if this is not explicitly described. The invention is explained in more detail below with reference to preferred embodiments. Figure 1 shows a sensor unit for measuring magnetic fields, Figure 2 a first flux concentrator, Figure 3 a flux increaser, Figure 4 a close-up of the flux increaser shown in Figure 3, Figure 5 a second flux concentrator, Figure 6 a third flux concentrator, and Figure 7 a flux increaser. The same reference symbols can be used for identical features in the following. Fig. 1 shows symbolically a sensor unit 101 for measuring magnetic fields, comprising: a magnetometer 105 comprising at least one sensor medium 103 and a flux concentrator 107, which is arranged to concentrate an external magnetic field, in particular Earth's magnetic field, at at least one location in the at least one sensor medium 103, independently of a rotation of the at least one sensor medium 103 about at least one axis of rotation 109 defined by a shape of the flux concentrator 107. For example, the shape of the flux concentrator 107 defines two, in particular 3, different axes of rotation, the shape being such that, regardless of any rotation about the two, in particular the three, axes of rotation, the external magnetic field, in particular the Earth's magnetic field, is concentrated at at least one location, in particular at several locations, in which at least one sensor medium 103, in particular in several sensor media, is concentrated. An axis of rotation, as described above, can be, for example, an axis of a three-dimensional coordinate system, in particular a three-dimensional Cartesian coordinate system. With three axes, a sensor unit can thus be provided in which, regardless of the sensor unit's position in three-dimensional space, there is always at least one location in at least one sensor medium where an external magnetic field is concentrated. The magnetic field to be measured and the external magnetic field can, for example, be different magnetic fields. The external magnetic field can, for example, define or be a bias magnetic field. Fig. 2 shows a first flux concentrator 201, as it can be used in a sensor unit for measuring magnetic fields. The first flux concentrator 201 has the shape of a disk segment, the tip of which 203 is truncated. This means that the disk segment is blunt. A diamond crystal 205 is arranged at the blunt tip 203 as a sensor medium. Those magnetic fluxes of an external magnetic field whose field lines follow a normal direction 207 of the circular arc 209 of the disk segment are concentrated in the diamond crystal 205. For orientation, a three-dimensional Cartesian coordinate system 211 is shown in Fig. 2. Reference symbol 213 denotes the x-axis. Reference symbol 215 denotes the y-axis. Reference symbol 217 denotes the z-axis. Fig. 3 shows graphically the increase in flow caused by the first flow concentrator 201 of Fig. 2 as described above. A distance in arbitrary units is plotted on an x-axis 303. A distance in arbitrary units is plotted on a y-axis 305. A field line of an external magnetic field is symbolically represented by an arrow with the reference symbol 307. This field line 307 runs along a normal direction 207 of the circular arc 209. Figure 3 further shows a scale 307, which represents a flux density in arbitrary units through different hatching patterns. The flux density on the scale 307 increases from bottom to top. Fig. 4 shows a close-up of the blunt tip 203 shown in Fig. 3. Figures 3 and 4 clearly show the increase in flow at the location of the blunted tip 203, resulting in an increase in flow in the sensor medium, which is not shown in Figures 3 and 4 for the sake of clarity. Fig. 5 shows a second flux concentrator 501, as it can be used in a sensor unit for measuring magnetic fields. In this process, the two-dimensional flow concentrator 201 of Fig. 2 was transferred into three dimensions, so that the second flow concentrator 501 has a helical shape. The three-dimensional flux concentrator 501 can concentrate magnetic fluxes with field lines in the xy-plane 503 along a rotational axis 505. The flux is also increased for fluxes along the rotational axis 505. The concentration takes place along the rotational axis 505, so that a sensor medium arranged along, on, or at the rotational axis 505 experiences a corresponding increase in flux. Fig. 6 shows a third flux concentrator 601, as it can be used in a sensor unit for measuring magnetic fields. The third flux concentrator 601 has a helical shape wound spirally around a semi-elliptical arc, or for example, a semicircle, 603. Such a shape causes field lines in the x-direction, y-direction, and z-direction to be concentrated at several locations on the arc 603, for example, the semicircle. This means that, during any rotation of the third flux concentrator 601 in an external magnetic field, for example, the Earth's magnetic field, a normal to an outer surface element of the helical shape of the third flux concentrator 601 always points in the direction of the external magnetic field. Such an outer surface element is indicated by the reference symbol 605. The arc 603 is thus a segment of an ellipse. For example, several diamond crystals are arranged along arc 603, in particular semicircle, so that a corresponding increase in flux can be effected in these depending on a current position or pose of the sensor unit. The third flow concentrator 601 has two end faces 607, 609, at which a corresponding increase in flow can also be effected. For example, one or more diamond crystals, or more generally, sensor medium, are arranged on one or both end faces 607, 609. Fig. 7 shows graphically the increase in flow caused by the third flow concentrator 601 of Fig. 6 as described above. Reference numerals 701, 703, 705 and 707 designate areas along arc 603, in particular semicircle, within which an increase in flux occurs in the presence of an external magnetic field, depending on the specific direction of incidence of the field lines, whereby there is always at least one area within which an increase in flux occurs regardless of the current position of the sensor unit. An arrangement of one or more diamond crystals within three of these areas 701, 703, 705, 707 is therefore sufficient to cause a flux enhancement in at least one of the areas and thus also in at least one or more corresponding diamond crystals for any direction of incidence of a magnetic field. The areas 701, 707 correspond to the end faces 607, 609 of the third flow concentrator 601 shown in Fig. 6. In general, a basic form of a flow concentrator as described can have multiple turns and / or discontinuous and / or piecewise constant rotation angles. In particular, a flow concentrator as described has an outer concentrator surface that is larger than an inner concentrator surface on which, for example, the sensor medium, especially the diamond crystal(s), is arranged. A sensor medium as described above comprises, for example, one or more separately formed diamond crystals. A flow concentrator, as described above, runs along a path and / or is, for example, at least partially wrapped around a partial circle, in particular a semicircle or three-quarter circle, or a full circle. A partial circle can therefore be, in particular, a semicircle or a three-quarter circle. When the term "circle" is used in this description, the term "ellipse" should always be implied, and vice versa. QUOTES INCLUDED IN THE DESCRIPTION This list of documents cited by the applicant was automatically generated and is included solely for the reader's convenience. The list is not part of the German patent or utility model application. The DPMA accepts no liability for any errors or omissions. Cited patent literature DE 10 2018 220 234 A1

[0003] DE 10 2018 214 617 A1

[0003] US 10,705,163 B2

[0004] DE 10 2020 119 414 A1

[0005]

Claims

Sensor unit (101) for measuring magnetic fields, comprising: a magnetometer (105) comprising at least one sensor medium (103) and a flux concentrator (107) which is configured to concentrate an external magnetic field, in particular Earth's magnetic field, at at least one location in the sensor medium (103), independently of a rotation of the at least one sensor medium (103) about at least one axis of rotation (109) defined by a shape of the flux concentrator (107). Sensor unit (101) according to claim 1, wherein the shape of the flow concentrator (107) comprises at least one element selected from the following group of shapes: disc segment, truncated disc segment (201), at least a part, in particular half, of a spiral torus, a helix shape (601) wound around at least a portion of a circle, in particular a full circle, three-quarter circle or semicircle, or an ellipse, in particular a half-ellipse, three-quarter ellipse or full ellipse, triangle, trapezoid, wherein a long side of the trapezoid points away from the sensor medium, and wherein a narrow side of the trapezoid points towards the sensor medium. Sensor unit (101) according to claim 1 or 2, wherein the shape of the flow concentrator (107) is such that there is a surface element on an outside of the flow concentrator (107) for any direction in space, the normal direction of which coincides with that direction. Sensor unit (101) according to one of the preceding claims, wherein the magnetometer (105) comprises several, in particular three, separately formed and arranged sensor media, wherein the flux concentrator (107) is configured to concentrate the external magnetic field at at least one location in at least one of the several sensor media, irrespective of any rotation of the several sensor media about several, in particular three, different axes of rotation defined by the shape of the flux concentrator (107). Sensor unit (101) according to one of the preceding claims, wherein the shape of the flux concentrator (107) defines one or more positions (701, 703, 705, 707) at which, depending on an orientation of the external magnetic field relative to the flux concentrator, a flux increase occurs, wherein the at least one sensor medium is arranged at one of the one or more positions (701, 703, 705, 707). Sensor unit (101) according to claim 5, wherein the one or more positions (701, 703, 705, 707) are each located on an end face (607, 609) of the flow concentrator and / or along a closed curve, in particular a circle or ellipse. Sensor unit (101) according to one of the preceding claims, wherein the magnetometer (105) is an element selected from the following group of magnetometers: NV magnetometer, fluxgate magnetometer, TMR magnetometer. Sensor unit (101) according to claim 7, wherein the magnetometer (105) is an NV magnetometer, and wherein the sensor medium comprises a diamond crystal, and wherein the external magnetic field concentrated by the flux concentrator (107) defines a bias magnetic field to remove the degeneracy of the energy levels of the different electron spin states.

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