Method for manufacturing a sensor head

Abstract

Method for manufacturing a sensor head (SK) comprising the following steps: Provision (140) of an optical fiber (OF), - wherein the optical fiber (OF) has a first end (OF1) and a second end (OF2); Providing (145) a liquid and curing wavelength (λ) by means of electromagnetic radiation H ) curable carrier material (TM), - wherein the carrier material (TM) contains a multitude of diamonds (DM) and - wherein one or more or all of these diamonds (DM) have NV centers (NVZ) and / or other paramagnetic centers and - wherein the NV centers (NVZ) of the diamonds (DM) of the support material (TM) and / or the other paramagnetic centers of the diamonds (DM) of the support material (TM) emit at least one fluorescence radiation (FL) when irradiated with pump radiation (LB); Wetting (150) the first end (ELWL1) of the optical fiber (TM) to a wetting length (L B ) with the carrier material (TM); Feeding (155) electromagnetic radiation into the second end (ELWL2) of the optical fiber (LWL), - where the wavelength of this electromagnetic radiation is the curing wavelength (λ) H ) corresponds, - so that the carrier material (TM) at the first end (ELWL1) of the optical fiber (OF) hardens and - so that the carrier material (TM) at the first end (ELWL1) of the optical fiber (OF) transforms into a solid and - wherein the hardened carrier material (TM) then forms the sensor element (NV) and - wherein the sensor element (NV) then comprises diamonds (DM) with NV centers (NVZ) of the diamonds (DM) and / or with other paramagnetic centers of the diamonds (DM) which, when irradiated with pump radiation (LB), emit at least one fluorescence radiation (FL); Removal (160) of the uncured carrier material (TM), in particular by means of a solvent, wherein the remaining film of the carrier material (TM) at the first end (ELWL1) of the optical fiber (LWL) forms the sensor element (NV); Providing (165) a sensor head housing (GH) of the sensor head (SK) with a channel (KN) and an excitation source for magnetic excitation (H), in particular a permanent magnet (PM); Installation (170) of the optical fiber (OF) with the newly formed sensor element (OF) into the channel (OF) of the sensor head housing (SH) of the sensor head (SH) and installation of the excitation source for a magnetic excitation (H) into the sensor head housing (SH) of the sensor head (SH); Use (180) of the sensor head (SK) for spatially resolved measurement of the magnetic properties of the material of a workpiece near the surface (OF) of the workpiece, where the distance between the center point (MP) of the end face (EF) of the first end (ELWL1) of the optical fiber (OF) and the surface (OF) of the workpiece - smaller than five times the diameter (D LWLMH ) of the sheathed optical fiber (OF) and / or - smaller than twice the diameter (D LWLMH ) of the sheathed optical fiber (OF) and / or - smaller than the diameter (D LWLMH ) of the sheathed optical fiber (OF) and / or - smaller than half the diameter (D LWLMH ) of the sheathed optical fiber (OF).

Description

Field of invention

[0001] The invention relates to a sensor head for high spatial resolution measurement of magnetic material properties on the surface of a workpiece, wherein the sensor head has a sensor element with a plurality of diamonds of different orientation to each other and to the sensor head housing, and wherein diamonds of these diamonds comprise NV centers or other paramagnetic centers. General Introduction

[0002] A recurring problem is the detection of cracks and other defects in the surfaces of ferromagnetic workpieces. While corresponding measurement methods exist in the prior art, they exhibit insufficient spatial resolution to detect small cracks.

[0003] This document provides only brief bullet points on the principles of non-destructive material testing with regard to the state of the art.

[0004] When measuring workpieces using magnetic field measurement, the use of Hall sensors / coils to measure magnetic stray fields / eddy current fields presents the following problems: these measurement methods require a large measurement volume at a limited distance to the workpiece and a large measurement cross-section. The corresponding devices are not diamagnetic and therefore alter the object being measured, i.e., the magnetic field.

[0005] The method and device presented here are intended to remedy this. State of the art

[0006] Wireless devices for detecting magnetic fields are already known from DE 10 2019 120 076 A1, DE 11 2020 003 569 A5, DE 11 2020004650 A5, DE 10 2021 101 565 A1 and EP 3 874 343 A2.

[0007] Methods for the production of NV centers are known from DE 10 2020 109 477 A1.

[0008] The commutation of an electric motor by means of a wireless magnetic field measurement is known from the still unpublished German patent application DE 10 2022 121 444.3.

[0009] The production of a suitable optical waveguide is known from the still unpublished German patent application DE 10 2022 122 505.7.

[0010] A sensor comprising a magnet is known from WO 2022 / 096 891 A1. According to the technical teaching of WO 2022 / 096 891 A1, the magnet is arranged such that it applies an inhomogeneous magnetic field to a specific volume. The sensor of WO 2022 / 096 891 A1 further comprises a magnetometer with an active element for detecting the magnetic field in a volume that contains the specified volume.

[0011] A detection system for orthogonal cracks based on NV color center detection technology is known from patent CN 114 994 006 A. The detection system of CN 114 994 006 A comprises an excitation end, a collecting end, and a magnetization detection front end. The technical teaching of CN 114 994 006 A uses the excitation end to generate excitation light, which acts on the front end of the magnetization sensor. The front end of the magnetization sensor comprises a magnetizing section and a detection section, the magnetizing section being used to magnetize a ferromagnetic object to be detected. The magnetizing section of the device of CN 114 994 006 A includes a magnetization interval. If a crack on the ferromagnetic object to be detected is positioned within the magnetization interval, the device CN 1 14 994 006 A can generate a magnetic stray field at the crack.The detection section of the device CN 1 14 994 006 A generates voltage fluorescence under the influence of excitation light and a magnetic stray field. The detection section of the device CN 114 994 006 A is used to receive, analyze, and process the voltage fluorescence. The magnetization section of the device CN 114 994 006 A comprises two groups of electromagnets. The magnetization directions of the two groups of electromagnets in the device CN 1 14 994 006 A are orthogonal to each other. The sensor section of the device CN 1 14 994 006 A comprises an optical sensor fiber. One end of the optical sensor fiber is a detection end, and diamond-shaped NV dye particles, attached to the fiber core, are arranged at the end face of the detection end.

[0012] A method for fabricating a fiber-optic quantum probe with controllable diamond particle doping is known from publication CN 1 12 146 782 A. The method of CN 112 146 782 A comprises the following steps: Step 1) Mixing the solution with an aqueous nano-diamond particle solution containing NV color centers; Step 2) Dissolving the prepared solution, doped with nano-diamond particles containing the NV color centers, using ultrasound via a sol-gel process, sealing and allowing the solution to stand, and completely hydrolyzing the solution to form a sol-gel; and 3) uniformly applying the sol-gel prepared in step 2) to the end face of the optical fiber, holding the optical fiber with a stepper motor, contacting the end face of the optical fiber with the sol-gel, pulling the end face of the optical fiber at a specific speed after a certain period of time to form a hemispherical gel film of a specific thickness and curvature, and curing to obtain the manufactured optical fiber quantum probe. According to the technical teaching of CN 112 146 782 A, the doping concentration of the nano-diamond particles containing NV color centers can be controlled.According to the technical document CN 112 146 782 A, the nanodiamond particles are uniformly mixed. Document CN 1 12 146 782 A states that the probe's manufacturing process is simple, its repeatability is high, and mass production is feasible.

[0013] A device for detecting stray flux in a pipeline is known from patent CN 1 14 720 553 A. The device described in CN 1 14 720 553 A is based on an optical fiber coupled to a diamond nitrogen vacancy color center.

[0014] The growth of silicon optical fibers using high-pressure chemical vapor deposition (HPVD) is described in the paper by Alex T. Hendrickson et al., "Diamond encapsulated silicon optical fibers synthesized by chemical vapor deposition." This paper addresses the challenge that semiconductor optical fibers coated with a protective diamond layer could theoretically achieve enormous power consumption and infrared functionality. In Hendrickson's paper, silicon optical fibers are grown using HPVD before being coated with 50 µm–300 µm diamond using microwave plasma-assisted HPVD. According to Hendrickson's paper, this coating conformally extends around the fiber cross-section, with the diamond crystallites in the layer being on the order of several micrometers.Scanning electron microscopy and Raman measurements, according to Alex T. Hendrickson's paper, show a complete coating of high-quality diamond around the fiber. The encapsulated silicon fibers are durable enough to withstand the diamond deposition process, as demonstrated by their ability to conduct infrared light, according to Hendrickson's paper. Task

[0015] The proposal is therefore based on the task of creating a solution that does not have the above disadvantages of the state of the art and offers further advantages.

[0016] This task is solved by the first claim and the concurrent claims. Solution to the task

[0017] In a sensor head of the proposed type, the task is solved as proposed by the fact that • that the sensor head uses NV-rich diamond dust as a magnetic field sensor and • that permanent magnets or coils (AC or DC magnetic fields) of the sensor head generate a magnetic test field that penetrates the surface of the workpiece, and • that the diamond material of the diamond stub forms the sensor element at a first fiber end of an optical waveguide and • that the sensor head enables a purely optical measurement of the magnetic field and thus the magnetic properties of the surface of the workpiece via the optical waveguide.

[0018] The document presented here proposes a device for detecting the magnetic flux density B in the vicinity of a disturbance on a ferromagnetic surface.

[0019] The sensor head SK comprises a sensor element NV with a carrier material TM. Preferably, a plurality of diamonds DM are embedded in the carrier material TM. The carrier material TM preferably comprises glass and / or a cured plastic. The carrier material TM fixes the diamonds DM and prevents their repositioning. Preferably, the carrier material TM is cured after solidification during the manufacturing process for the pump wavelength λ. pmpThe pump radiation LB and the fluorescence radiation FL of the NV centers in the diamonds DM are transparent. One, several, or all of these diamonds DM typically exhibit NV centers NVZ. The magnetic flux density B acts on the NV centers NVZ of the sensor element NV. Typically, the magnetic flux density B reduces the intensity of the fluorescence radiation FL. For the ingress of pump radiation LB from a pump radiation source PL to the sensor element NV, the sensor head SK preferably has an optical fiber LWL. The pump radiation LB preferably has a pump radiation wavelength λ. pmp exhibiting wavelengths in the range of 400 nm to 700 nm and / or preferably 450 nm to 650 nm and / or preferably 500 nm to 550 nm and / or preferably 515 nm to 540 nm. A wavelength of 532 nm as the pump radiation wavelength λ is clearly preferred. pmpIn the case of NV centers in diamond or in diamonds, a laser diode from Osram, type PLT5 520B, for example, can be used as a pump radiation source PL1 with a pump radiation wavelength λ of 520 nm. pmp suitable. The NV centers NVZ of the sensor element NV typically emit, when irradiated with pump radiation LB of the pump radiation wavelength λ described above. pmp a fluorescence radiation FL with a typical fluorescence wavelength λ flof approximately 637 nm at NV centers. Other wavelengths can be achieved by plasmonic coupling with metallic nanocrystals in the support material TM. The optical properties of the NV centers can be modified by combining the nanodiamonds or diamonds DM in the support material TM with metallic nanoparticles. The optical waveguide LWL preferably transports the fluorescence radiation FL of the sensor element NV to a photodetector PD. The proposed device further comprises a sub-device, in particular a dichroic mirror F1, to separate the fluorescence radiation FL from the pump radiation LB, so that essentially only fluorescence radiation FL and as little pump radiation LB as possible is incident on the photodetector PD. This sub-device, in the form of a filter F1 or dichroic mirror, allows the passage of radiation with the fluorescence wavelength λ. flthe fluorescence radiation FL - e.g. 637 nm in NV centers NVZ with a phonon sideband from 637 nm to 850 nm - passes in the direction of the photodetector PD, while the radiation with the pump radiation wavelength λ pmp The device prevents the pump radiation LB from the pump radiation source PL from passing through, or guides the modulated pump radiation LB so that it does not reach or influence the photodetector PD. The photodetector PD converts the intensity signal of the fluorescence radiation FL into a receiver output signal S0. The device evaluates the receiver output signal S0 to obtain information about the distortion of the magnetic field B of a permanent magnet PM by cracks RI and / or depressions in the surface of a ferromagnetic material FM.

[0020] The proposed device has the advantage that the magnetic field of cracks RI and / or depressions in the surface of a ferromagnetic material FM is not disturbed by connecting leads, such as those used in magnetic field measurements with Hall sensors. Furthermore, the sensor element NV is completely diamagnetic. Due to galvanic isolation, feedback of magnetic fields and / or interfering fields to the evaluation electronics of the sensor system via the sensor element NV and the optical fiber LWL is highly unlikely. This allows the system to be used even in high-voltage systems with device components driven by very high voltages. Prior art systems do not exhibit this capability.

[0021] In one variant, the diamonds DM in the carrier material TM are oriented in substantially different ways relative to each other. This has the manufacturing advantage that alignment of the diamonds DM is no longer necessary, and the manufacturing process for producing the sensor element NV can, for example, use diamond powder containing a very large number of very small diamonds DM. A sensor element NV with such a disordered multitude of diamonds DM has the advantage that the measurement of the magnetic flux density B is isotropic. This means that the sensor element NV only detects the magnitude of the magnetic flux density B, but not its direction. This has the advantage that alignment of the sensor element NV, the optical fiber LWL, and the sensor head SK is no longer necessary.The assembly of such a sensor element NV can be carried out by auxiliary personnel or less precise machine devices, which simply need to insert the sensor element NV with the optical fiber LWL into the channel KN of the sensor head SK. This drastically reduces the manufacturing costs for such a sensor head SK. To achieve spatial isotropy, it is therefore advantageous if the orientation of the diamonds DM is stochastically essentially uniformly distributed.

[0022] In the course of developing the technical teaching of this document, the applicant recognized that, as explained above, it is also advantageous if the sensor element NV is located in the stray field BSTR of the magnetic field of the permanent magnet PM. Other field excitations are conceivable instead of a permanent magnet. These are covered by the description "permanent magnet PM" within the meaning of this document.

[0023] To minimize the number of optical fibers (OFs) and keep modifications to the sensor head (SK) to a minimum, it is advantageous to use a single OF for supplying the pump radiation (LB) from the pump radiation source (PL) to the sensor element (NV) and for returning the fluorescence radiation (FL) from the sensor element (NV) to the photodetector (PD). In this case, only a single channel (KN) is required for mounting the OF, so the first channel (KN) is identical to the second channel (KN). In the following text, such a channel (KN) is referred to as the common channel (KN).

[0024] Thus, the proposed sensor head SK preferably comprises a sensor element NV with a plurality of diamonds DM with NV centers NVZ in a carrier material TM and a first optical fiber LWL to which the sensor element NV is attached, wherein the optical fiber LWL transports the pump radiation LB of the pump radiation source PL to the sensor element NV, so that the pump radiation LB irradiates the sensor element NV and the NV centers NVZ emit fluorescence radiation FL, which the optical fiber LWL detects and transports back towards the photodetector PD.

[0025] The optical fiber LWL can be inserted parallel to the contact surface AF of the sensor head SK, in which case the sensor element NV is preferably located in the stray field of the cracks RI and / or depressions in the surface of a ferromagnetic material FM. Alternatively, the optical fiber LWL can be inserted perpendicular to the contact surface AF of the sensor head SK via a vertical channel and advanced to the vicinity of the contact surface AF, so that the sensor element NV then detects the magnetic flux density B in the stray field of the cracks RI and / or depressions in the surface of the ferromagnetic material FM. The sensor element NV can also be advanced to the immediate vicinity of the contact surface AF of the sensor head SK, but this increases the probability of damage to the sensor head SK during measurement operation due to movement along the contact surface AF of the sensor head SK.

[0026] If the return of the fluorescence radiation FL from the sensor element NV to the photodetector PD is to be carried out separately from the supply of the pump radiation LB to the sensor element NV, in this case the sensor head SK preferably comprises a second optical waveguide LWL, which detects fluorescence radiation FL from the sensor element NV and transports the fluorescence radiation FL in the direction of the photodetector PD.

[0027] As explained above, the first optical fiber (OP) and the second OP are preferably identical. This document refers to such an OP as a common optical fiber. Such a common OP saves on calibration effort, reduces assembly complexity, and saves material, thus offering advantages. In particular, it reduces the necessary modifications to the sensor head itself.

[0028] The first optical fiber (OP) has a first end and a second end. The second optical fiber (OP) also has a first end and a second end. The common optical fiber (OP) likewise has a first end and a second end. This document proposes attaching the sensor element (NV) to the first end of the first optical fiber (OP) and / or the second optical fiber (OP), or the common optical fiber (OP), in order to stabilize the optical coupling between the optical fiber (OP) and the sensor element (NV).

[0029] If the first end of the first and / or second or common optical waveguide LWL is enveloped by the carrier material TM of the sensor element NV, this results in particularly good stabilization of this optical coupling.

[0030] Preferably, an end surface EF of the first end of the first and / or second or common optical fiber LWL forms a flat end surface EF perpendicular to the center line ML of the optical fiber LWL. The center line ML typically corresponds to the optical axis of the optical fiber LWL. Such a flat end surface EF enables improved coupling of the electromagnetic pump radiation LB out of the optical fiber LWL and improved optical coupling of the fluorescence radiation FL into the optical fiber LWL. Preferably, the distance of one or more diamonds DM from this flat end surface EF is smaller than the pump radiation wavelength λ. pmp and / or preferably smaller than ½ the pump radiation wavelength λ pmp , and / or preferably smaller than 1 / 4 of the pump radiation wavelength λ pmp , and / or preferably smaller than 1 / 8 of the pump radiation wavelength λ pmp, and / or preferably smaller than 1 / 10 of the pump radiation wavelength λ pmp , and / or preferably smaller than 1 / 20 of the pump radiation wavelength λ pmp , and / or preferably smaller than 1 / 50 of the pump radiation wavelength λ pmp , and / or preferably smaller than 1 / 100 of the pump radiation wavelength λ pmp , , and / or preferably smaller than 1 / 200 of the pump radiation wavelength λ pmp , and / or preferably smaller than 1 / 500 of the pump radiation wavelength λ pmp , and / or preferably smaller than 1 / 1000 of the pump radiation wavelength λ pmp .

[0031] The center line ML, which is an imaginary auxiliary construction used to clarify the situation, intersects the end surface EF at a midpoint MP of the end surface EF. The thickness dl of the carrier material TM is preferably greater at this midpoint MP than the thickness dr at other points on the end surface EF of the first end of the first and / or second or common optical fiber LWL. This has the advantage that light is reflected back through the interface between the carrier material TM and the air into the optical fiber LWL, thus increasing efficiency.

[0032] Preferably, the carrier material TM forms a lens LWLL at the first end ELWL1 of the optical fiber LWL. The diameter DLWLL of the lens LWLL is typically smaller than the diameter DLWL of the optical fiber LWL. However, the diameter DLWLL of the lens LWLL can also be as large as the diameter DLWL of the optical fiber LWL, which, according to the experience gained during the development of the technical teaching of this document, is not optimal.

[0033] Preferably, the first optical fiber (OF) in the area of ​​the sensor head (SK) and / or within the sensor head (SK) is wholly or partially enclosed by a mechanical enclosure (MH). Preferably, the second optical fiber (OF) in the area of ​​the sensor head (SK) and / or within the sensor head (SK) is also wholly or partially enclosed by a mechanical enclosure (MH). Preferably, the common optical fiber (OF) in the area of ​​the sensor head (SK) and / or within the sensor head (SK) is also wholly or partially enclosed by a mechanical enclosure (MH) in the same manner. The mechanical enclosure (MH) supports and protects the respective optical fiber (OF) against the harsh conditions inside and outside the sensor head (SK). The mechanical enclosure (MH) inside the sensor head (SK) must generally meet special requirements regarding thermal and chemical stability against heat and operating fluids.The mechanical casing MH is therefore preferably made of glass or ceramic or the like. Most preferably, the mechanical casing comprises a mechanically flexible material, for example a fabric, such as a glass fabric.

[0034] The mechanical housing MH therefore preferably comprises a ceramic material or another non-magnetizable and / or electrically non-conductive material and / or a material stable at temperatures above 100°C and / or a material stable at temperatures above 140°C and / or a material stable at temperatures above 170°C and / or a material stable at temperatures above 200°C and / or a material stable at temperatures above 250°C, or includes or consists of these materials in extreme cases. This allows the sensor head to be used even at high temperatures of the ferromagnetic material FM.The mechanical casing MH can therefore be made of a ceramic material or of another non-magnetizable and / or electrically non-conductive material and / or of a material stable at temperatures above 100°C and / or of a material stable at temperatures above 140°C and / or of a material stable at temperatures above 170°C and / or of a material stable at temperatures above 200°C and / or of a material stable at temperatures above 250°C.

[0035] Preferably, the mechanical casing MH is at least partially a tube, a capillary, or a cannula into which the respective optical fiber LWL can be inserted. This simplifies the manufacturing of the system consisting of the optical fiber LWL, the sensor element NV, and the mechanical casing MH. The inner diameter Dro of such a tube, capillary, or cannula is preferably only slightly larger than the diameter of the optical fiber lens LWLL and the diameter DLWL of the optical fiber LWL.

[0036] To minimize the ingress of ambient light to the sensor element NV during operation, it is advantageous to completely or partially seal the first gap between the edge of the channel KN and the first optical fiber LWL with an optically opaque filler FM. For the same reason, it is advantageous to completely or partially seal the second gap between the edge of the second channel KN and the second optical fiber LWL with an optically opaque filler FM, and / or to completely or partially seal the common gap between the edge of the channel KN and the common optical fiber LWL with an optically essentially opaque filler FM. The common filler FM can secure the respective optical fiber to the housing of the sensor head SK.

[0037] Preferably, the device is configured to determine the temporal value profile of the intensity of the fluorescence radiation FL, particularly in the form of a receiver output signal S0.

[0038] Furthermore, the device is preferably configured to determine the temporal profile of the amplitude value of the intensity of the fluorescence radiation FL from the intensity of the fluorescence radiation FL, in particular from the receiver output signal S0 and especially by means of a lock-in amplifier LIV or a functionally equivalent sub-device. Finally, the device is preferably configured to display or otherwise signal a value depending on the determined temporal profile of the amplitude value of the intensity of the fluorescence radiation FL.

[0039] Preferably, the proposed device is configured, in particular by means of a high-pass filter or a functionally equivalent filter, to determine an alternating component and / or direct component of the temporal course of the amplitude value of the temporal value course of the intensity of the fluorescence radiation FL from the temporal course of the amplitude value of the temporal value course of the intensity of the fluorescence radiation FL.

[0040] Preferably, the device is configured, in particular by means of a second low-pass filter TP2, to determine a low-frequency DC component in the temporal profile of the amplitude value of the intensity of the fluorescence radiation FL. The device can use this DC component to monitor the sensor element NV and the optical path and to detect deviations from expected values. For this purpose, the device compares the value of the DC component with an expected value interval. If the value of the DC component lies outside the expected value interval, the device preferably concludes that a fault has occurred and triggers appropriate measures. One such measure could be, for example, that the half-bridge controller CTR transmits a signal via an external data bus EXTDB to a higher-level computer system, which then initiates all further actions.

[0041] Preferably, the device is configured to separate this low-frequency DC component in the temporal course of the amplitude value of the temporal value profile of the intensity of the fluorescence radiation FL from the temporal course of the amplitude value of the temporal value profile of the intensity of the fluorescence radiation FL and thus to determine the AC component of the temporal course of the amplitude value of the temporal value profile of the intensity of the fluorescence radiation FL.

[0042] An exemplary application of the proposed optical fiber LWL is the measurement of the magnetic field of a ferromagnetic material FM. However, the uses of the proposed optical fiber LWL and the sensor head SK are not limited to this. This document proposes an optical fiber LWL with the sensor element NV for such and other applications with similar measurement tasks. The sensor element NV comprises a substrate material TM in which a plurality of diamonds DM are embedded. One, more, or all of these diamonds DM exhibit one or more NV centers NVZ and / or one or more other paramagnetic centers. The NV centers NVZ of the sensor element NV and / or the other paramagnetic centers of the sensor element NV emit at least one fluorescence radiation FL when irradiated with pump radiation LB.The special feature of the optical fiber LWL proposed in the document presented here is that the carrier material TM is preferably a carrier material TM cured by means of electromagnetic radiation and that the carrier material TM, after curing, is suitable for radiation with a pump radiation wavelength λ. pmp The pump radiation LB, with which the NV centers NVZ and / or the other paramagnetic centers are pumped, is essentially transparent. Essentially means that the losses that undoubtedly occur are still so small that the functionality of the device in the application in question is still ensured. Similarly, the support material TM should be transparent to radiation with a fluorescence wavelength λ. flThe fluorescence radiation LB of the NV centers NVZ or paramagnetic centers should be essentially transparent. "Essentially" in this context means that the losses that undoubtedly occur are still so small that the functionality of the device in the application in question is still ensured. The production of such an optical fiber LWL is particularly simple and process-reliable with a high C by curing a previously liquid carrier medium TM. pk -value to manufacture.

[0043] This document proposes, as an application example, a device for detecting the magnetic flux density B in a channel KN of a sensor head SK and / or in the stray field BSTR of a permanent magnet PM of the sensor head SK. The sensor head SK preferably comprises a sensor element NV with a carrier material TM. A plurality of diamonds or nanodiamonds DM are preferably embedded in the carrier material TM. The carrier material TM preferably comprises glass and / or a cured plastic. The carrier material TM fixes the diamonds DM relative to the first end ELWL1 of the optical fiber LWL and prevents repositioning of the diamonds DM. Preferably, after solidification during the manufacturing process, the carrier material TM is suitable for radiation with the pump radiation wavelength λ. pmp the pump radiation LB and for radiation with the fluorescence wavelength λ flThe fluorescence radiation FL of the NV centers NVZ or paramagnetic centers in the diamonds DM or nanodiamonds is transparent. One, several, or all of these diamonds or nanodiamonds DM typically exhibit NV centers NVZ. The magnetic flux density B in the stray field BSTR of the permanent magnet PM acts on the NV centers NVZ or the paramagnetic centers in the sensor element NV of the sensor head SK. Typically, the magnetic flux density B reduces the intensity of the fluorescence radiation FL of the NV centers NVZ or paramagnetic centers in the sensor element NV. The sensor head housing GH preferably has a first channel KN for supplying pump radiation LB from the pump radiation source PL to the sensor element NV via an optical fiber LWL or a similar optical system.In the case of NV centers as paramagnetic centers, the pump radiation LB preferably has a pump radiation wavelength λ. pmp exhibiting wavelengths in the range of 400 nm to 700 nm and / or preferably 450 nm to 650 nm and / or preferably 500 nm to 550 nm and / or preferably 515 nm to 540 nm. A wavelength of 532 nm as the pump radiation wavelength λ is clearly preferred. pmp In the case of NV centers in diamond or in diamonds, a laser diode of type Osram PLT5 520B, for example, can be used as a pump radiation source PL with a pump radiation wavelength of 520 nm λ. pmp suitable. The NV centers NVZ of the sensor element NV typically emit, when irradiated with pump radiation LB of the pump radiation wavelength λ described above. pmp a fluorescence radiation FL with a typical fluorescence wavelength λ flof approximately 637 nm at NV centers NVZ. Other wavelengths can be achieved by plasmonic coupling with metallic nanocrystals in the support material TM. The optical properties of the NV centers NVZ or paramagnetic centers in the sensor element NV can be modified by combining the nanodiamonds or diamonds DM in the support material TM of the sensor element NV with metallic nanoparticles. The sensor head housing GH preferably has a second channel KN for the emission of fluorescence radiation FL from the sensor element NV to a photodetector PD. The proposed device further includes a sub-device, in particular a dichroic mirror F1, to separate the fluorescence radiation FL from the pump radiation LB, so that essentially only fluorescence radiation FL and as little pump radiation LB as possible is incident on the photodetector PD.This sub-device in the form of a filter F1 or dichroic mirror preferentially allows the passage of radiation with the fluorescence wavelength λ. fl the fluorescence radiation FL - e.g. 637 nm in NV centers NVZ with a phonon sideband from 637 nm to 850 nm - passes in the direction of the photodetector PD, while the radiation with the pump radiation wavelength λ pmpThe pump radiation LB from the pump radiation source PL is prevented from passing through, or the modulated pump radiation LB is guided in such a way that it does not reach or influence the photodetector PD. The photodetector PD converts the intensity signal of the fluorescence radiation FL into a receiver output signal S0. The device evaluates the receiver output signal S0 to obtain information about the values ​​of magnetic material parameters of the material at the surface OF of a workpiece, or information that includes this information. Preferably, the material of the workpiece near the surface OF comprises a ferromagnetic material FM.

[0044] The proposed device has the advantage that the magnetic field of the permanent magnet PM and the ferromagnetic material FM of the workpiece is not disturbed by connecting leads, as is the case, for example, with Hall-effect sensors in magnetic field measurements. Furthermore, the sensor element NV is completely diamagnetic. Due to the galvanic isolation, feedback from the workpiece's fields to the evaluation electronics of the sensor system via the sensor element NV, the sensor head SK, and the optical fiber LWL is highly unlikely. This allows the system to be used even in high-voltage systems with workpieces at very high electrical potentials. It is also conceivable that the workpiece could be very hot or very cold. A temperature range of 0°C to 80°C is possible.With appropriate design of the sensor head, the optical fiber (OF), the mechanical housing (MH), the substrate material (TM), and the sensor head housing material (GH), temperatures up to 700°C and down to absolute zero are conceivable for the workpiece and the ferromagnetic material (FM). Prior art systems do not demonstrate this.

[0045] Preferably, NV centers NVZ or the paramagnetic centers of the sensor element NV are not located in the stray field BSTR of the permanent magnet PM.

[0046] Preferably, the diamonds or nanodiamonds DM in the carrier material TM are oriented substantially differently from one another, each with a substantially different orientation. This has the manufacturing advantage that alignment of the diamonds or nanodiamonds DM is no longer necessary, and the manufacturing process for producing the sensor element can, for example, use diamond powder containing a very large number of very small diamonds or nanodiamonds DM. A sensor element NV with such a disordered multitude of diamonds or nanodiamonds DM has the advantage that the measurement of the magnetic flux density B is isotropic. This means that the sensor element NV only detects the magnitude of the magnetic flux density B, but not its direction. This has the advantage that alignment of the sensor element NV and the optical fiber LWL in the sensor head SK is no longer necessary.The assembly of such a sensor element NV can be carried out by auxiliary personnel or less precise machine devices, which simply need to insert the sensor element NV with the optical fiber LWL into a designated channel KN in the sensor head housing GH and secure it there, for example, by gluing or screwing. This drastically reduces the manufacturing costs for such a sensor head SK. To achieve spatial isotropy, it is therefore advantageous if the orientation of the diamonds or nanodiamonds DM is stochastically and essentially uniformly distributed within the sensor element NV.

[0047] In the course of developing the technical teaching of this document, the applicant has recognized that, in accordance with the preceding explanations, it is also advantageous if the sensor element NV is located in the stray field BSTR of the permanent magnet PM.

[0048] To minimize the number of optical fibers (OF) and keep modifications to the sensor head (SK) to a minimum, it is advantageous to use a single OF for supplying the pump radiation (LB) from the pump radiation source (PL) to the sensor element (NV) and for returning the fluorescence radiation (FL) from the sensor element (NV) to the photodetector (PD). In this case, only a single channel (KN) is required for mounting the OF in the sensor head housing (GH), so that the first channel (KN) is identical to the second channel (KN). In the following text, such a channel (KN) is referred to as the common channel (KN).

[0049] Thus, the proposed sensor head SK comprises a sensor element NV with a plurality of diamonds or nanodiamonds DM with NV centers NVZ and / or other paramagnetic centers in a support material TM and a first optical fiber LWL to which the sensor element NV is attached, wherein the optical fiber LWL transports the pump radiation LB of the pump radiation source PL to the sensor element NV, so that the pump radiation LB irradiates the sensor element NV and the NV centers NVZ or the paramagnetic centers of the sensor element NV emit fluorescence radiation FL, which the optical fiber LWL detects and transports back towards the photodetector PD.

[0050] The optical fiber LWL can be inserted parallel or perpendicular to the axis AX of the permanent magnet PM in the sensor head SK, whereby the sensor element NV is then preferably located in the stray field BSTR of the permanent magnet PM.

[0051] If the return of the fluorescence radiation FL from the sensor element NV to the photodetector PD is to be carried out separately from the supply of the pump radiation LB to the sensor element NV, in this case the sensor head SK preferably comprises a second optical waveguide LWL, which detects fluorescence radiation FL from the sensor element NV and transports the fluorescence radiation FL in the direction of the photodetector PD.

[0052] As explained above, the first optical fiber (OP) and the second OP are preferably identical. This document refers to such an OP as a common optical fiber. Such a common OP saves on calibration effort, reduces assembly complexity, and saves material, thus offering advantages. In particular, it reduces the necessary modifications to the sensor head itself.

[0053] The first optical fiber (OF) has a first end ELWL1 and a second end ELWL2. The second optical fiber (OF) also has a first end ELWL1 and a second end ELWL2. The common optical fiber (OF) likewise has a first end ELWL1 and a second end ELWL2. This document proposes attaching the sensor element NV to the first end ELWL1 of the first optical fiber (OF) and / or the second optical fiber (OF), or the common optical fiber (OF), in order to stabilize the optical coupling between the optical fiber (OF) and the sensor element NV.

[0054] If the first end ELWL1 of the first and / or the second or the common optical fiber LWL is enveloped by the carrier material TM of the sensor element NV, a particularly good stabilization of this optical coupling results.

[0055] Preferably, an end surface EF of the first end ELWL1 of the first and / or the second or the common optical fiber LWL forms a flat end surface EF perpendicular to the center line ML of the optical fiber LWL. The center line ML typically corresponds to the optical axis of the optical fiber LWL. Such a flat end surface EF enables improved coupling of the electromagnetic pump radiation LB from the optical fiber LWL and improved optical coupling of the fluorescence radiation FL into the optical fiber LWL. Preferably, the distance of one or more diamonds or nanodiamonds DM from this flat end surface EF is smaller than the pump radiation wavelength λ. pmp and / or preferably smaller than ½ the pump radiation wavelength λ pmp , and / or preferably smaller than 1 / 4 of the pump radiation wavelength λ pmp , and / or preferably smaller than 1 / 8 of the pump radiation wavelength λ pmp, and / or preferably smaller than 1 / 10 of the pump radiation wavelength λ pmp , and / or preferably smaller than 1 / 20 of the pump radiation wavelength λ pmp , and / or preferably smaller than 1 / 50 of the pump radiation wavelength λ pmp , and / or preferably smaller than 1 / 100 of the pump radiation wavelength λ pmp , , and / or preferably smaller than 1 / 200 of the pump radiation wavelength λ pmp , and / or preferably smaller than 1 / 500 of the pump radiation wavelength λ pmp , and / or preferably smaller than 1 / 1000 of the pump radiation wavelength λ pmp .

[0056] The midline ML, which is an imaginary auxiliary construction to clarify the situation, intersects the end surface EF at a midpoint MP of the end surface EF. The thickness d l The thickness of the carrier material TM is preferentially greater at this center point MP than the thickness d. rat other points on the end surface EF of the first end of the first and / or second or common optical fiber. This has the advantage that light is reflected back through the interface between the carrier material TM and the air into the optical fiber, thus increasing efficiency.

[0057] Preferably, the carrier material TM forms a lens LWLL at the first end ELWL1 of the optical fiber LWL. The diameter D LWLL The lens LWLL is typically smaller than the diameter D. LWL of the optical fiber (OF). The diameter D LWLL The lens LWLL can also be as large as the diameter D LWL of the optical fiber LWL, which, however, is not optimal according to the experience gained in developing the technical teaching of this document.

[0058] Preferably, the first optical fiber (OF) in the area of ​​the sensor head (SC) and / or within the sensor head (SC) is wholly or partially enclosed by a mechanical enclosure (ME). Preferably, the second optical fiber (OF) in the area of ​​the sensor head (SC) and / or within the sensor head (SC) is also wholly or partially enclosed by a mechanical enclosure (ME). Preferably, the common optical fiber (OF) in the area of ​​the sensor head (SC) and / or within the sensor head (SC) is also wholly or partially enclosed by a mechanical enclosure (ME) in the same manner. The mechanical enclosure (ME) supports and protects the respective optical fiber (OF) against the harsh conditions of the respective measurement situation. The mechanical enclosure (ME) within the sensor head (SC) must meet the specific requirements regarding thermal and chemical stability against heat and operating fluids.The mechanical casing MH is therefore preferably made of glass fabric, ceramic, plastic, or the like.

[0059] The mechanical casing MH therefore preferably comprises a ceramic material or another non-magnetizable and / or electrically non-conductive material and / or a material stable at temperatures above 100°C and / or a material stable at temperatures above 140°C and / or a material stable at temperatures above 170°C and / or a material stable at temperatures above 200°C and / or a material stable at temperatures above 250°C, or includes or consists of these materials in the extreme case.The mechanical casing MH can therefore be made of or comprise a ceramic material or another non-magnetizable and / or electrically non-conductive material and / or a material stable at temperatures above 100°C and / or a material stable at temperatures above 140°C and / or a material stable at temperatures above 170°C and / or a material stable at temperatures above 200°C and / or a material stable at temperatures above 250°C.

[0060] Preferably, the mechanical casing MH is at least partially a tube, a capillary, a cannula, or a hose into which the respective optical fiber LWL is inserted. This simplifies the manufacturing of the system consisting of the optical fiber LWL, the sensor element NV, and the mechanical casing MH. The inner diameter D roThe diameter of such a tube or such a small tube or such a capillary or such a cannula or such a hose is preferably only slightly larger than the diameter of the optical fiber lens LWLL and the diameter DLWL of the optical fiber LWL.

[0061] To minimize the ingress of ambient light to the sensor element NV during operation, it is advantageous to completely, partially, or section by section seal the first gap between the edge of the first channel KN and the first optical fiber LWL with an optically opaque filler. For the same reason, it is advantageous to completely, partially, or section by section seal the second gap between the edge of the second channel KN and the second optical fiber LWL with an optically opaque filler, and / or to completely, partially, or section by section seal the common gap between the edge of the common channel KN and the common optical fiber LWL with an optically essentially opaque filler. The common filler can secure the respective optical fiber LWL in the respective channel KN of the sensor head housing GH.

[0062] Preferably, the device is configured to determine the time-dependent intensity profile of the fluorescence radiation FL, particularly in the form of a receiver output signal S0. Furthermore, the device is preferably configured to determine the time-dependent amplitude profile of the intensity of the fluorescence radiation FL from the intensity profile of the fluorescence radiation FL, particularly from the receiver output signal S0, and especially by means of a lock-in amplifier LIV or a functionally equivalent sub-device.

[0063] This document proposes an optical fiber LWL with a sensor element NV for these and other applications with similar measurement tasks. The sensor element NV comprises a substrate TM in which a multitude of diamonds or nanodiamonds DM are embedded. One, more, or all of these diamonds or nanodiamonds DM exhibit one or more NV centers NVZ and / or one or more other paramagnetic centers. The NV centers NVZ of the sensor element NV and / or the other paramagnetic centers of the sensor element NV emit at least one fluorescence radiation FL when irradiated with pump radiation LB. The special feature of the optical fiber LWL proposed in this document is that the substrate TM is preferably a substrate TM cured by electromagnetic radiation and that, after curing, the substrate TM is receptive to radiation with a pump radiation wavelength λ. pmpThe pump radiation LB, with which the NV centers NVZ and / or the other paramagnetic centers are pumped, is essentially transparent. Essentially means that the losses that undoubtedly occur are still so small that the functionality of the application in question is still maintained. Similarly, the support material TM should be transparent to radiation with a fluorescence wavelength λ. fl The fluorescence radiation LB of the NV centers or the paramagnetic centers should be essentially transparent. "Essentially" in this context means that the losses that undoubtedly occur are still so small that the functionality of the application in question is maintained. The production of such an optical fiber (OF) is particularly simple and process-reliable with a high C due to the curing of a previously liquid carrier medium TM. pk -value to manufacture.

[0064] In one variant of the optical waveguide, the diamonds or nanodiamonds (DM) within the substrate (TM) are oriented in substantially different ways relative to each other. This has the advantage that the sensor element behaves isotropically and exhibits no preferred orientation. The mixture of various diamond crystals homogenizes the measurement results and improves the C pk -Value.

[0065] For the same reason, it is advantageous if the orientation of the diamonds or nanodiamonds DM in the carrier material TM is stochastically essentially uniformly distributed.

[0066] Preferably, the optical fiber LWL is configured or designed to transport pump radiation LB from the pump radiation source PL to the sensor element NV, such that the pump radiation LB illuminates the sensor element NV with radiation of the pump radiation wavelength λ. pmp irradiated.

[0067] The optical fiber LWL is preferably also designed or intended to detect fluorescence radiation FL of the sensor element NV and to transport the fluorescence radiation FL towards a photodetector PD.

[0068] The proposed optical fiber LWL preferably has a first end ELWL1 and a second end ELWL2. The carrier material TM preferably forms the sensor element NV and attaches this sensor element NV to the first end ELWL1 of the optical fiber LWL.

[0069] Preferably, the carrier material TM of the sensor element NV encases the first end ELWL1 of the optical fiber LWL. This improves the mechanical connection between the optical fiber LWL and the sensor element NV.

[0070] Preferably, an end surface EF of the first end ELWL1 of the optical fiber LWL forms a planar end surface EF perpendicular to the center line ML of the optical fiber LWL. This improves the coupling of electromagnetic radiation from the core LWLC of the optical fiber LWL into the sensor element NV and vice versa.

[0071] The imaginary virtual center line ML of the optical fiber LWL intersects the end surface EF of the optical fiber LWL at the first end ELWL1 of the optical fiber LWL at a midpoint MP of the end surface EF of the optical fiber LWL. Preferably, the thickness di of the support material TM at this midpoint MP is greater than the thickness d. rat other points on the end face EF of the first end ELWL1 of the optical fiber LWL. This forms an optical functional element at the first end ELWL1 of the optical fiber LWL. This improves the coupling of electromagnetic radiation from the core LWLC of the optical fiber LWL to the sensor element NV and vice versa.

[0072] Preferably, the carrier material TM at the first end ELWL1 of the optical fiber LWL forms a lens LWLL, whose diameter D LWLL preferably smaller than the diameter D LWL of the optical fiber LWL or as large as the diameter D LWL The optical fiber LWL is used. This reduces the measurement volume of the sensor element and thus increases the spatial resolution of magnetic measurements. Therefore, the method presented here, using the proposed device, can detect particularly small cracks RI in the surface OF of the workpiece material.

[0073] Preferably, the first optical fiber (OF) is wholly or partially enclosed by a first mechanical sheath (MH). The mechanical sheath (MH) preferably comprises or incorporates a ceramic material or another non-magnetizable and / or electrically non-conductive material, and / or a material stable at temperatures above 100°C, and / or a material stable at temperatures above 140°C, and / or a material stable at temperatures above 170°C, and / or a material stable at temperatures above 200°C, and / or a material stable at temperatures above 250°C. This protects the sensor element (NV) and the optical fiber (OF) from damage.Preferably, the mechanical casing MH is made of a ceramic material or of another non-magnetizable and / or electrically non-conductive material and / or of a material stable at temperatures above 100°C and / or of a material stable at temperatures above 140°C and / or of a material stable at temperatures above 170°C and / or of a material stable at temperatures above 200°C and / or of a material stable at temperatures above 250°C.

[0074] For improved processing and assembly, the mechanical casing MH preferably comprises at least a section of a tube or conduit or capillary or cannula or hose, in particular a fabric hose.

[0075] The fluorescence radiation of the NV centers NVZ and / or the other paramagnetic centers in the diamonds or nanodiamonds DM of the support material TM and in particular the fluorescence wavelength λ fl The fluorescence radiation FL of these materials can be modified, for example, by plasmonic coupling using metallic nanoparticles that are also added to the support material TM. In this case, the support material TM can then contain metallic nanoparticles with a diameter of less than 200 nm, 100 nm, 50 nm, 20 nm, 10 nm, or 5 nm, which are subsequently embedded in the solidified support material TM. This improves its applicability in specific applications.

[0076] The metallic nanoparticles then typically interact plasmonically with diamonds or nanodiamonds DM in the support material TM and thus influence the fluorescence radiation FL of these diamonds DM.

[0077] These metallic nanoparticles typically contain gold and / or platinum and / or palladium and / or graphite and / or graphene and / or chromium and / or silicon and / or germanium and / or tin and / or sulfur and / or selenium and / or tellurium and / or magnesium and / or calcium and / or strontium and / or barium and / or titanium and / or zirconium and / or hafnium and / or chromium and / or molybdenum and / or tungsten and / or iron and / or ruthenium and / or osmium and / or nickel and / or tin and / or cadmium and / or mercury and / or cerium and / or neodymium and / or samarium and / or gadolinium and / or dysprosium and / or erbium and / or ytterbium and / or thorium and / or proactinium and / or uranium and / or plutonium, with the former being particularly preferred.

[0078] The atoms of the metal in the nanoparticles comprise one or more elements of the periodic table. Each of these elements occurs in nature in various isotopes with a corresponding natural isotopic mixture. Each isotope of an element has a natural proportion corresponding to the natural isotopic mixture of that element. Regarding these proportions and their values, this document refers to the applicant's German patent application DE 10 2020 125 178 A1. These isotopes either have a magnetic nucleus moment µ or do not, depending on the isotope. Preferably, the metallic nanoparticles exhibit an increased proportion in the isotopic mixture for at least one of the following isotopes compared to the natural proportion: 12 C, 14 C, 28 Yes, 30 Yes, 70 Ge,72 Gee, 74 Gee, 76 Gee, 112 Zn, 114 Zn, 116 Zn, 118 Zn, 120 Zn, 122 Zn, 124 Zn 16 ON, 18 ON, 32 WITH, 34 WITH, 36 WITH, 74 Yes, 76 Yes, 78 Yes, 80 Yes, 82 Yes, 120 You, 122 You, 124 You, 126 You, 128 You, 130 You, 24 Mg, 26 Mg, 40 Ca, 42 Ca, 44 Ca, 46 Ca, 48 Ca, 84 Wed, 36 Wed, 88 Wed, 130 Well, 132\ Well, 134 Well, 136 Well, 138 Well, 46 You, 48 You, 50 You, 90 Zr, 90 Zr, 92 Zr, 94 Zr, 96 Zr, 174 Hf, 176 Hf, 178 Hf, 50 Cr, 52 Cr, 53 Cr, 92 Mo, 94 Mo, 96 Mo, 98 Mo,100 Mo, 180 IN, 182 IN, 184 IN, 186 IN, 54 Fe, 56 Fe, 58 Fe, 96 Ru, 98 Ru, 100 Ru, 102 Ru, 104 Ru, 184 Axis, 186 Axis, 188 Axis, 190 Axis, 192 Axis 58 Ni, 60 Ni, 62 Ni, 64 Ni, 102 Pd, 102 Pd, 104 Pd, 106 Pd, 108 Pd, 110 Pd, 190 Fri, 192 Fri, 194 Fri, 196 Fri, 198 Fri 64 Zn, 66 Zn, 68 Zn, 70 Zn, 106 Cont., 108 Cont., 110 Cont., 112 Cont., 114 Cont., 116 Cont., 196 Hg, 198 Hg, 200 Hg, 202 Hg, 204 Hg 136\ Ce, 138 Ce, 140 Ce, 142 Ce, 142 Sun, 144 Sun, 146 Sun, 148 Sun, 150 Sun, 144 Sm, 146 Sm,148 Sm, 150 SM, 152 Sm, 154 Sm, 152 Gd, 154 Gd, 156 Gd, 158 Gd, 160 Gd, 156 Of, 158 Of, 160 Of, 162 Of, 164 Of, 162 On, 164 On, 166 On, 168 On, 170 On, 168 Yb, 170 Yb, 172 Yb, 174 Yb, 176 Yb, 232 Th, 234 If, 234 and, 238 And, 244 PU.

[0079] The optical fiber LWL typically has an optical core LWLC. Within the carrier material TM, an optical functional element is preferably formed at the first end ELWL1 of the optical fiber LWL. This further improves the optical coupling between the optical fiber LWL and the carrier material TM. The optical functional element then interacts optically with the optical core LWLC of the optical fiber LWL at the first end ELWL1 of the optical fiber LWL.

[0080] Preferably, the optical functional element comprises a fiber optic lens LWLL, in particular in the form of a thickening of the carrier material TM in the area of ​​the optical functional element.

[0081] The essential point of this document is that it also describes and discloses a method for manufacturing an optical fiber (OPF) as previously described and used. The proposed method comprises the following steps: • Providing 140 of an optical fiber LWL, wherein the optical fiber LWL has a first end ELWL1 and a second end ELWL2; • Provide 142 of a liquid and cure by means of electromagnetic radiation of a curing wavelength λ Hcurable support material TM, wherein a plurality of diamonds DM, preferably nanodiamonds, are embedded in the support material TM, and wherein one or more or all of these diamonds DM have NV centers NVZ and / or other paramagnetic centers, and wherein the NV centers NVZ of the diamonds DM of the support material TM and / or the other paramagnetic centers of the diamonds DM of the support material TM emit at least one fluorescence radiation FL when irradiated with pump radiation LB; • Wet 145 of the first end of the optical fiber TM over a wetting length L B with the carrier material TM, which features the multitude of embedded diamonds DM; • Injecting 150 electromagnetic radiation into the second end ELWL2 of the optical fiber LWL, where the wavelength of this electromagnetic radiation is the curing wavelength λ H, is chosen such that the carrier material TM at the first end ELWL1 of the optical fiber LWL hardens and transforms into a solid. • Remove 160 of the uncured carrier material TM, in particular by means of a solvent, wherein the remaining film of the carrier material TM at the first end of the optical fiber LWL forms the sensor element NV.

[0082] Typically, the carrier material TM only partially hardens, which allows the formation of the optical functional element.

[0083] The electromagnetic radiation with the curing wavelength λ H exhibits a penetration depth into the carrier material TM such that the carrier material TM is only penetrated to a thickness d l the substrate material hardens and thus forms the optical functional element, which was only recognized as a surprising and advantageous approach during the development of the technical teaching of this document.

[0084] The radiation supplied to the second end ELWL2 of the optical fiber LWL for curing is preferably UV radiation. Radiation with a curing wavelength λ is particularly preferred. H between 320-380nm.

[0085] In certain applications, nanoparticles with a diameter of less than 200 nm, 100 nm, 50 nm, 20 nm, 10 nm, and 5 nm can be added to the carrier material TM before preparation, so that they are embedded in the carrier material TM after curing. Preferably, these are metallic nanoparticles.

[0086] Such metallic nanoparticles interact with diamonds or nanodiamonds DM in the support material TM and can, for example, influence the fluorescence radiation FL of these diamonds or nanodiamonds DM.

[0087] The metallic nanoparticles include, for example, gold and / or platinum and / or palladium and / or graphite and / or graphene and / or chromium and / or silicon and / or germanium and / or tin and / or sulfur and / or selenium and / or tellurium and / or magnesium and / or calcium and / or strontium and / or barium and / or titanium and / or zirconium and / or hafnium and / or chromium and / or molybdenum and / or tungsten and / or iron and / or ruthenium and / or osmium and / or nickel and / or tin and / or cadmium and / or mercury and / or cerium and / or neodymium and / or samarium and / or gadolinium and / or dysprosium and / or erbium and / or ytterbium and / or thorium and / or proactinium and / or uranium and / or plutonium and / or mixtures thereof.

[0088] The atoms of the metal in the nanoparticles naturally comprise one or more elements from the periodic table. Each of these elements occurs in nature in various isotopes with a corresponding natural isotopic mixture. Each isotope naturally contains a proportion corresponding to its natural isotopic mixture. These isotopes may or may not possess a magnetic nucleus µ, depending on the isotope. The metallic nanoparticles exhibit an increased proportion in the isotopic mixture for at least one of the following isotopes compared to the natural proportion: 12 C, 14 C, 28 Yes, 10 Yes, 70 Ge, 72 Ge, 74 Ge, 76 Ge, 112 Zn, 114 Zn, 116 Zn, 118 Zn, 120 Zn, 122 Zn,124 Zn 16 OF, 18 OF, 32 S, 34 S, 36 S, 74 Or, 76 Or, 78 Or, 80 Or, 82 Or, 120 Shall, 122 Shall, 124 Shall, 126 Shall, 128 Shall, 130 Shall, 24 Mg, 26 Mg, 40 Ca, 42 Ca, 44 Ca, 46 Ca, 48 Ca, 84 Sr, 86 Sr, 88 Sr, 130 No, 132 No, 134 No, 136 No, 138 No, 46 Tea, 48 Tea, 50Ti , 90 Zr, 90 Zr, 92 Zr, 94 Zr, 96 Zr, 174 Hf, 176 Hf, 178 Hf, 50 Cr, 52 Cr, 53 Cr, 92 With, 94 With, 96 With, 98 With, 100 with, 18 W, 182 W, 184 W, 186 W, 54 Fe, 56 Fe, 58 Fe, 96 Ru, 98Ru, 100 Ru, 102 Ru, 104 Ru, 184 Axis, 186 Axis, 188 Axis, 190 Axis, 192 Axis 58 Ni, 60 Ni, 62 Ni, 64 Ni, 102 Pd, 102 Pd, 104 Pd, 106 Pd, 108 Pd, 110 Pd, 190 Fri, 192 Fri, 194 Fri, 196 Fri, 198 Fri 64 Zn, 66 Zn, 68 Zn, 70 Zn, 106 Cont., 108 Cont., 110 Cont., 112 Cont., 114 Cont., 116 Cont., 196 Hg, 198 Hg, 200 Hg, 202 Hg, 204 Hg 136 Ce, 138 Ce, 140 Ce, 142 Ce, 142 Sun, 144 Sun, 146 Sun, 148 Sun, 150 Sun, 144 Sm, 146 Sm, 148 Sm, 150 Sm, 152 Sm, 154 Sm, 152 Gd, 154 Gd, 156 Gd, 158 Gd, 160 Gd, 156Dy, 158 Dy, 160 Dy, 162 Dy, 164 Dy, 162 He, 164 He, 166 He, 168 He, 170 He, 168 Yb, 170 Yb, 172 Yb, 174 Yb, 176 Yb, 232 Th, 234 Pa, 234 U, 238 U, 244 Pu. For the purposes of this document, “increased” means that the proportion in the isotopic mixture of the aforementioned isotopes is increased by 50% or more.

[0089] The optical fiber LWL has an optical fiber core LWLC. The proposed method preferably forms the core within the substrate material TM during curing with radiation of the curing wavelength λ. H an optical functional element LWLL at the first end ELWL1 of the optical fiber LWL, wherein the radiation of the curing wavelength λ H The energy is fed in via the second end ELWL2 of the optical fiber LWL and supplied to the carrier material TM.

[0090] The optical functional element LWL, thus shaped, can then optically interact with the optical waveguide core LWLC at the first end ELWL1 of the optical waveguide LWL, if optical radiation, in particular pump radiation LB with the pump radiation wavelength λ, is emitted at the second end ELWL2 of the optical waveguide LWL. pmp is fed in.

[0091] The optical functional element then has a fiber optic lens LWLL, in particular in the form of a thickening of the carrier material TM.

[0092] The document presented here proposes, for example, a clear, colorless, liquid photopolymer, such as Norland Optical Adhesive 61, as the carrier material TM. Further information is available at https: / / www.norlandprod.com / adhesives / noa° / 2061.html at the time of filing of the document presented here.

[0093] Norland Optical Adhesive 61 (“NOA 61”) is a clear, colorless, liquid photopolymer that cures under ultraviolet light. As a 100% solids, one-component system, it offers numerous advantages for bonding applications where the adhesive may be exposed to UV light. Using NOA 61 eliminates the need for premixing, drying, or heat curing, as is common with other adhesive systems. The curing time is short and depends on the applied thickness and the available UV light energy. It is particularly advantageous when the carrier material meets Federal Specification MIL-A-3920 for optical adhesives. NOA 61 meets Federal Specification MIL-A-3920 for optical adhesives. The carrier material is designed to provide the best possible optical bond to glass surfaces, metals, glass fibers, and glass-filled plastics. NOA 61 fulfills this requirement.The use of a substrate material TM is particularly advantageous, as it is recommended for bonding lenses, prisms, and mirrors for military, aerospace, and commercial optics, as well as for terminating and splicing optical fibers. NOA61 meets these requirements.

[0094] The substrate material TM is also characterized by excellent clarity, low shrinkage, and light flexibility. These properties are important so that the user can manufacture high-quality sensor elements NV and achieve long-term performance under changing, aggressive environmental conditions.

[0095] NOA 61 cures, as desired for the substrate TM, with ultraviolet light, with maximum absorption in the range of 320-380 nanometers for the curing wavelength λ. HThe highest sensitivity is achieved at 365 nm. The recommended energy for complete curing is 3 joules / cm². 2 at these wavelengths. Curing is not inhibited by oxygen, so all areas that come into contact with air cure to a non-sticky state when exposed to ultraviolet light.

[0096] In most optical applications, curing occurs in two steps. First, a short, uniform exposure to UV light, known as pre-curing, is applied. This curing time is long enough to solidify the bond and allow it to be moved without affecting its alignment. This is followed by a longer curing phase under UV light to achieve complete crosslinking and solvent resistance of the adhesive. Pre-curing can be achieved in 10 seconds using a 100-watt mercury lamp at 6 inches. If a longer time is required for alignment, this can be extended to several minutes using a very low-intensity light source. Final curing can be achieved in 5 to 10 minutes with the 100-watt mercury lamp.

[0097] Pre-curing allows the user to quickly align and fix the optical fiber (OPF) as needed, minimizing the number of required fixtures. After pre-fixing, excess adhesive can be wiped away with a cloth moistened with alcohol or acetone as an example solvent. The optical fibers should be inspected at this point, and any rejects should be separated in methylene chloride. The coated area of ​​the sensor elements (NV) must be soaked in the solvent and typically dissolves overnight. The time required to dissolve the substrate (TM) depends on the degree of curing and the size of the coating.

[0098] After curing, NOA 61 exhibits very good adhesion and solvent resistance, but it has not yet reached its optimal adhesion to glass. This is achieved through aging for approximately one week, during which a chemical bond forms between the glass and the adhesive. This optimal adhesion can also be achieved by aging at 50°C for 12 hours in a temperature chamber.

[0099] NOA 61 withstands temperatures from -15°C to 60°C before aging when used to coat the optical fiber. After aging, it withstands temperatures from -150°C to 125°C. As a coating on the surface of the optical fiber, NOA 61 withstands 260°C for three hours and during reflow soldering. This allows the sensor element NV to be used for measuring the magnetic flux density B up to these temperatures.The document presented here therefore proposes the use of a proposed optical fiber (OF) at temperatures above 100°C and / or even above 110°C and / or even above 120°C and / or even above 130°C and / or even above 140°C and / or even above 150°C and / or even above 160°C and / or even above 170°C and / or even above 180°C and / or even above 190°C and / or even above 200°C and / or even above 210°C and / or even above 220°C and / or even above 230°C and / or even above 240°C and / or even above 250°C and / or even above 260°C.

[0100] Typical properties of a carrier material are a solids content of more than 80%, a viscosity at 25°C of more than 250 cps, a refractive index of the hardened carrier material TM of more than 1.2, an elongation at break of less than 50% or more than 25% depending on the application, a modulus of elasticity of less than 200,000 psi, a tensile strength of more than 3,000 psi, and a hardness of more than Shore D 60.

[0101] Typical properties of NOA 61 as an exemplary carrier include a solids content of 100%, a viscosity at 25°C of 300 cps, a refractive index of the hardened polymer of 1.56, an elongation at break of 38%, a modulus of elasticity of 150,000 psi, a tensile strength of 3,000 psi, and a hardness of Shore D 85. Advantage

[0102] However, the advantages are not limited to this. • Sensor is galvanically isolated • Diamagnetic measuring head (sensor does not affect measurement) • Insensitive to electrostatic interference • Small measuring volume (fibercore diameter 9µm to 1000µm), variable material thickness at the tip • Measurement frequency DC up to MHz range • Same sensor for DC / AC magnetic field excitation Features of the proposal

[0103] The list of features merely describes preferred dependencies. The technical teaching of this document is not limited to this. Sub-features can also be combined with other features and parts of the description. Such combinations are an explicit part of the disclosure of this document. Feature 1: SK sensor head, with a sensor element NV, wherein the sensor element NV comprises a multitude of diamonds DM and / or nanodiamonds with NV centers NVZ and / or paramagnetic centers and wherein the sensor element NV is located at a first end ELWL1 of an optical fiber LWL and wherein the sensor head SK comprises functional elements of a magnetic circuit and wherein the functional elements of the magnetic circuit comprise at least one source of magnetic excitation H and wherein the sensor head SK has a sensor head housing GH with a contact surface AF and wherein the optical fiber LWL with the sensor element NV in the sensor head housing GH is installed at an angle α to the mounting surface AF of the sensor head SK between 10° and 70° and wherein the sensor element NV is located at a distance from the contact surface AF that is smaller than the diameter of the optical fiber LWL including any mechanical sheath MH of the optical fiber LWL and wherein the optical fiber LWL exits the sensor head housing GH at an angle β to the perpendicular AFS to the contact surface AF of the sensor head SK contact surface AF of 45° to 135° and / or of 70° to 110° and / or of 80° to 100° and / or of 85° to 95° and / or of 87° to 93°. Feature 2: Sensor head SK, with a sensor element NV, wherein the sensor element NV comprises a multitude of diamonds DM and / or nanodiamonds with NV centers NVZ and / or paramagnetic centers and wherein the sensor element NV is located at a first end ELWL1 of an optical fiber LWL and wherein the sensor head SK comprises functional elements of a magnetic circuit and wherein the functional elements of the magnetic circuit comprise at least one source of magnetic excitation H and wherein the functional elements of a magnetic circuit comprise a permanent magnet PM and / or an electric coil as a source of magnetic excitation H and wherein the permanent magnet PM and / or the electrical coil is tubular with an axis AX and wherein the permanent magnet PM is magnetized parallel to the axis AX and / or wherein the electric coil forms its magnetic field parallel to the axis AX when energized and wherein the sensor head SK has a sensor head housing GH with a contact surface AF and wherein the optical fiber LWL with the sensor element NV is installed in the sensor head housing GH and where the sensor element NV is located at a distance from the contact surface AF that is less than the diameter D LWLMH of the sheathed optical fiber LWL is and where the sensor element NV is located on or at least near the extension of the axis AX. Feature 3: Sensor head SK according to feature 2, wherein the sensor head SK comprises a ferromagnetic support ST or another ferromagnetic device element of the sensor head SK, which is different from the permanent magnet PM and / or the electrical coil. Feature 4: Sensor head SK according to feature 3, wherein the ferromagnetic support ST with the permanent magnet PM and / or the electrical coil are device components of a magnetic circuit and where the magnetic excitation H causes a magnetic flux B in the magnetic circuit and wherein this magnetic flux B permeates the sensor element NV and the surface OF of a material of the workpiece, a ferromagnetic material FM of the workpiece, and where spatial fluctuations of the magnetic properties of the workpiece material near the surface OF influence the intensity of a fluorescence radiation FL of the sensor element NV. Feature 5: Sensor head SK according to feature 3 or 4, wherein the ferromagnetic support ST is tubular in shape with a second axis. Feature 6: Sensor head SK according to feature 5, wherein the second axis of the ferromagnetic support ST is essentially parallel to the axis AX of the permanent magnet PM. Feature 7: Sensor head SK according to one of features 3 to 6, wherein the ferromagnetic support ST has an opening OE for the optical fiber LWL in the ferromagnetic support ST; Feature 8: Sensor head SK according to feature 7, where the opening OE is part of a channel KN within the sensor head SK in which the optical fiber LWL is mounted. Feature 9: Sensor head SK according to one of features 3 to 8, wherein the ferromagnetic support ST is filled with at least one filling material of a core KE of the support ST and / or the permanent magnet PM. Feature 10: Sensor head SK according to one of features 3 to 9, wherein the permanent magnet PM is filled with at least one filling material of a core KE of the support ST and / or of the permanent magnet PM. Feature 11: Sensor head SK according to one of features 2 to 10, wherein the sensor element NV comprises a fiber optic lens LWLL and wherein the optical waveguide lens LWLL comprises a multitude of diamonds DM and / or nanodiamonds with NV centers NVZ and / or paramagnetic centers and wherein the optical fiber lens LWLL is located at a first end ELWL1 of the optical fiber LWL and wherein the optical waveguide lens LWLL has a diameter D LWLLthe optical fiber lens LWLL has a diameter smaller than D LWL of the optical fiber LWL. Feature 12: Sensor head SK, with a sensor element NV, wherein the sensor element NV comprises a multitude of diamonds DM and / or nanodiamonds with NV centers NVZ and / or paramagnetic centers and wherein the sensor element NV is located at a first end ELWL1 of an optical fiber LWL and wherein the sensor head SK comprises functional elements of a magnetic circuit and wherein the functional elements of the magnetic circuit comprise at least one source of magnetic excitation H and wherein the functional elements of a magnetic circuit comprise a permanent magnet PM and / or an electric coil as a source of magnetic excitation H and wherein the sensor element NV comprises a fiber optic lens LWLL and wherein the optical waveguide lens LWLL comprises a multitude of diamonds DM and / or nanodiamonds with NV centers NVZ and / or paramagnetic centers and wherein the optical fiber lens LWLL is located at a first end ELWL1 of the optical fiber LWL and wherein the optical waveguide lens LWLL has a diameter D LWLL the optical fiber lens LWLL has a diameter smaller than D LWL of the optical fiber LWL. Feature 13: Sensor head SK according to feature 12, wherein the permanent magnet PM and / or the electrical coil is tubular with an axis AX and wherein the permanent magnet PM is magnetized parallel to the axis AX and / or wherein the electric coil forms its magnetic field parallel to the axis AX when energized. Feature 14: Sensor head SK according to feature 12 or feature 13, wherein the sensor head SK has a sensor head housing GH with a contact surface AF and wherein the optical fiber LWL with the sensor element NV is installed in the sensor head housing GH and where the sensor element NV is located at a distance from the contact surface AF that is less than the diameter D LWLMH of the sheathed optical fiber LWL is and where the sensor element NV is located on or at least near the extension of the axis AX. Feature 15: Sensor head SK according to one of features 12 to 14, wherein the sensor head SK comprises a ferromagnetic support ST or another ferromagnetic device element of the sensor head SK, which is different from the permanent magnet PM and / or the electrical coil. Feature 16: Sensor head SK according to feature 15, wherein the ferromagnetic support ST with the permanent magnet PM and / or the electrical coil are device components of a magnetic circuit and where the magnetic excitation H causes a magnetic flux B in the magnetic circuit and wherein this magnetic flux B permeates the sensor element NV and the surface OF of a material of the workpiece, a ferromagnetic material FM of the workpiece, and where spatial fluctuations of the magnetic properties of the workpiece material near the surface OF influence the intensity of a fluorescence radiation FL of the sensor element NV. Feature 17: Sensor head SK according to feature 15 or 16, wherein the ferromagnetic support ST is tubular in shape with a second axis. Feature 18: Sensor head SK according to feature 17, wherein the second axis of the ferromagnetic support ST is essentially parallel to the axis AX of the permanent magnet PM. Feature 19: Sensor head SK according to one of features 15 to 18, wherein the ferromagnetic support ST has an opening OE for the optical fiber LWL in the ferromagnetic support ST; Feature 20: Sensor head SK according to feature 19, where the opening OE is part of a channel KN within the sensor head SK in which the optical fiber LWL is mounted. Feature 21: Sensor head SK according to one of features 15 to 20, wherein the ferromagnetic support ST is filled with at least one filling material of a core KE of the support ST and / or the permanent magnet PM. Feature 22: Sensor head SK according to one of features 15 to 21, wherein the permanent magnet PM is filled with at least one filling material of a core KE of the support ST and / or of the permanent magnet PM. Feature 23: Method for manufacturing a sensor head SK comprising the steps: Provide 140 of an optical fiber (OF). - wherein the optical fiber LWL has a first end ELWL1 and a second end ELWL2; Providing 145 of a liquid and curing wavelength λ by means of electromagnetic radiation H curable carrier material TM, - wherein the carrier material TM contains a large number of diamonds DM and - wherein one or more or all of these diamonds DM have NV centers NVZ and / or other paramagnetic centers and - wherein the NV centers NVZ of the diamonds DM of the support material TM and / or the other paramagnetic centers of the diamonds DM of the support material TM emit at least one fluorescence radiation FL when irradiated with pump radiation LB; Wetting 150 of the first end ELWL1 of the optical fiber TM over a wetting length LB with the carrier material TM; Injecting 155 electromagnetic radiation into the second end ELWL2 of the optical fiber LWL, - where the wavelength of this electromagnetic radiation is the curing wavelength λ H corresponds, - so that the carrier material TM at the first end ELWL1 of the optical fiber LWL hardens and - so that the carrier material TM at the first end ELWL1 of the optical fiber LWL transforms into a solid and - whereby the hardened carrier material TM then forms the sensor element NV and - wherein the sensor element NV comprises diamonds DM with NV centers NVZ of the diamonds DM and / or with other paramagnetic centers of the diamonds DM which, when irradiated with pump radiation LB, emit at least one fluorescence radiation FL; Removing 160 of the uncured carrier material TM, in particular by means of a solvent, wherein the remaining film of the carrier material TM at the first end ELWL1 of the optical fiber LWL forms the sensor element NV; Providing 165 of a sensor head housing GH of the sensor head SK with a channel KN and an excitation source for a magnetic excitation H, in particular a permanent magnet PM; Installation 170 of the optical fiber LWL with the newly formed sensor element NV into the channel KN of the sensor head housing GH of the sensor head SK and installation of the excitation source for a magnetic excitation H into the sensor head housing GH of the sensor head SK; Use of the SK sensor head 180 for spatially resolved measurement of the magnetic properties of the material of a workpiece near the surface OF of the workpiece, where the distance between the center point MP of the end surface EF of the first end ELWL1 of the optical fiber LWL and the surface OF of the workpiece - smaller than five times the diameter D LWLMH of the sheathed optical fiber LWL and / or - smaller than twice the diameter D LWLMH of the sheathed optical fiber LWL and / or - smaller than the diameter D LWLMH of the sheathed optical fiber LWL and / or - smaller than half the diameter D LWLMH of the sheathed optical fiber LWL. Feature 24: Procedure according to feature 23 where the spatial resolution is better than 500µm and / or better than 200µm and / or better than 100µm and / or better than 50µm and / or better than 20µm and / or better than 10µm and where "resolution" is the possibility of still being able to distinguish two adjacent disturbances of the magnetic properties of a surface OF of a workpiece by an extremum of 5% of the signal amplitude of a flux density measurement signal S4, if these are spaced apart from each other according to the resolution and Such defects can include, for example, cracks, voids, material inhomogeneities, etc. Feature 25: Method for detecting defects, in particular cracks RI or cavities or openings or depressions or material parameter fluctuations, in the surface OF of a magnetically active, in particular ferromagnetic material FM of a workpiece, comprising the steps Placing a sensor head SK, in particular according to one or more of features 1 to 22, with a contact surface AF of the sensor head SK on the surface OF of the workpiece; Moving the sensor head SK on the surface OF of the workpiece parallel to the surface OF of the workpiece along a path x and simultaneously acquiring the values ​​of a flux density measurement signal S4, which depends on the intensity of the fluorescence radiation FL of NV centers NVZ and / or paramagnetic centers in diamonds of a sensor element NV of the sensor head SK; A fault is suspected if the value of the flux density measurement signal S4 deviates locally by more than 25% and / or more than 10% and / or more than 5% and / or more than 1% from the recorded mean value. Feature 26: Procedure according to feature 25, wherein moving the sensor head SK on the surface OF of the workpiece parallel to the surface OF of the workpiece along a path x and simultaneously acquiring the values ​​of the flux density measurement signal S4 includes simultaneously acquiring and / or estimating one or more coordinates of the location of the sensor head SK or an equivalent value at the time of acquiring a value of the flux density measurement signal S4. Feature 27: Procedure according to feature 26, Displaying the values ​​of the flux density measurement signal S4 as a function of the respective recorded coordinates on a screen and / or providing data for such a display. Miscellaneous

[0104] The above description is not exhaustive and does not limit this disclosure to the examples shown. Other variations of the disclosed examples can be understood and carried out by those with ordinary expertise in the field, based on the drawings, the disclosure, and the claims. The indefinite articles "a" or "an" and their inflections do not preclude a plurality, while the mention of a specific number of elements does not preclude the possibility that more or fewer elements are present. A single unit can fulfill the functions of several elements mentioned in the disclosure, and conversely, several elements can fulfill the function of a single unit. Numerous alternatives, equivalents, variations, and combinations are possible without departing from the scope of this disclosure.

[0105] Unless otherwise stated, all features of the present invention may be freely combined with one another. This applies to the entire document presented here. The features described in the figure description may also, unless otherwise stated, be freely combined with the other features of the invention. A restriction of individual features of the exemplary embodiments to combinations with other features of the exemplary embodiments is expressly not intended. Furthermore, material features of the device may be reformulated and used as process features, and vice versa. Such a reformulation is thus automatically disclosed.

[0106] The preceding detailed description refers to the accompanying drawings. The examples in the description and the drawings should be considered illustrative and are not to be regarded as limiting to the specific example or element described. Several examples can be derived from the preceding description and / or the drawings and / or the claims by modifying, combining, or varying certain elements. Furthermore, examples or elements not explicitly described can be derived by a person competent in this regard from the description and / or the drawings. List of characters Fig. Figure 1 shows an exemplary and schematically simplified, proposed material measuring system with a proposed sensor head SK. Fig. Figure 2 shows an optical fiber LWL with a sensor element NV directly on the center MP of the core of the optical fiber LWL. Fig. Figure 3 shows a cross-section through the exemplary first end ELWL1 of a proposed optical fiber LWL. Fig. Figure 4 shows a sensor head SK with the mechanical shell of the optical fiber LWL, which is covered by the mechanical shell MH. Fig. 5 shows the SK sensor head of the Fig. 4 in supervision ( Fig. 5a) and in side view ( Fig. 5b) as a cross-sectional image. Fig. Figure 6 shows the steps of the procedure for manufacturing a proposed sensor head SK and its use. Fig. Figure 7a shows an exemplary workpiece made of a ferromagnetic material FM in a top view. Fig. Figure 7b shows an exemplary value progression of the received measurement signal S4 as a function of the position x of the sensor head SK on the surface OF of the workpiece. Fig. 7a shown. Description of the characters

[0107] The figures illustrate the proposal schematically and in a simplified manner. The disclosure of the text presented here is not limited to the figures and also includes other combinations. Figure 1

[0108] Fig. Figure 1 shows, in a simplified schematic and exemplary manner, an exemplary, proposed material measuring system with a proposed sensor head SK. The sensor head SK comprises the sensor head housing GH. The sensor head housing GH preferably includes a permanent magnet PM. Preferably, the permanent magnet PM is tubular. Preferably, the permanent magnet PM has a permanent magnet symmetry axis AX. Preferably, the permanent magnet PM is magnetized parallel to the permanent magnet symmetry axis AX. The preferably tubular permanent magnet PM typically has a first end and a second end. The second end of the permanent magnet PM has a permanent magnet spacing d. pm from the contact surface AF of the sensor head SK. Since the diameter of the optical fiber LWL is less than 1 mm, the permanent magnet spacing d pmsmaller than 1 mm, better smaller than 0.5 mm, better smaller than 200 pm, better smaller than 100 µm, better smaller than 20 µm. The permanent magnet spacing d pm is preferably slightly larger than the diameter of the optical fiber LWL in the area of ​​the sensor element NV. The permanent magnet spacing d pmThe diameter of the sensor element NV is preferably less than 200% larger than the diameter of the optical fiber LWL, preferably less than 100% larger than the diameter of the optical fiber LWL, preferably less than 50% larger than the diameter of the optical fiber LWL, preferably less than 25% larger than the diameter of the optical fiber LWL, preferably less than 10% larger than the diameter of the optical fiber LWL, and preferably less than 5% larger than the diameter of the optical fiber LWL. Preferably, the material of the housing GH of the sensor head SK is non-magnetic and / or non-magnetizable. For the purposes of this document, a material is considered non-magnetic if its magnetic permeability µ is less than or equal to 0. T this material µ T <1 applies. This document recommends the use of materials with the lowest possible magnetic permeability µ. Tas the material of the sensor head housing GH. Preferably, the sensor element NV is located on the extended axis of symmetry, the permanent magnet symmetry axis AX of the permanent magnet PM.

[0109] For measurement, the operator or a mechanical actuator brings the sensor head SK with its contact surface AF into contact with the surface OF of the workpiece to be measured. Preferably, the surface OF of the workpiece to be measured comprises a ferromagnetic material FM.

[0110] If the workpiece to be measured has a surface OF that exhibits a disturbance which affects the magnetic flux density B, the magnetic flux density B passing through the sensor element NV changes when this disturbance comes close to the permanent magnet symmetry axis AX of the permanent magnet PM and thus close to the sensor element NV. Such a disturbance could be, for example, a crack Ri, a hole, a depression, or any other defect in the workpiece material near the surface OF of the workpiece.

[0111] Generator G produces the transmit pre-signal S5w. Preferably, the transmit pre-signal S5w is pulse-modulated with a pulse frequency. Particularly preferably, it is a square wave signal with a duty cycle of preferably 50%. Other duty cycles are conceivable. The offset addition OFF1 preferably adds an offset to the value of the transmit pre-signal in order to utilize the pump radiation source PL. Preferably, the resulting transmit signal S5 has no negative signal components. The pump radiation source PL generates a modulated pump radiation LB depending on the transmit signal S5. In the example of the Fig. 1. The pump radiation source transmits the pump radiation LB through a dichroic mirror F1 and radiates the pump radiation LB into the optical fiber LWL. The sensor head housing GH has at least one channel KN through which the optical fiber LWL is inserted into the sensor head housing GH. The sensor element NV is preferably located at the first end ELWL1 of the optical fiber LWL. The sensor element NV preferably comprises a plurality of nanodiamonds or diamonds DM, which preferably have a statistically uniformly distributed different crystal orientation and are embedded in a matrix material. Typically, the matrix material, consisting of a carrier material TM, mechanically connects these nanodiamonds ND to the first end ELWL1 of the optical fiber LWL. Preferably, the actual optical fiber LWL has an optical diameter D. LWL of approximately 100 µm. Smaller optical waveguide diameters D are preferred. LWLLarger optical fiber diameters D LWL However, other options are possible. Typically, a kink protector is added to the optical fiber LWL. Preferably, the kink protector is designed as a mechanical sheath MH. The pump radiation LB from the pump radiation source PL strikes the nanodiamonds or diamonds DM in the sensor element NV at the first end ELWL1 of the optical fiber LWL. Preferably, the sensor element NV comprises diamonds with NV centers. Typically, the pump radiation LB excites the nanodiamonds or diamonds DM to emit fluorescence radiation FL with a fluorescence wavelength λ. fl The sensor element NV is preferably located at the first end ELWL1 of the optical fiber LWL. Preferably, the sensor element has a diameter smaller than the diameter D. LWLof the optical fiber LWL. Typically, the NV centers NVZ of the sensor element NV re-emit the fluorescence radiation FL into the optical fiber LWL via the first end ELWL1 of the optical fiber LWL. The fluorescence radiation FL exits the optical fiber LWL at the other, second end ELWL2 of the optical fiber LWL and, for example, deflected by the dichroic mirror F1, preferably illuminates the photodetector PD. The dichroic mirror F1 deflects the scattered pump radiation LB in the example of the Fig. 1 not in the direction of the photodetector PD. As a result, the photodetector PD essentially receives only fluorescence radiation FL. "Essentially" here means that the pump radiation LB and any other radiation that nevertheless reaches the photodetector PD are essentially insignificant for the technical purpose of the device. To achieve this, this document proposes the use of a light-tight housing for the light-sensitive device components and the use of apertures to prevent the ingress of unwanted radiation and undesirable effects from scattered radiation. The photodetector PD preferably converts the intensity of the fluorescence radiation FL into a time-dependent value profile of a received signal S0. An exemplary amplifier V1 amplifies and, if necessary, filters the receiver output signal S0 in the example of the Fig. 1 to the amplified receiver output signal S1. In the example of the Fig. In Figure 1, an exemplary multiplier M1 multiplies the amplified receiver output signal S1 by the transmit pre-signal S5w to produce the filter input signal S3. A low-pass filter TP typically removes the frequency components corresponding to the added frequencies of the transmit pre-signal S5w and the amplified receiver output signal S1 from the spectrum. The low-pass filter TP thus filters the receiver input signal to produce the flux density measurement signal S4. The combination of the first multiplier M1 and the low-pass filter TP forms a scalar product between the signal vector of the amplified receiver output signal S1 and the transmit pre-signal S5w. This is a simple example of a synchronous demodulator. The synchronous demodulator generates a signal S4 that symbolizes the correlation between the amplified receiver output signal S1 and the transmit pre-signal S5w. This signal S4 is the flux density measurement signal S4.The use of other correlators instead of a synchronous demodulator, for example the use of optimal filters, Kalmann filters and / or matched filters, is conceivable. The special feature of the measurement method of the . Fig. 1 is that the optical fiber LWL together with the sensor element NV and the other device parts of the sensor head SK typically does not comprise any ferromagnetic and / or electrically conductive materials and therefore does not substantially influence the magnetic field of the workpiece, or of the ferromagnetic material FM and the permanent magnet PM.

[0112] The intensity of the fluorescence radiation FL of the diamonds DM or nanodiamonds of the sensor element NV depends on the magnetic flux density B at the location of the NV centers NVZ of the sensor element NV. Since the value of the flux density measurement signal S4 indicates how much of the transmit pre-signal S5w is contained in the amplified receiver output signal S1, this flux density measurement signal S4 is a measure of the intensity of the fluorescence radiation FL. Thus, the flux density measurement signal S4 is a measure of the magnetic flux density B at the location of the NV centers NVZ in the sensor element NV.

[0113] In the example of the Fig. In Figure 1, the sensor element NV is positioned in the stray field BSTR of the permanent magnet PM. The ferromagnetic material FM of the workpiece influences this stray field BSTR. If an operator or an actuator now moves the workpiece, and thus the ferromagnetic material FM, along the surface OF of the workpiece on the support surface AF, the influence on the magnetic stray field BSTR changes only if this translational movement at velocity v affects the distribution of physical parameters in the area of ​​the ferromagnetic material influencing the magnetic stray field BSTR. Such an influence can cause a non-uniform distribution of physical parameters in the ferromagnetic material FM, which affects the magnetic stray field BSTR. Preferably, the feed rate v of the sensor head SK relative to the workpiece with the ferromagnetic material FM is constant.Preferably, an operator manually moves the sensor head SK relative to the workpiece at a feed rate v. This document proposes providing an actuator for production testing. This actuator positions the sensor head SK with its contact surface AF on or very close to the surface OF of the workpiece and then moves it parallel to the surface OF of the workpiece along a line to be inspected. Preferably, a computer system uses a coordinate sensor system to determine the position of the sensor head SK, and thus of the sensor element NV, relative to the workpiece and therefore to the ferromagnetic material FM. Preferably, the computer system also records the value of the flux density measurement signal S4 together with the coordinates of the position of the sensor head SK, and thus of the position of the sensor element NV.Preferably, the computer system stores these pairs of coordinates of the measurement point and the measured value of the flux density signal S4 in a memory of the computer system. The computer system can further process this data, for example, to create a two- or three-dimensional model of the distribution of magnetizability. For example, the computer system can determine a two-dimensional distribution of the values ​​of the flux density signal S4 on the surface OF of the workpiece, and thus of the ferromagnetic material FM, and display it on a screen or, for example, as a JPEG image or in a functionally equivalent format. The feed rate v can be 0 m / s for a point measurement. A mechanical housing MH comprising ceramic, a fabric, or a robust plastic protects the common optical fiber LWL. The optical fiber LWL can be fastened in the channel KN of the sensor head housing GH by means of a screw SCHR.An external data bus (EXTDB) enables the CTR half-bridge controller to communicate with a higher-level control system. The external data bus can be a wired or wireless connection. Multiple parallel data connections, implemented in different ways, are possible. Figure 2

[0114] The Fig. Figure 2 shows an optical fiber LWL with a sensor element NV directly on the center MP of the core of the optical fiber LWL. On part of the end face EF of the optical fiber LWL, the sensor element NV is implemented as an optical lens LWLL. Figure 3

[0115] Fig. Figure 3 shows a cross-section through the exemplary first end ELWL1 of a proposed optical fiber LWL. The optical fiber LWL has a core LWLC. The optical fiber LWL can be a single-mode or multi-mode optical fiber. The optical fiber LWL can be a graded optical fiber, a step-index waveguide, or the like, in which the core LWLC transitions smoothly into the outer surface of the optical fiber LWL with respect to the refractive index. The mechanical cladding MH protects the optical fiber LWL and preferably leaves the first end ELWL1 of the optical fiber LWL exposed. The carrier material TM of the sensor element NV surrounds the first end ELWL1 of the optical fiber LWL. The carrier material TM of the optical fiber LWL is preferably transparent to the pump radiation wavelength λ. pmp and the fluorescence wavelength λ flThe transparency here refers to the dimensions of the optical fiber (OF) which has a diameter D. LWL The optical waveguide (OWW) can be smaller than 100 µm. The end surface EF of the OWW is preferably perpendicular to the optical axis of the OWW, which is shown here as the center line ML. At the point where the optical axis intersects the OWW, i.e., the center line ML, an optical waveguide lens LWLL is formed within the substrate TM by thickening the substrate TM. The thickness di of the substrate TM is typically greatest at this point. In the remaining areas of the sensor element NV, the OWW may be thin with a smaller thickness d. r coated with the carrier material TM. The thickness d r It can also be 0m. The diameter D LWLL The optical fiber lens LWLL is typically smaller than the diameter D. LWLof the optical fiber LWL. For clarity, the first end ELWL1 of the optical fiber LWL with the end face EF and the optical fiber lens LWLL on the left is shown enlarged again. The small, stochastically uniformly distributed diamonds or nanodiamonds DM in the substrate material TM are indicated for clarity. Preferably, the diamonds DM nanodiamonds are smaller than 500 µm, better smaller than 200 µm, better smaller than 100 µm, better smaller than 50 µm, better smaller than 20 µm, better smaller than 10 µm, better smaller than 5 µm, better smaller than 2 µm, better smaller than 1 µm, better smaller than 0.5 µm, better smaller than 0.2 µm, better smaller than 0.1 µm, smaller than 50 nm, smaller than 20 nm, and smaller than 10 nm. Sizes above 100 nm are particularly preferred, as sizes smaller than 100 nm can cause special surface effects between the NV center (NVZ) and the diamond surface (DM) of the diamond in question. Preferably, a large number of these diamonds comprise...Nanodiamonds DM have one or more NV centers NVZ and / or one or more paramagnetic centers which then generate fluorescence radiation FL when irradiated with suitable pump radiation LB. Figure 4

[0116] Fig. Figure 4 shows a sensor head SK with the mechanical casing of the optical fiber LWL, which is covered by the mechanical casing MH. The drawing shows the permanent magnet PM. The contact surface AF is at the bottom and hidden. Figure 5

[0117] Fig. 5 shows the sensor head of the Fig. 4 in supervision ( Fig. 5a) and in side view ( Fig. 5b) as a cross-sectional image.

[0118] The mechanical sheath MH of the optical fiber LWL is fixed to the optical fiber LWL in the channel KN of the sensor head housing GH of the sensor head SK by means of a screw SCHR. It is conceivable to fix the mechanical sheath MH of the optical fiber LWL to the optical fiber LWL in the channel KN of the sensor head housing GH of the sensor head SK by means of adhesive bonding. The permanent magnet PM is exemplary implemented as a cylinder. The lower end of the permanent magnet PM has a distance d pm to the contact surface AF. In the example, the contact surface AF is located at the Fig. 5 on the surface OF of the exemplary ferromagnetic material FM of the workpiece. A crack RI is assumed to be present in the ferromagnetic material FM. This crack RI influences the stray field BSTR of the permanent magnet PM. The sensor element NV is located at the first end ELWL1 of the optical fiber LWL. Preferably, the sensor element NV is located near the extension of the axis AX of the cylindrical permanent magnet PM. The crack RI influences the stray field BSTR of the permanent magnet PM in the region of the sensor element NV. Therefore, the crack RI influences the intensity of the fluorescence radiation FL of the NV centers NVZ or paramagnetic centers in the sensor element NV.

[0119] The exemplary sensor head SK has a height of d SK1 The exemplary sensor head SK has a length d SK2 The exemplary sensor head SK has a width of d SK3 .

[0120] On the upper side, opposite the contact surface AF, the sensor head SK has a recess VT with a depth of d. SK4 with respect to the top surface of the sensor head SK. If the sensor head SK is intended for manual positioning on the surface OF of the workpiece, the recess VT preferably has a depth d SK4 Between 3 mm and 1.5 cm, with 5 mm to 8 mm being preferred. This improves handling.

[0121] In the example of the Fig. In section 5, the channel KN has a bend KI at an angle. This has two effects: firstly, it provides a degree of mechanical clamping of the optical fiber LWL within the channel KN, and secondly, it allows the optical fiber LWL to exit the sensor head SK parallel to the contact surface AF. This has the advantage that, due to its flexibility, the optical fiber LWL rests closer to the sensor head SK, for example, on a work surface, than it would without this bend KI. This reduces the torque exerted by the optical fiber LWL on the sensor head SK. Thirdly, this allows the sensor element NV to be positioned closer to the contact surface AF of the sensor head SK. Preferably, the optical fiber LWL forms an angle α with the contact surface AF in the immediate vicinity of the sensor element NV, which is not 90° or 0°. Typically, the angle α lies between 15° and 65°, or preferably between 25° and 55°.Angles α of 30° and 45° are currently in use.

[0122] in the Fig. In figure 5, a ferromagnetic support ST is provided, which conducts the magnetic excitation H of the permanent magnet PM to the workpiece material, here the ferromagnetic material FM. In the example of the Fig. In section 5, the ferromagnetic support ST is an example of a ferromagnetic tube. In this example, the ferromagnetic support ST has the following characteristics: Fig. 5. For example, approximately the same diameter as the permanent magnet PM. In the example of the Fig. Figure 5 shows that the ferromagnetic support ST has an opening OE in its lower region. The optical fiber LWL passes through this opening OE into the interior of the ferromagnetic support ST. This opening OE is thus part of the channel KN in the sensor head housing GH. The ferromagnetic support ST is filled with a core material KE of the support ST and the permanent magnet PM. The channel KN extends from the material of the rest of the sensor head housing GH through the opening OE into this core KE. In the example of the Fig. 5. The rotational symmetry axis AX of the permanent magnet PM coincides with the rotational symmetry axis of the ferromagnetic support ST by way of example. Preferably, the channel KN in the core KE is therefore designed such that, after the insertion of the optical fiber LWL, the sensor element NV is located near the extension of this symmetry axis AX.

[0123] Preferably, the sensor head SK comprises at least one means for generating a magnetic excitation, namely the permanent magnet PM, and a sensor element NV that is connected via at least one optical fiber LWL. The optical fiber LWL is equipped with a control and evaluation device (see Fig. 1) to be connected or is connected to it. The sensor head further comprises a sensor head housing GH made of a non-ferromagnetic material (µ t<1). Preferably, the sensor head SK comprises further functional elements of one or more magnetic circuits. Such a further functional element of one or more magnetic circuits can, for example, be the ferromagnetic support ST. Preferably, the sensor head SK is designed such that the permanent magnet PM and the further functional elements of one or more magnetic circuits of the sensor head SK form at least one common magnetic circuit with a region of the surface OF of a workpiece via a contact surface AF when the sensor head SK is placed with the contact surface AF on the surface OF of the workpiece. Figure 6

[0124] Fig. Figure 6 shows the steps of the procedure for manufacturing a proposed sensor head SK and its use. The procedure comprises the following steps: • Providing 140 of an optical fiber LWL, wherein the optical fiber LWL has a first end ELWL1 and a second end ELWL2; • Providing 145 of a liquid and curing wavelength λ using electromagnetic radiation H curable support material TM, wherein a plurality of diamonds DM or nanodiamonds are embedded in the support material (TM) and wherein one or more or all of the diamonds DM or nanodiamonds of these diamonds DM have NV centers NVZ and / or other paramagnetic centers and wherein the NV centers NVZ of the support material TM and / or the other paramagnetic centers of the support material TM emit at least one fluorescence radiation FL when irradiated with pump radiation LB; • Wet 150 of the first end of the optical fiber TM over a wetting length L B with the carrier material TM, which contains a large number of embedded diamonds DM or nanodiamonds; • Injecting 155 electromagnetic radiation into the second end ELWL2 of the optical fiber LWL, where the wavelength of this electromagnetic radiation is the curing wavelength λ H is chosen such that the carrier material TM at the first end ELWL1 of the optical fiber LWL hardens and transforms into a solid, with the hardened carrier material TM forming the sensor element NV; • Removal of 160 of the uncured carrier material TM, in particular by means of a solvent, wherein the remaining film of the carrier material TM at the first end ELWL1 of the optical fiber LWL forms the sensor element NV; • Providing 165 a sensor head housing GH of the sensor head SK and an excitation source for a magnetic excitation H, in particular a permanent magnet PM; • Installation 170 of the optical fiber LWL with the newly formed sensor element NV into the channel KN of the sensor head housing GH of the sensor head SK and installation of an excitation source for a magnetic excitation H into the sensor head housing GH of the sensor head SK; • Use of the SK sensor head 180 for spatially resolved measurement of the magnetic properties of a workpiece material near the surface OF of the workpiece, where the spatial resolution is better than 500 µm and / or better than 200 µm and / or better than 100 µm and / or better than 50 µm and / or better than 20 µm and / or better than 10 µm. Resolution is defined as the ability to detect two adjacent disturbances in the magnetic properties of a workpiece surface OF with an extremum of 5% of the signal amplitude, provided they are spaced apart according to the resolution. Such disturbances can be, for example, cracks, voids, material inhomogeneities, etc. Figure 7

[0125] Fig. Figure 7a shows an exemplary workpiece made of a ferromagnetic material FM in a top view. Various holes L1 to L3 are drilled into the surface of the workpiece to simulate a crack RI. The first hole L1, for example, has a diameter of 4 mm. The second hole L2 has a diameter of 3 mm. The third hole L3 has a diameter of 2 mm.

[0126] For the creation of the Fig. 7b was fitted with a sensor head SK, as in the Fig. 4 and Fig. 5 shown moved over the surface OF of the workpiece along the path labelled x, maintaining contact between the support surface AF and the surface OF of the workpiece.

[0127] The value profile of the measurement signal S4 obtained in this way is shown in the Fig.Figure 7b shows the position x of the sensor head SK on the surface OF as a function of the position x. Due to the small size D LWL The spatial resolution of the sensor element NV is considerable, which is unknown in the prior art. Reference symbol list 140 Providing 140 of an optical fiber LWL, wherein the optical fiber LWL has a first end ELWL1 and a second end ELWL2; 142 Providing 142 a liquid and curing wavelength λ by means of electromagnetic radiation Hcurable support material TM, wherein a plurality of diamonds DM, preferably nanodiamonds, are embedded in the support material TM, and wherein one or more or all of these diamonds DM have NV centers NVZ and / or other paramagnetic centers, and wherein the NV centers NVZ of the diamonds DM of the support material TM and / or the other paramagnetic centers of the diamonds DM of the support material TM emit at least one fluorescence radiation FL when irradiated with pump radiation LB; 145 Providing 145 a liquid and curing wavelength λ by means of electromagnetic radiation Hcurable support material TM, wherein a plurality of diamonds DM or nanodiamonds are embedded in the support material (TM) and wherein one or more or all of the diamonds DM or nanodiamonds of these diamonds DM have NV centers NVZ and / or other paramagnetic centers and wherein the NV centers NVZ of the support material TM and / or the other paramagnetic centers of the support material TM emit at least one fluorescence radiation FL when irradiated with pump radiation LB; 150 Wet 150 of the first end of the optical fiber TM over a wetting length L B with the carrier material TM, which contains a large number of embedded diamonds DM or nanodiamonds; 155 Injecting 155 electromagnetic radiation into the second end ELWL2 of the optical fiber LWL, wherein the wavelength of this electromagnetic radiation is the curing wavelength λ His chosen such that the carrier material TM at the first end ELWL1 of the optical fiber LWL hardens and transforms into a solid, with the hardened carrier material TM forming the sensor element NV; 160 Removal 160 of the uncured carrier material TM, in particular by means of a solvent, wherein the remaining film of the carrier material TM at the first end ELWL1 of the optical fiber LWL forms the sensor element NV; 165 Providing a sensor head housing GH of the sensor head SK and an excitation source for a magnetic excitation H, in particular a permanent magnet PM; 170 Installation of the optical fiber LWL with the newly formed sensor element NV into the channel KN of the sensor head housing GH of the sensor head SK and installation of an excitation source for a magnetic excitation H into the sensor head housing GH of the sensor head SK; 180 Use of the SK sensor head for spatially resolved measurement of the magnetic properties of a workpiece material near the surface OF of the workpiece, where the spatial resolution is better than 500 µm and / or better than 200 µm and / or better than 100 µm and / or better than 50 µm and / or better than 20 µm and / or better than 10 µm. Resolution is defined as the ability to distinguish two adjacent disturbances in the magnetic properties of a workpiece surface OF by an extremum of 5% of the signal amplitude, provided they are spaced apart according to the resolution. Such disturbances can be, for example, cracks, voids, material inhomogeneities, etc. α Angle formed by the optical fiber LWL with the contact surface AF in the immediate vicinity of the sensor element NV; β is the angle between the virtual perpendicular AFS to the contact surface AF of the sensor head SK on the one hand, and the optical fiber LWL at its exit from the sensor head housing GH of the sensor head SK on the other. Preferably, the angle β is 90°. This has the advantage that such an angle β minimizes the torque that the optical fiber LWL, together with its mechanical casing MH, exerts on the sensor head SK, since the optical fiber LWL then comes to rest at a relatively short distance from the sensor head SK on the surface of the workpiece or a surface on which the workpiece rests. Preferably, the value of β is between 45° and 135°, better between 70° and 110°, better between 80° and 100°, better between 85° and 95°, better between 87° and 93°. AX permanent magnet symmetry axis; AF contact surface of the sensor head SK; AFS virtual perpendicular to the contact surface AF of the sensor head SK; B magnetic flux density; BSTR magnetic stray field of the magnetic flux density of the permanent magnet PM; d l Thickness of the carrier material TM at the center MP of the end face EF at the first end ELWL1 of the first and / or second or common optical fiber LWL; d pm distance d pm of the lower end of the permanent magnet PM to the contact surface AF; d r Thickness at other points of the end surface EF of the first end ELWL1 of the first and / or the second or the common optical fiber LWL; d SK1 Height of the sensor head SK; d SK2 SK sensor head length; d SK3 SK sensor head width; d SK4 Depth of the recess VT of the sensor head SK; D LWL Diameter of the optical fiber (OF) D LWLL Diameter of the optical waveguide lens LWLL; D LWLMHDiameter of the encased optical fiber LWL comprising the diameter of the optical fiber LWL with the mechanical cladding MH; DM Diamonds DM. The diamonds preferably have a size of less than 5mm, better less than 2mm, better less than 1mm, better less than 0.5mm, better less than 0.2mm, better less than 0.1mm, better less than 50µm, better less than 20µm, better less than 10µm, better less than 5µm, better less than 2mm, better less than 1µm, better less than 0.5µm, better less than 0.2µm, better less than 0.1µm, better less than 50nm, better less than 20nm, better less than 10nm; EF end surface of the first end ELWL1 of the first and / or the second or the common optical fiber LWL; ELWL1 first end of the optical fiber LWL; ELWL2 second end of the optical fiber LWL; F1 dichroic mirror; FL Fluorescence radiation; FM ferromagnetic material; G Signal generator; GH sensor head housing. The sensor head housing can be manufactured, for example, by 3D printing, such as FDM or SLS printing. Preferably, the material of the sensor head housing is non-ferromagnetic (µ) at least in the vicinity of the sensor element NV. t <1). Preferably, the material of the sensor head housing is diamagnetic; GND reference potential; H magnetic excitation; AI kink in the channel KN of the sensor head housing GH; KN channel KN, through which the optical fiber LWL is inserted into the sensor head housing GH; L B Wetting length; LB Pump radiation; LIV Lock-In Amplifier; Fiber optic cable. Preferably, this is a single optical fiber; LWLC core of the optical fiber LWL; LWLL optical fiber lens; λ fl Fluorescence wavelength; λ H Curing wavelength; λ pmpPump radiation wavelength; M1 Multiplier; MH mechanical casing; ML center line of the optical fiber (this is a virtual line); MP center of the end face EF of the first end ELWL1 of the optical fiber LWL; NV sensor element. Preferably, the sensor element comprises a plurality of nanodiamonds or diamonds DM, which are oriented differently and preferably have a plurality of NV centers NVZ. Preferably, the sensor element with the diamonds DM or nanodiamonds is positioned centrally under the permanent magnet PM and as close as possible to the test object, here the exemplary workpiece with the ferromagnetic material FM; NVZ NV centers; KE Core<<< KN channel in the sensor head housing GH for the supply of the optical fiber LWL and / or optical window in the sensor head housing GH; OE opening for the optical fiber LWL in the ferromagnetic support ST; OF surface of the workpiece, for example the surface of a ferromagnetic material FM; OFF1 Offset Addition; PD photodetector; PL pump radiation source; PM permanent magnet. Preferably, the permanent magnet is tubular with a permanent magnet symmetry axis AX. If the sensor element NV is located on this symmetry axis AX, the horizontal component of the magnetic flux density B is approximately 0 T. In the example presented here, the permanent magnet serves to provide the magnetic excitation H of the magnetic circuit of the sensor head SK in conjunction with the workpiece material near the workpiece surface OF and near the sensor element NV. Instead of a permanent magnet, a current-carrying coil or the like can also be used. More complex magnetic circuits with more than one source of magnetic excitation are also conceivable. For example, the sensor head SK can also comprise a combination of one of the several permanent magnets with one or more coils as the source of the magnetic excitation H.For example, the sensor head SK can also have one or more coils as the source of magnetic excitation H. For the purposes of this document, the term permanent magnet refers to any arbitrarily structured source of magnetic excitation H. However, a single permanent magnet is expressly preferred. RI is a defect in the ferromagnetic material FM. Such a defect can be a change in composition that locally alters the magnetic properties of the ferromagnetic material FM. For example, it can be a crack, a void, a hole, a depression, a thickness variation, or a modulation of a form factor such as thickness, width, or the like. S0 receiver output signal; S1 amplified receiver output signal; S3 filter input signal; S4 flux density measurement signal; S5 transmit signal; S5w transmit pre-signal; SCHR screw. The sensor head housing GH preferably has a thread for a setscrew to fix the optical fiber LWL; SK sensor head; ST ferromagnetic support; t time; TM Carrier material; TP low-pass filter or filter with low-pass properties; v feed rate; V1 Amplifier; VDD supply voltage; VT Recess VT of the sensor head SK e.g. for a guide finger of a hand; List of cited works DE 10 2019 120 076 A1, DE 11 2020 003 569 A5, DE 11 2020 004 650 A5, DE 10 2020 109 477 A1 DE 10 2021 101 565 A1, DE 10 2021 114 589.9, DE 10 2022 121 444.3, DE 10 2022 122 505.7, EP 3 874 343 A2

Claims

[1] Method for manufacturing a sensor head (SK) comprising the steps: Provision (140) of an optical fiber (OF), - wherein the optical fiber (OF) has a first end (OF1) and a second end (OF2); Providing (145) a liquid and curing wavelength (λ) by means of electromagnetic radiation H ) curable carrier material (TM), - wherein the carrier material (TM) contains a multitude of diamonds (DM) and - wherein one or more or all of these diamonds (DM) have NV centers (NVZ) and / or other paramagnetic centers and - wherein the NV centers (NVZ) of the diamonds (DM) of the support material (TM) and / or the other paramagnetic centers of the diamonds (DM) of the support material (TM) emit at least one fluorescence radiation (FL) when irradiated with pump radiation (LB); Wetting (150) the first end (ELWL1) of the optical fiber (TM) to a wetting length (L B ) with the carrier material (TM); Feeding (155) electromagnetic radiation into the second end (ELWL2) of the optical fiber (LWL), - where the wavelength of this electromagnetic radiation is the curing wavelength (λ) H ) corresponds, - so that the carrier material (TM) at the first end (ELWL1) of the optical fiber (OF) hardens and - so that the carrier material (TM) at the first end (ELWL1) of the optical fiber (OF) transforms into a solid and - wherein the hardened carrier material (TM) then forms the sensor element (NV) and - wherein the sensor element (NV) then comprises diamonds (DM) with NV centers (NVZ) of the diamonds (DM) and / or with other paramagnetic centers of the diamonds (DM) which, when irradiated with pump radiation (LB), emit at least one fluorescence radiation (FL); Removal (160) of the uncured carrier material (TM), in particular by means of a solvent, wherein the remaining film of the carrier material (TM) at the first end (ELWL1) of the optical fiber (LWL) forms the sensor element (NV); Providing (165) a sensor head housing (GH) of the sensor head (SK) with a channel (KN) and an excitation source for magnetic excitation (H), in particular a permanent magnet (PM); Installation (170) of the optical fiber (OF) with the newly formed sensor element (OF) into the channel (OF) of the sensor head housing (SH) of the sensor head (SH) and installation of the excitation source for a magnetic excitation (H) into the sensor head housing (SH) of the sensor head (SH); Use (180) of the sensor head (SK) for spatially resolved measurement of the magnetic properties of the material of a workpiece near the surface (OF) of the workpiece, where the distance between the center point (MP) of the end face (EF) of the first end (ELWL1) of the optical fiber (OF) and the surface (OF) of the workpiece - smaller than five times the diameter (D LWLMH ) of the sheathed optical fiber (OF) and / or - smaller than twice the diameter (D LWLMH ) of the sheathed optical fiber (OF) and / or - smaller than the diameter (D LWLMH ) of the sheathed optical fiber (OF) and / or - smaller than half the diameter (D LWLMH ) of the sheathed optical fiber (OF). [2] Method according to claim 1 where the spatial resolution is better than 500µm and / or better than 200µm and / or better than 100µm and / or better than 50µm and / or better than 20µm and / or better than 10µm and where "resolution" is the ability to distinguish two adjacent disturbances of the magnetic properties of a surface (OF) of a workpiece by an extremum of 5% of the signal amplitude of a flux density measurement signal (S4), if these are spaced apart according to the resolution and Such defects can include, for example, cracks, voids, material inhomogeneities, etc.

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