DE102022131305B4 - Sensor head for high spatial resolution, purely optical and wireless measurement of magnetic material properties on the surface of a workpiece - Google Patents

Abstract

The invention relates to a sensor head SK for measuring the material properties of ferromagnetic surfaces with a sensor element NV that comprises diamonds with NV centers NVZ. The sensor element NV is located at a first end ELWL1 of an optical fiber LWL. The sensor head SK comprises functional elements of a magnetic circuit that comprise at least one source of magnetic excitation H, in particular a permanent magnet PM that is tubular with an axis AX. The sensor head SK has a sensor head housing GH with a support surface AF, in which the optical fiber LWL with the sensor element NV is installed in the sensor head housing GH. The sensor element NV is located at a distance from the support surface AF that is smaller than the diameter of the optical fiber LWL including any mechanical sheath MH of the optical fiber LWL. The sensor element NV is located near the extension of the axis AX.

Description

Field of invention

The invention is directed to a sensor head for the highly spatially resolved 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 one another and to the sensor head housing, and wherein diamonds of these diamonds comprise NV centers or other paramagnetic centers.

General introduction

A recurring problem is the detection of cracks and other defects in the surfaces of ferromagnetic workpieces. The state of the art does indeed contain appropriate measuring methods. However, these only show insufficient spatial resolution to detect small cracks.

The document presented here provides only brief points on the principles of non-destructive testing of materials with regard to the state of the art.

When measuring workpieces using magnetic field measurement, the use of Hall sensors/coils to measure magnetic stray fields/eddy current fields results in the problems that these measuring methods have a large measuring volume at a limited distance to the workpiece and a large measuring cross-section. The corresponding devices are not diamagnetic and therefore change the measuring object, the magnetic field.

The method and device presented here are intended to remedy this.

State of the art

From the EN 10 2019 120 076 A1 , the EN 11 2020 003 569 A5 , the EN 11 2020 004 650 A5 , the EN 10 2021 101 565 A1 and the EP 3 874 343 A2 Wireless devices for detecting magnetic fields are already known.

From the EN 10 2020 109 477 A1 Methods for producing NV centers are known.

Further properties are known from the still unpublished German patent application EN 10 2021 114 589.9 known.

From the still unpublished German patent application EN 10 2022 121 444.3 The commutation of an electric motor by means of a wireless magnetic field measurement is known.

From the still unpublished German patent application EN 10 2022 122 505.7 The production of a suitable optical waveguide is known.

From the Scripture WO 2022 096 891 A1 A sensor is known which comprises a magnet. According to the technical teaching of WO 2022 096 891 A1 The magnet is arranged in such a way that it applies an inhomogeneous magnetic field to a certain volume. The sensor of the WO 2022 096 891 A1 further comprises a magnetometer having an active element for detecting the magnetic field in a volume comprising the specific volume.

From the Scripture CN114 994 006 A is a detection system for orthogonal cracks based on the NV color center detection technology. The detection system of the CN1 14 994 006 A comprises an excitation end, a collecting end and a magnetization detection front end. The technical teaching of the CN1 14 994 006 A uses the excitation end to generate excitation light, the excitation light acting on the front end of the magnetization sensor. The front end of the magnetization sensor comprises a magnetization part and a detection part, the magnetization part being used to magnetize a ferromagnetic object to be detected. The magnetization part of the device of the CN114 994 006 A comprises a magnetization interval. If a crack on the ferromagnetic object to be detected is positioned in the magnetization interval, the device can CN114 994 006 A generate a magnetic stray field at the crack. The detection part of the device of the CN114 994 006 A generates a voltage fluorescence under the action of the excitation light and the magnetic stray field. The detection part of the device of the CN114 994 006 A is used to receive the voltage fluorescence and to analyze and process the voltage fluorescence. The magnetization part of the CN114 994 006 A comprises two groups of electromagnets. The magnetization directions of the two groups of electromagnets of the device of the CN1 14 994 006 A are orthogonal to each other. The sensor part of the device of the CN1 14 994 006 A comprises an optical sensor fiber, an end portion of the optical sensor fiber is a detection end, and diamond-shaped NV colorant particles attached to the fiber core are arranged on the end face of the detection end.

• Schritt 1) Mischen der Lösung mit einer wässrigen Nano-Diamantpartikel-Lösung, die NV-Farbzentren enthält;
• Schritt 2) Auflösen der hergestellten Lösung, die mit den Nano-Diamantpartikeln, die die NV-Farbzentren enthalten, dotiert ist, mit Ultraschall durch ein Sol-Gel-Verfahren, Versiegeln und Stehenlassen der Lösung und vollständiges Hydrolysieren der Lösung, um Sol-Gel zu bilden; und 3) gleichmäßiges Auftragen des in Schritt 2) hergestellten Sol-Gels auf die Endfläche der optischen Faser, Halten der optischen Faser durch einen Schrittmotor, Kontaktieren der Endfläche der optischen Faser mit dem Sol-Gel, Ziehen der Endfläche der optischen Faser mit einer bestimmten Geschwindigkeit nach einer Zeitspanne, um einen halbkugelförmigen Gelfilm mit einer bestimmten Dicke und einer bestimmten Krümmung zu bilden, und Aushärten, um die hergestellte Quantensonde der optischen Faser zu erhalten. Laut der technischen Lehre der CN 1 12 146 782 A kann die Dotierungskonzentration der Nanodiamantteilchen, die NV-Farbzentren enthalten, gesteuert werden. Laut der technischen Lehre der CN 1 12 146 782 A sind die Nanodiamantteilchen gleichmäßig gemischt. Die Schrift CN 1 12 146 782 A gibt an, dass der Herstellungsprozess der Sonde einfach ist, seine Wiederholbarkeit ist hoch ist und dass eine Massenproduktion realisiert werden kann.

From the Scripture CN 1 12 146 782 A A method for producing a fiber optic quantum probe with controllable diamond particle doping is known. The method of CN 1 12 146 782 A includes 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 the nano diamond particles containing the NV color centers with ultrasonics by a sol-gel method, sealing and allowing the solution to stand, and completely hydrolyzing the solution to form sol-gel; and 3) uniformly applying the sol-gel prepared in step 2) onto the end face of the optical fiber, holding the optical fiber by a stepping motor, contacting the end face of the optical fiber with the sol-gel, pulling the end face of the optical fiber at a certain speed after a period of time to form a hemispherical gel film with a certain thickness and a certain curvature, and curing to obtain the prepared optical fiber quantum probe. According to the technical teaching of CN 1 12 146 782 A the doping concentration of the nanodiamond particles containing NV color centers can be controlled. According to the technical teaching of CN 1 12 146 782 A the nanodiamond particles are evenly mixed. The writing CN 1 12 146 782 A states that the manufacturing process of the probe is simple, its repeatability is high and that mass production can be realized.

From the Scripture CN 1 14 720 553 A A device for detecting leakage flux in a pipeline is known. The device of the CN 1 14 720 553 A is based on an optical fiber that couples a diamond nitrogen vacancy color center.

Task

The proposal is therefore based on the task of creating a solution which does not have the above-mentioned disadvantages of the prior art and has further advantages.

This problem is solved by the first claim and the parallel claims.

Solution to the task

• • dass der Sensorkopf NV-reichen Diamantstaub als Magnetfeldsensor verwendet und
• • dass Permanentmagnete oder -spulen (AC oder DC Magnetfelder) des Sensorkopfes ein magnetisches Prüffeld erzeugen, das in die Oberfläche des Werkstücks eindringt, und
• • dass das Diamantmaterial des Diamantstubs an einem Faserende eines Lichtwellenleiters das Sensorelement bildet und
• • dass der Sensorkopf eine rein optische Vermessung des Magnetfelds und damit der magnetischen Eigenschaften der Oberfläche des Werkstücks über den Lichtwellenleiter ermöglicht.

In a sensor head of the proposed type, the task is solved according to the proposal by

• • 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 fiber end of an optical fiber and
• • that the sensor head enables a purely optical measurement of the magnetic field and thus of the magnetic properties of the surface of the workpiece via the optical fiber.

The present document proposes a device for detecting the magnetic flux density B in the vicinity of a disturbance of a ferromagnetic surface.

The sensor head SK has a sensor element NV with a carrier TM. A large number of diamonds DM are preferably embedded in the carrier TM. The carrier material TM preferably comprises glass and/or a hardened plastic. The carrier material TM fixes the diamonds DM and prevents repositioning of the diamonds DM. After solidification in the manufacturing process, the carrier material TM is preferably transparent to the pump wavelength λ _pmp of the pump radiation LB and to the fluorescence radiation FL of the NV centers in the diamonds DM. One or more or all diamonds DM of these diamonds DM typically have 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 causes a reduction in the intensity of the fluorescence radiation FL. The sensor head SK preferably has an optical fiber LWL to allow pump radiation LB from a pump radiation source PL to reach the sensor element NV. The pump radiation LB preferably has a pump radiation wavelength λ _pmp in a wavelength range of 400 nm to 700 nm wavelength and/or better 450 nm to 650 nm and/or better 500 nm to 550 nm and/or better 515 nm to 540 nm. A wavelength of 532 nm is clearly preferred as the pump radiation wavelength λ _pmp . In the case of NV centers in diamond or in diamonds, a laser diode from Osram of the type PLT5 520B is suitable, for example, as a pump radiation source PL1 with a 520 nm pump radiation wavelength λ _pmp . The NV centers NVZ of the sensor element NV typically emit a fluorescence radiation FL with a typical fluorescence wavelength λ _fl of approximately 637 nm at NV centers when irradiated with pump radiation LB of the pump radiation wavelength λ _pmp described above. Other wavelengths can by plasmonic coupling with metallic nanocrystals in the carrier material TM. The optical properties of the NV centers can be modified by combining the nanodiamonds or diamonds DM in the carrier 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 also has 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, if possible, no pump radiation LB falls 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 _fl of the fluorescence radiation FL - e.g. 637 nm at NV centers NVZ with a phonon sideband from 637 nm to 850 nm - in the direction of the photodetector PD, while it does not allow the radiation with the pump radiation wavelength λ _pmp of the pump radiation LB of the pump radiation source PL and thus the modulated pump radiation LB to pass or guides it in such a way that it does not hit or influence the photodetector PD. The photodetector PD converts the intensity signal of the fluorescence radiation FL into a receiver output signal SO. 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.

The proposed device has the advantage that the magnetic field of the cracks RI and/or depressions in the surface of a ferromagnetic material FM is not disturbed by supply lines, such as when measuring magnetic fields with Hall sensors. Furthermore, the sensor element NV is completely diamagnetic. A reaction of the magnetic fields and/or interference fields on the evaluation electronics of the sensor system via the sensor element NV and the optical fiber LWL is very unlikely due to the galvanic isolation. This means that the system can also be used in high-voltage systems with device parts that are driven with very high voltages. Systems from the state of the art do not show this.

In one variant, the diamonds DM in the carrier material TM are essentially oriented differently from one another, each with a substantially different orientation. 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 use, for example, diamond powder with 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 records the amount of the magnetic flux density B, but not the direction. This has the advantage that alignment of the sensor element NV and 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 assistants or less precise mechanical devices, which only have 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. In order to achieve spatial isotropy, it is therefore advantageous if the orientation of the diamonds DM is stochastically essentially uniformly distributed.

In the course of developing the technical teaching of this document, the applicant recognized that, in accordance with the preceding statements, 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. Instead of a permanent magnet, other field excitations are conceivable. These are included in the description "permanent magnet PM" in the sense of the document presented here.

In order to minimize the number of optical fibers LWL and to keep the modifications to the sensor head SK to a minimum, it is advantageous to use a single optical fiber LWL 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 optical fiber LWL, so that the first channel KN is identical to the second channel KN. The following text then refers to such a channel KN as a common channel KN.

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 waveguide LWL to which the sensor element NV is attached, wherein the optical waveguide 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 waveguide LWL detects and transports back in the direction of the photodetector PD.

The optical waveguide LWL can be inserted parallel to the support surface AF of the sensor head SK, whereby the sensor element NV is then preferably located in the stray field of the cracks RI and/or depressions in the surface of a ferromagnetic material FM. The optical waveguide LWL can also be inserted into the sensor head perpendicular to the support surface AF of the sensor head SK using a vertical channel and pushed forward into the vicinity of the support 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 pushed forward into the immediate vicinity of the support surface AF of the sensor head SK, but this then creates the problem that the probability of damage to the sensor head SK during measurement operation increases due to a movement along the support surface AF of the sensor head SK.

If the return of the fluorescence radiation FL from the sensor element NV to the photodetector PD is to take place 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 the fluorescence radiation FL of the sensor element NV and transports the fluorescence radiation FL in the direction of the photodetector PD.

As stated above, however, the first optical fiber LWL is preferably identical to the second optical fiber LWL. The document presented here refers to such an optical fiber LWL as a common optical fiber LWL. Such a common optical fiber LWL saves calibration effort and reduces assembly complexity and saves material and is therefore advantageous. In particular, the necessary modifications to the sensor head SK itself are reduced.

The first optical waveguide LWL has a first end and a second end. The second optical waveguide LWL also has a first end and a second end. The common optical waveguide LWL also has a first end and a second end. The document presented here now proposes attaching the sensor element NV to the first end of the first optical waveguide LWL and/or second optical waveguide LWL or the common optical waveguide LWL in order to stabilize the optical coupling between the optical waveguide LWL and the sensor element NV.

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

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

The center line ML, which is an imaginary auxiliary construction to clarify the situation, penetrates the end surface EF at a center point MP of the end surface EF. The thickness dl of the carrier material TM is preferably thicker at this center point MP than the thickness dr at other points of the end surface EF of the first end of the first and/or the second or the common optical waveguide LWL. This has the advantage that light is reflected back into the optical waveguide LWL through the interface between the carrier material TM and air, and that the efficiency and effectiveness then increase.

The carrier material TM therefore preferably forms a lens LWLL at the first end ELWL1 of the optical waveguide LWL. The diameter DLWLL of the lens LWLL is typically smaller than the diameter DLWL of the optical waveguide LWL. The diameter DLWLL of the lens LWLL can also be as large as the diameter DLWL of the optical waveguide LWL, but this is not optimal based on experience in preparing the technical teaching of this document.

Preferably, the first optical waveguide LWL in the area of the sensor head SK and/or within the sensor head SK is completely or partially by a mechanical sheath MH. Preferably, the second optical fiber LWL in the area of the sensor head SK and/or within the sensor head SK is also completely or partially covered by a mechanical sheath MH. Preferably, the common optical fiber LWL in the area of the sensor head SK and/or within the sensor head SK is completely or partially covered in the same way by a mechanical sheath MH. The mechanical sheath MH supports and protects the respective optical fiber LWL against the harsh conditions inside and outside the sensor head SK. The mechanical sheath MH within the sensor head SK must generally meet special requirements with regard to thermal and chemical stability against heat and operating fluids. The mechanical sheath MH is therefore preferably made of glass or ceramic or the like. Most preferably, the mechanical sheath comprises a mechanically flexible material, for example a fabric, for example a glass fabric.

The mechanical casing MH therefore preferably comprises a ceramic material or another non-magnetizable and/or electrically non-conductive material and/or a material that is stable at temperatures above 100°C and/or a material that is stable at temperatures above 140°C and/or a material that is stable at temperatures above 170°C and/or a material that is stable at temperatures above 200°C and/or a material that is stable at temperatures above 250°C or comprises these or, in extreme cases, consists of these. This means that the sensor head can also be used 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.

Preferably, the mechanical sheath MH is at least partially a tube or a small tube or a capillary or a cannula, into which the respective optical waveguide LWL can be pushed, for example. This simplifies the manufacture of the system comprising optical waveguide LWL, sensor element NV and mechanical sheath MH. The inner diameter Dro of such a tube or such a small tube or such a capillary or such a cannula is preferably only slightly larger than the diameter of the optical waveguide lens LWLL and the diameter DLWL of the optical waveguide LWL.

In order to minimize the access of extraneous light to the sensor element NV during operation, it is useful if the first gap between the edge of the channel KN and the first optical fiber LWL is completely or partially closed with an optically opaque filling compound FM. For the same reason, it is useful if the second gap between the edge of the second channel KN and the second optical fiber LWL is completely or partially closed with an optically opaque filling compound FM and/or if the common gap between the edge of the channel KN and the common optical fiber LWL is completely or partially closed with an optically essentially opaque filling compound FM. The common filling compound FM can attach the respective optical fiber to the housing of the sensor head SK.

The device is preferably designed to determine the temporal value profile of the intensity of the fluorescent radiation FL, in particular in the form of a receiver output signal S0. Furthermore, the device is preferably designed to determine the temporal value profile of the amplitude value of the temporal value profile of the intensity of the fluorescent radiation FL from the temporal value profile of the intensity of the fluorescent radiation FL, in particular from the receiver output signal S0 and in particular by means of a lock-in amplifier LIV or a functionally equivalent sub-device. Finally, the device is preferably designed to provide a display or other signaling depending on the determined temporal value profile of the amplitude value of the temporal value profile of the intensity of the fluorescent radiation FL.

Preferably, the device according to the proposal is designed to determine, in particular by means of a high-pass filter or a functionally equivalent filter, an alternating component and/or a 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.

Preferably, the device is designed to determine, in particular by means of a second low-pass filter TP2, a low-frequency DC component in the temporal progression of the amplitude value of the temporal progression 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 determine deviations from expected values. To do this, the device compares the value of the DC component with an expected value interval. If the value of the DC component is outside the expected value interval, the device preferably concludes that there is an error and initiates appropriate measures. One such measure can be, for example, that the half-bridge control CTR transmits a signal to a higher-level computer system via an external data bus EXTDB, which then initiates everything else.

Preferably, the device is designed to separate this low-frequency direct component in the temporal progression of the amplitude value of the temporal value progression of the intensity of the fluorescence radiation FL from the temporal progression of the amplitude value of the temporal value progression of the intensity of the fluorescence radiation FL and thus to determine the alternating component of the temporal progression of the amplitude value of the temporal value progression of the intensity of the fluorescence radiation FL.

An example application of the proposed optical waveguide LWL is the measurement of a magnetic field of a ferromagnetic material FM. The uses of the proposed optical waveguide LWL and the sensor head SK are not limited to this, however. The document presented here proposes an optical waveguide LWL with the sensor element NV for such and other applications with similar measuring tasks. The sensor element NV has a carrier material TM in which a large number of diamonds DM are embedded. One or more or all of the diamonds DM of these diamonds DM have 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 fluorescent radiation FL when irradiated with pump radiation LB. The special feature of the optical waveguide 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 is essentially transparent after curing for radiation with a pump radiation wavelength λ _pmp of the pump radiation LB with which the NV centers NVZ and/or the other paramagnetic centers are pumped. Essentially means that the losses that undoubtedly occur are still so low that the functionality of the device for the application in question is still ensured. Likewise, the carrier material TM should be essentially transparent for radiation with a fluorescence wavelength λ _fl of the fluorescence radiation LB of the NV centers NVZ or paramagnetic centers. Essentially means that the losses that undoubtedly occur are still so low that the functionality of the device for the application in question is still ensured. By curing a previously liquid carrier medium TM, the production of such an optical waveguide LWL is particularly simple and process-reliable with a high C _pk value.

The document presented here 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 has a sensor element NV with a carrier TM. A large number of diamonds or nanodiamonds DM are preferably embedded in the carrier TM. The carrier material TM preferably comprises glass and/or a hardened plastic. The carrier material TM fixes the diamonds DM relative to the first end ELWL1 of the optical waveguide LWL and prevents repositioning of the diamonds DM. Preferably, the carrier material TM is transparent after solidification in the manufacturing process for radiation with the pump radiation wavelength λ _pmp of the pump radiation LB and for radiation with the fluorescence wavelength λ _fl of the fluorescence radiation FL of the NV centers NVZ or paramagnetic centers in the diamonds DM or nanodiamonds. One or several or all of the diamonds or nanodiamonds DM of these diamonds or nanodiamonds DM typically have NV centers NVZ. The magnetic flux density B in the stray field BSTR of the magnetic field 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. The magnetic flux density B typically causes a reduction in 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 via 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 in a wavelength range of 400 nm to 700 nm wavelength and/or better 450 nm to 650 nm and/or better 500 nm to 550 nm and/or better 515 nm to 540 nm. A wavelength of 532 nm is clearly preferred as the pump radiation wavelength λ _pmp . In the case of NV centers in diamond or in diamonds, a laser diode from Osram of the type PLT5 520B is suitable, for example, as a pump radiation source PL with 520 nm pump radiation wavelength λ _pmp . The NV centers NVZ of the sensor element NV typically emit when irradiated with pump radiation LB of the above described pump radiation wavelength λ _pmp a fluorescence radiation FL with a typical fluorescence wavelength λ _fl of approx. 637 nm at NV centers NVZ. Other wavelengths can be achieved by plasmonic coupling with metallic nanocrystals in the carrier 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 carrier material TM of the sensor element NV with metallic nanoparticles. The sensor head housing GH preferably has a second channel KN for the exit of fluorescence radiation FL of the sensor element NV to a photodetector PD. The proposed device also has 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 if possible no pump radiation LB falls on the photodetector PD. This sub-device in the form of a filter F1 or dichroic mirror preferably allows the passage of radiation with the fluorescence wavelength λ _fl of the fluorescence radiation FL - e.g. 637 nm at NV centers NVZ with a phonon sideband of 637 nm to 850 nm - in the direction of the photodetector PD, while it does not allow the radiation with the pump radiation wavelength λ _pmp of the pump radiation LB of the pump radiation source PL and thus the modulated pump radiation LB to pass or guides it in such a way that it does not hit 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 in order to obtain information about the values of magnetic material parameters of the material on the surface OF of a workpiece or to obtain information comprising this information. Preferably, the material of the workpiece in the vicinity of the surface OF comprises a ferromagnetic material FM.

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 supply lines, such as when measuring magnetic fields with Hall sensors. Furthermore, the sensor element NV is completely diamagnetic. A reaction of fields from the workpiece to the evaluation electronics of the sensor system via the sensor element NV and the sensor head SK and the optical fiber LWL is very unlikely due to the galvanic isolation. This means that the system can also be used in high-voltage systems with workpieces that have a very high electrical potential. It is also conceivable that the workpiece is 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 LWL, the mechanical casing MH, the carrier material TM and the material of the sensor head housing GH, temperatures of up to 700°C and down to absolute zero for the workpiece and the ferromagnetic material FM are conceivable. State-of-the-art systems do not show this

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.

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 use, for example, diamond powder with 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 amount of the magnetic flux density B, but not the 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 assistants or less precise mechanical devices, which only have to insert the sensor element NV with the optical fiber LWL into a channel KN provided for this purpose in the sensor head housing GH and fasten it there, for example by means of gluing or screwing. This drastically reduces the manufacturing costs for such a sensor head SK. In order to achieve spatial isotropy, it is therefore advantageous if the orientation of the diamonds or nanodiamonds DM is stochastically distributed essentially evenly in the sensor element NV.

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

In order to minimize the number of optical fibers LWL and to keep the modifications to the sensor head SK to a minimum, it is advantageous to use a single optical fiber LWL for supplying the pump radiation LB from the pump radiation source PL to the sensor element NV and for returning the fluorescence resence radiation FL from the sensor element NV to the photodetector PD. In this case, only a single channel KN is necessary for mounting the optical waveguide LWL in the sensor head housing GH, so that the first channel KN is identical to the second channel KN e. The following text then refers to such a channel KN as a common channel KN.

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 carrier material TM and a first optical waveguide LWL to which the sensor element NV is attached, wherein the optical waveguide 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 waveguide LWL detects and transports back towards the photodetector PD.

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.

If the return of the fluorescence radiation FL from the sensor element NV to the photodetector PD is to take place 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 the fluorescence radiation FL of the sensor element NV and transports the fluorescence radiation FL in the direction of the photodetector PD.

As stated above, however, the first optical fiber LWL is preferably identical to the second optical fiber LWL. The document presented here refers to such an optical fiber LWL as a common optical fiber LWL. Such a common optical fiber LWL saves calibration effort and reduces assembly complexity and saves material and is therefore advantageous. In particular, the necessary modifications to the sensor head SK itself are reduced.

The first optical waveguide LWL has a first end ELWL1 and a second end ELWL2. The second optical waveguide LWL also has a first end ELWL1 and a second end ELWL2. The common optical waveguide LWL also has a first end ELWL1 and a second end ELWL2. The document presented here now proposes attaching the sensor element NV to the first end ELWL1 of the first optical waveguide LWL and/or second optical waveguide LWL or the common optical waveguide LWL in order to stabilize the optical coupling between the optical waveguide LWL and the sensor element NV.

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

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

The center line ML, which is an imaginary auxiliary construction to clarify the situation, penetrates the end surface EF at a center point MP of the end surface EF. The thickness d _l of the carrier material TM is preferably thicker at this center point MP than the thickness d _r at other points of the end surface EF of the first end of the first and/or the second or the common optical waveguide LWL. This has the advantage that light is reflected back into the optical waveguide LWL through the interface between the carrier material TM and air, and that the efficiency and effectiveness then increase.

Preferably, the carrier material TM therefore forms a lens LWLL at the first end ELWL1 of the optical waveguide LWL. The diameter D _LWLL of the lens LWLL is typically smaller than the diameter D _LWL of the optical waveguide LWL. The diameter D _LWLL of the lens LWLL can also be as large as the diameter D _LWL of the optical waveguide LWL, but this is not optimal based on experience in preparing the technical teaching of this document.

Preferably, the first optical fiber LWL in the area of the sensor head SK and/or within the sensor head SK is completely or partially covered by a mechanical sheath MH. Preferably, the second optical fiber LWL in the area of the sensor head SK and/or within the sensor head SK is also completely or partially covered by a mechanical sheath MH. Preferably, the common optical fiber LWL in the area of the sensor head SK and/or within the sensor head SK is completely or partially covered in the same way by a mechanical sheath MH. The mechanical sheath MH supports and protects the respective optical fiber LWL against the harsh conditions of the respective measuring situation. The mechanical sheath MH within the sensor head SK must meet the respective special requirements with regard to thermal and chemical stability against heat and operating fluids. The mechanical sheath MH is therefore preferably made of glass fabric or ceramic or plastic or the like.

The mechanical casing MH therefore preferably comprises a ceramic material or another non-magnetizable and/or electrically non-conductive material and/or a material that is stable at temperatures above 100°C and/or a material that is stable at temperatures above 140°C and/or a material that is stable at temperatures above 170°C and/or a material that is stable at temperatures above 200°C and/or a material that is stable at temperatures above 250°C, or comprises these or, in extreme cases, consists of these. 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 that is stable at temperatures above 100°C and/or a material that is stable at temperatures above 140°C and/or a material that is stable at temperatures above 170°C and/or a material that is stable at temperatures above 200°C and/or a material that is stable at temperatures above 250°C.

Preferably, the mechanical sheath MH is at least partially a tube or a small tube or a capillary or a cannula or a hose into which the respective optical waveguide LWL is pushed. This simplifies the manufacture of the system comprising optical waveguide LWL, sensor element NV and mechanical sheath MH. The inner diameter D _ro 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 waveguide lens LWLL and the diameter DLWL of the optical waveguide LWL.

In order to minimize the access of extraneous light to the sensor element NV during operation, it is useful if the first gap between the edge of the first channel KN and the first optical fiber LWL is completely, partially or in sections closed with an optically opaque filling compound. For the same reason, it is useful if the second gap between the edge of the second channel KN and the second optical fiber LWL is completely, partially or in sections closed with an optically opaque filling compound and/or if the common gap between the edge of the common channel KN and the common optical fiber LWL is completely, partially or in sections closed with an optically essentially opaque filling compound. The common filling compound can secure the respective optical fiber LWL in the respective channel KN of the sensor head housing GH.

Preferably, the device is designed to determine the temporal value profile of the intensity of the fluorescent radiation FL, in particular in the form of a receiver output signal S0. Furthermore, the device is preferably designed to determine the temporal value profile of the amplitude value of the temporal value profile of the intensity of the fluorescent radiation FL from the temporal value profile of the intensity of the fluorescent radiation FL, in particular from the receiver output signal S0 and in particular by means of a lock-in amplifier LIV or a functionally equivalent sub-device.

The document presented here proposes an optical waveguide LWL with a sensor element NV for such and other applications with similar measuring tasks. The sensor element NV has a carrier material TM in which a large number of diamonds or nanodiamonds DM are embedded. One or more or all diamonds or nanodiamonds DM of these diamonds DM have 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 a fluorescent radiation FL. The special feature of the optical waveguide 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 is essentially transparent after curing for radiation with a pump radiation wavelength λ _pmp of the pump radiation LB with which the NV centers NVZ and/or the other paramagnetic centers are pumped. Essentially means that the losses that undoubtedly occur are still so low that the functionality of the application in question is still ensured. Likewise, the carrier material TM should be essentially transparent for radiation with a fluorescence wavelength λ _fl of the fluorescence radiation LB of the NV centers or the paramagnetic centers. Essentially means that the losses that undoubtedly occur are still so low that the functionality of the application in question is still ensured. By curing a previously liquid carrier medium TM, the production of such an optical waveguide LWL is particularly simple and process-reliable with a high C _pk value.

In one variant of the optical waveguide, the diamonds or nanodiamonds DM in the carrier material TM are essentially oriented differently from one another, each with a substantially different orientation. This has the advantage that the sensor element behaves isotropically and does not show a preferred direction. The mixture of various diamond crystals homogenizes the measurement results and improves the C _pk value.

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

Preferably, the optical waveguide LWL is designed or intended to transport pump radiation LB from the pump radiation source PL to the sensor element NV, so that the pump radiation LB irradiates the sensor element NV with radiation of the pump radiation wavelength λ _pmp .

The optical waveguide LWL is preferably also designed or intended to detect fluorescent radiation FL of the sensor element NV and to transport the fluorescent radiation FL in the direction of a photodetector PD.

The proposed optical waveguide LWL again 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 waveguide LWL.

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

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

The imaginary virtual center line ML of the optical waveguide LWL penetrates the end face EF of the optical waveguide LWL at the first end ELWL1 of the optical waveguide LWL at a center point MP of the end face EF of the optical waveguide LWL. Preferably, the thickness d _l of the carrier material TM at this center point MP is thicker than the thickness d _r at other points of the end face EF of the first end ELWL1 of the optical waveguide LWL. This forms an optical functional element at the first end ELWL1 of the optical waveguide LWL. This improves the coupling of electromagnetic radiation from the core LWLC of the optical waveguide LWL into the sensor element NV and vice versa.

Preferably, the carrier material TM therefore forms a lens LWLL at the first end ELWL1 of the optical waveguide LWL, the diameter D _LWLL of which is preferably smaller than the diameter D _LWL of the optical waveguide LWL or as large as the diameter D _LWL of the optical waveguide LWL. This reduces the measuring volume of the sensor element and thus increases the spatial resolution of magnetic measurements. The method presented here can therefore then detect particularly small cracks RI in the surface OF of the material of the workpiece using the proposed device.

Preferably, the first optical waveguide LWL is completely or partially covered by a first mechanical casing MH. Preferably, the mechanical casing MH 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 has such a material. This protects the sensor element NV and the light waves conductor LWL from damage. The mechanical sheath MH is preferably made of a ceramic material or of another non-magnetizable and/or electrically non-conductive material and/or of a material that is stable at temperatures above 100°C and/or of a material that is stable at temperatures above 140°C and/or of a material that is stable at temperatures above 170°C and/or of a material that is stable at temperatures above 200°C and/or of a material that is stable at temperatures above 250°C.

For better processing and assembly, the mechanical sheath MH preferably comprises at least in sections a tube or pipe or a capillary or a cannula or a hose, in particular a fabric hose.

The fluorescence radiation of the NV centers NVZ and/or the other paramagnetic centers in the diamonds or the nanodiamonds DM of the carrier material TM and in particular the fluorescence wavelength λ _fl of their fluorescence radiation FL can be modified, for example, by means of plasmonic coupling by metallic nanoparticles that are also mixed into the carrier material TM. In this case, the carrier material TM can then, for example, have metallic nanoparticles with a diameter of less than 200 nm and/or less than 100 nm and/or less than 50 nm and/or less than 20 nm and/or less than 10 nm and/or less than 5 nm, which are then later embedded in the solidified carrier material TM. This improves the applicability in special applications.

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

These metallic nanoparticles typically comprise 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. The former are particularly preferred.

The atoms of the metal of the nanoparticles comprise one or more elements of the periodic table. Each of these elements occurs in different isotopes in nature with a respective natural isotope mixing ratio. Each isotope of an element has a natural proportion corresponding to the natural isotope mixing ratio of this element. With regard to these proportions and the values, the document presented here refers to the German patent application EN 10 2020 125 178 A1 of the applicant. These isotopes each have a nuclear magnetic moment µ or not, depending on the isotope. Preferably, the metallic nanoparticles have an increased proportion in the isotope mixing ratio for at least one element that the metallic nanoparticles have compared to the natural proportion of the isotope mixing ratio for at least one of the following isotopes: ¹² C, ¹⁴ C, ²⁸ Si, ³⁰ Si, ⁷⁰ Ge, ⁷² Ge, ⁷⁴ Ge, ⁷⁶ Ge, ¹¹² Zn, ¹¹⁴ Zn, ¹¹⁶ Zn, ¹¹⁸ Zn, ¹²⁰ Zn, ¹²² Zn, ¹²⁴ Zn ¹⁶ O, ¹⁸ O, ³² S, ³⁴ S, ³⁶ S, ⁷⁴ Se, ⁷⁶ Se, ⁷⁸ Se, ⁸⁰ Se, ⁸² Se, ¹²⁰ Te, ¹²² Te, ¹²⁴ Te, 126 Te, ¹²⁸ Te, ^{130 Te, 24 Mg} , ²⁶ Mg, ⁴⁰ Ca, ⁴² Ca, ⁴⁴ Ca, ⁴⁶ Ca, ⁴⁸ Ca, ⁸⁴ Sr, ⁸⁶ Sr, ⁸⁸ Sr, ¹³⁰ Ba, ¹³² Ba, ¹³⁴ Ba, ¹³⁶ Ba, ¹³⁸ Ba, ⁴⁶ Ti, ⁴⁸ Ti, ⁵⁰ Ti, 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 W, ¹⁸² W, ¹⁸⁴ W, ¹⁸⁶ W, ⁵⁴ Fe, ⁵⁶ Fe, ⁵⁸ Fe, ⁹⁶ Ru, ⁹⁸ Ru, ¹⁰⁰ Ru, ¹⁰² Ru, ¹⁰⁴ Ru, ¹⁸⁴ Os, ¹⁸⁶ Os, ¹⁸⁸ Os, ¹⁹⁰ Os, ¹⁹² Os ⁵⁸ Ni, ⁶⁰ Ni, ⁶² Ni, ⁶⁴ Ni, ¹⁰² Pd, ¹⁰² Pd, ¹⁰⁴ Pd, ¹⁰⁶ Pd, ¹⁰⁸ Pd, ¹¹⁰ Pd, ¹⁹⁰ Pt, ¹⁹² Pt, ¹⁹⁴ Pt, ¹⁹⁶ Pt, ¹⁹⁸ Pt ⁶⁴ Zn, ⁶⁶ Zn, ⁶⁸ Zn, ⁷⁰ Zn, ¹⁰⁶ Cd, ¹⁰⁸ Cd, ¹¹⁰ Cd, ¹¹² Cd, ¹¹⁴ Cd, ¹¹⁶ Cd, ¹⁹⁶ Hg, ¹⁹⁸ Hg, ²⁰⁰ Hg, ²⁰² Hg, ²⁰⁴ Hg ¹³⁶ Ce, ¹³⁸ Ce, ¹⁴⁰ Ce, ¹⁴² Ce, ¹⁴² Nd, ¹⁴⁴ Nd, ¹⁴⁶ Nd, ¹⁴⁸ Nd, ¹⁵⁰ Nd, ¹⁴⁴ Sm, 146 Sm, ¹⁴⁸ Sm, ¹⁵⁰ Sm, ¹⁵² Sm, ¹⁵⁴ Sm, ¹⁵² Gd, ¹⁵⁴ Gd, ¹⁵⁶ Gd, ¹⁵⁸ Gd, ¹⁶⁰ Gd, ¹⁵⁶ Dy, ¹⁵⁸ Dy, ^{160 Dy, 162 Dy, 164 Dy , 162} Er, ¹⁶⁴ Er, ¹⁶⁶ Er, ¹⁶⁸ Er, ¹⁷⁰ Er, ¹⁶⁸ Yb, ¹⁷⁰ Yb, ¹⁷² Yb, ¹⁷⁴ Yb, ¹⁷⁶ Yb, ²³² Th, ²³⁴ Pa, ²³⁴ U, ²³⁸ U, ^{244 Pu} .

The optical waveguide LWL typically has an optical waveguide core LWLC. In the carrier material TM, the carrier material TM preferably forms an optical functional element at the first end ELWL1 of the optical waveguide LWL. This in turn improves the optical coupling between the optical waveguide LWL and the carrier material TM. The optical functional element then interacts optically with the optical waveguide core LWLC of the optical waveguide LWL at the first end ELWL1 of the optical waveguide LWL.

The optical functional element preferably has an optical waveguide lens LWLL, in particular in the form of a thickening of the carrier material TM in the region of the optical functional element.

• • Bereitstellen 140 eines Lichtwellenleiters LWL, wobei der Lichtwellenleiter LWL ein erstes Ende ELWL1 und ein zweites Ende ELWL2 aufweist;
• • Bereitstellen 142 eines flüssigen und mittels elektromagnetischer Strahlung einer Aushärtewellenlänge λ_H härtbaren Trägermaterials TM, wobei in das Trägermaterial TM eine Vielzahl von Diamanten DM, vorzugsweise Nanodiamanten, eingebettet sind und wobei einer oder mehrere oder alle Diamanten DM dieser Diamanten DM NV-Zentren NVZ und/oder andere paramagnetischen Zentren aufweisen und wobei die NV-Zentren NVZ der Diamanten DM des Trägermaterials TM und/oder die anderen paramagnetischen Zentren der Diamanten DM des Trägermaterials TM bei Bestrahlung mit Pumpstrahlung LB zumindest eine Fluoreszenzstrahlung FL emittieren;
• • Benetzen 145 des ersten Endes des Lichtwellenleiters TM auf eine Benetzungslänge L_B mit dem Trägermaterial TM, das die Vielzahl eingebetteter Diamanten DM aufweist;
• • Einspeisen 150 elektromagnetischer Strahlung in das zweite Ende des Lichtwellenleiters LWL, wobei die Wellenlänge dieser elektromagnetischen Strahlung, die Aushärtewellenlänge λ_H, so gewählt ist, dass das Trägermaterial TM am zweiten Ende des Lichtwellenleiters LWL aushärtet und sich in einen Festkörper wandelt.
• • Entfernen 160 des nicht ausgehärteten Trägermaterials TM insbesondere mittels eines Lösungsmittels, wobei der verbleibende Film des Trägermaterials TM am ersten Ende des Lichtwellenleiters LWL das Sensorelement NV bildet.

The essence of the document presented here is that it also describes a method for producing an optical waveguide LWL as previously described and used, and The proposed procedure includes the following steps:

• • Providing 140 an optical waveguide LWL, wherein the optical waveguide LWL has a first end ELWL1 and a second end ELWL2;
• • Providing 142 a liquid carrier material TM which can be hardened by means of electromagnetic radiation of a curing wavelength λ _H , wherein a plurality of diamonds DM, preferably nanodiamonds, are embedded in the carrier material TM and wherein one or several or all diamonds DM 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 carrier material TM and/or the other paramagnetic centers of the diamonds DM of the carrier material TM emit at least one fluorescence radiation FL when irradiated with pump radiation LB;
• • Wetting 145 the first end of the optical waveguide TM to a wetting length L _B with the carrier material TM having the plurality of embedded diamonds DM;
• • Feeding 150 electromagnetic radiation into the second end of the optical waveguide LWL, wherein the wavelength of this electromagnetic radiation, the curing wavelength λ _H , is selected such that the carrier material TM cures at the second end of the optical waveguide LWL and turns into a solid.
• • 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 of the optical waveguide LWL forms the sensor element NV.

Typically, the carrier material TM only partially cures, which enables the formation of the optical functional element.

The electromagnetic radiation with the curing wavelength λ _H has a penetration depth into the carrier material TM, so that the carrier material TM only cures up to a thickness d _l of the carrier material and thus forms the optical functional element, which was only recognized as a surprising and advantageous procedure in the context of the elaboration of the technical teaching of this document.

The radiation fed into the second end ELWL2 of the optical waveguide LWL for curing is preferably UV radiation. Radiation for curing with a curing wavelength λ _H between 320-380 nm is particularly preferred.

In certain applications, nanoparticles with a diameter of less than 200 nm and/or less than 100 nm and/or less than 50 nm and/or less than 20 nm and/or less than 10 nm and/or less than 5 nm can be mixed into the carrier material TM before it is provided, so that they are embedded in the carrier material TM after curing. These are preferably metallic nanoparticles.

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

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.

The atoms of the metal in the nanoparticles naturally comprise one or more elements of the periodic table of elements. Each of these elements occurs in nature in various isotopes with a respective natural isotope mixing ratio. Each isotope in nature has a natural proportion corresponding to the natural isotope mixing ratio. These isotopes may or may not have a nuclear magnetic moment µ, depending on the isotope. The metallic nanoparticles have, for at least one element that the metallic nanoparticles have, an increased proportion in the isotope mixing ratio compared to the natural proportion of the isotope mixing ratio for at least one of the following isotopes: ¹² C, ¹⁴ C, ²⁸ Si, ³⁰ Si, ⁷⁰ Ge, ⁷² Ge, ⁷⁴ Ge, ⁷⁶ Ge, ¹¹² Zn, ¹¹⁴ Zn, ¹¹⁶ Zn, ¹¹⁸ Zn, ¹²⁰ Zn, ¹²² Zn, ¹²⁴ Zn ¹⁶ O, ¹⁸ O, ³² S, ³⁴ S, ³⁶ S, ⁷⁴ Se, ⁷⁶ Se, ⁷⁸ Se, ⁸⁰ Se, ⁸² Se, ¹²⁰ Te, ¹²² Te, ^{124 Te, 126 Te} , ¹²⁸ Te, ¹³⁰ Te, ²⁴ Mg, ²⁶ Mg, ⁴⁰ Ca, ⁴² Ca, ⁴⁴ Ca, ⁴⁶ Ca, ⁴⁸ Ca, ⁸⁴ Sr, ⁸⁶ Sr, ⁸⁸ Sr, ¹³⁰ Ba, ¹³² Ba, ¹³⁴ Ba, ¹³⁶ Ba, ¹³⁸ Ba, ⁴⁶ Ti, ⁴⁸ Ti, ⁵⁰ Ti, 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 W, ¹⁸² W, ¹⁸⁴ W, ¹⁸⁶ W, ⁵⁴ Fe, ⁵⁶ Fe, ⁵⁸ Fe, ⁹⁶ Ru, ⁹⁸ Ru, ¹⁰⁰ Ru, ¹⁰² Ru, ¹⁰⁴ Ru, ¹⁸⁴ Os, ¹⁸⁶ Os, ¹⁸⁸ Os, ¹⁹⁰ Os, ¹⁹² Os ⁵⁸ Ni, ⁶⁰ Ni, ⁶² Ni, ¹⁰² Pd, ¹⁰² Pd, ¹⁰⁴ Pd ^{, 106 Pd, 108 Pd, 110 Pd, 190 Pt, 192 Pt, 194 Pt, 196 Pt, 198 Pt 64 Zn , 66 Zn , 68 Zn , 70 Zn} , ¹⁰⁶ Cd, ¹⁰⁸ Cd, ¹¹⁰ Cd, ¹¹² Cd, ¹¹⁴ Cd, ¹¹⁶ Cd, ¹⁹⁶ Hg, ¹⁹⁸ Hg, ²⁰⁰ Hg, ²⁰² Hg, ²⁰⁴ Hg ¹³⁶ Ce, ¹³⁸ Ce, ¹⁴⁰ Ce, ¹⁴² Ce, ¹⁴² Nd, ¹⁴⁴ Nd, ¹⁴⁶ Nd, ¹⁴⁸ Nd, ¹⁵⁰ Nd, ¹⁴⁴ Sm, ¹⁴⁶ Sm, ¹⁴⁸ Sm, ¹⁵⁰ Sm, ¹⁵² Sm, ¹⁵⁴ Sm, 152 Gd, ¹⁵⁴ Gd, ¹⁵⁶ Gd, ¹⁵⁸ Gd, ¹⁶⁰ Gd, ¹⁵⁶ Dy, ¹⁵⁸ Dy, ¹⁶⁰ Dy, ¹⁶² Dy, ¹⁶⁴ Dy, ¹⁶² Er, ¹⁶⁴ Er, ¹⁶⁶ Er, ¹⁶⁸ Er, ¹⁷⁰ Er, 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 mixing ratio of the above isotopes is increased by 50% or more.

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

The optical functional element LWL thus formed can then optically interact with the optical waveguide core LWLC at the first end ELWL1 of the optical waveguide LWL when optical radiation, in particular pump radiation LB with the pump radiation wavelength λ _pmp , is fed into the second end ELWL2 of the optical waveguide LWL.

The optical functional element then has an optical waveguide lens LWLL, in particular in the form of a thickening of the carrier material TM.

The document presented here suggests, 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 the document presented here.

Norland Optical Adhesive 61 (“NOA 61”) is a clear, colorless liquid photopolymer that cures under ultraviolet light. Because it is a one-component, 100% solids system, it offers many advantages in bonding applications where the adhesive can be exposed to UV light. Using NOA 61 eliminates the need for premixing, drying, or heat curing common with other adhesive systems. Cure time is short and depends on the thickness applied and the UV light energy available. It is particularly useful when the TM carrier meets Federal Specification MIL-A-3920 for optical adhesives. NOA 61 meets Federal Specification MIL-A-3920 for optical adhesives. The TM carrier is designed to provide the best possible optical bond to glass surfaces, metals, fiberglass, and glass-filled plastics. NOA61 meets this requirement. It is particularly advantageous to use a carrier material TM, which 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.

The TM substrate material is also said to have excellent clarity, low shrinkage and light flexibility. These properties are important to enable the user to produce high-quality NV sensor elements and achieve long-term performance under changing aggressive environmental conditions.

NOA 61 cures with ultraviolet light as desired for the substrate TM, with maximum absorption in the range of 320-380 nanometers for the curing wavelength λ _H and highest sensitivity achieved at 365 nm. The recommended energy for complete cure is 3 Joules/cm ² at these wavelengths. Curing is not inhibited by oxygen, so all areas in contact with air will cure to a non-tacky state when exposed to ultraviolet light.

For most optical applications, curing is a two-step process. First, there is a short, uniform exposure to light, called pre-cure. The cure time is long enough to solidify the bond and allow it to be moved without disturbing the alignment. This is followed by a longer cure under UV light to achieve complete cross-linking and solvent resistance of the adhesive. Cure can be achieved in 10 seconds with a 100 watt mercury lamp at 6". If a longer time is required for alignment, it can be extended to several minutes using a very low intensity light source. Final cure can be achieved in 5 to 10 minutes with the 100 watt mercury lamp.

Pre-curing allows the user to quickly align and fix the fiber optic cable when needed and minimizes the number of fixtures required. After pre-fixing, excess adhesive can be wiped off with a cloth moistened with alcohol or acetone as an example solvent. The fiber optic cable should be inspected at this time and scrap should be placed in methylene chloride. The coated area of the sensor elements NV must be soaked in the solvent and will normally dissolve overnight. The time required to dissolve the carrier material TM depends on the extent of curing and the size of the coating.

After curing, NOA 61 has very good adhesion and solvent resistance, but it has not yet reached its optimum adhesion to glass. This is achieved by ageing for a period of about 1 week, during which a chemical bond is formed between the glass and the adhesive. This optimum adhesion can also be achieved by ageing at 50° C for 12 hours in a temperature cabinet.

Before aging, NOA 61 can withstand temperatures from -15°C to 60°C when used to coat the optical fiber LWL. After aging, it can withstand temperatures from -150°C to 125°C. As a coating on the surface of the optical fiber, NOA 61 can withstand 260°C for three hours and reflow soldering. This means that the NV sensor element can be used to measure the magnetic flux density B up to these temperatures. The document presented here therefore proposes the use of a proposed optical waveguide LWL 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.

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

Typical properties of NOA 61 as an exemplary vehicle are a solids content of 100%, a viscosity at 25°C of 300 cps, a refractive index of the cured polymer of 1.56, an elongation at break of 38%, a modulus of elasticity (psi) of 150,000, a tensile strength (psi) of 3,000 and a hardness of Shore D 85.

Advantage

• • Sensor ist galvanisch getrennt
• • Diamagnetischer Messkopf (Sensor beeinflusst Messung nicht)
• • Unanfällig gegenüber elektrostatischen Störungen
• • Kleines Messvolumen (Fibercore- Durchmesser 9µm) bis 1000µm), Dicke des Materials an der Spitze variabel
• • Messfrequenz DC bis zu MHz Bereich
• • Gleicher Sensor für DC / AC Magnetfeldanregung

But the advantages are not limited to this.

• • Sensor is galvanically isolated
• • Diamagnetic measuring head (sensor does not affect measurement)
• • Not susceptible to electrostatic interference
• • Small measuring volume (fiber core diameter 9µm) to 1000µm), thickness of the material at the tip variable
• • Measuring frequency DC up to MHz range
• • Same sensor for DC / AC magnetic field excitation

Features of the proposal

The list of features only 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 the document presented here.

Feature 1: Sensor head SK,
with a sensor element NV,
wherein the sensor element NV comprises a plurality 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 support surface AF and
wherein the optical waveguide LWL with the sensor element NV is installed in the sensor head housing GH at an angle α to the support surface AF of the sensor head SK between 10° and 70° and
wherein the sensor element NV is located at a distance from the support 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 waveguide LWL exits the sensor head housing GH at an angle β to the perpendicular AFS to the support surface AF of the sensor head SK support surface AF of 45° to 135° and/or from 70° to 110° and/or from 80° to 100° and/or from 85° to 95° and/or from 87° to 93°.

Feature 2: Sensor head SK,
with a sensor element NV,
wherein the sensor element NV comprises a plurality 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 electric 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 support surface AF and
wherein the optical waveguide LWL with the sensor element NV is installed in the sensor head housing GH and
wherein the sensor element NV is located at a distance from the support surface AF which is smaller than the diameter D _LWLMH of the coated optical waveguide LWL and
wherein 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 are 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 electric coil are device parts 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 flows through 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 material of the workpiece 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 with a second axis.

Feature 6: Sensor head SK according to feature 5,
wherein the second axis of the ferromagnetic support ST is substantially 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 waveguide 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 of 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 an optical fiber lens LWLL and
wherein the optical waveguide lens LWLL comprises a plurality of diamonds DM and/or nanodiamonds with NV centers NVZ and/or paramagnetic centers and
wherein the optical waveguide lens LWLL is located at a first end ELWL1 of the optical waveguide LWL and
wherein the optical waveguide lens LWLL has a diameter D _LWLL of the optical waveguide lens LWLL which is smaller than the diameter D _LWL of the optical waveguide LWL.

Feature 12: Sensor head SK,
with a sensor element NV,
wherein the sensor element NV comprises a plurality 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 an optical fiber lens LWLL and
wherein the optical waveguide lens LWLL comprises a plurality of diamonds DM and/or nanodiamonds with NV centers NVZ and/or paramagnetic centers and
wherein the optical waveguide lens LWLL is located at a first end ELWL1 of the optical waveguide LWL and
wherein the optical waveguide lens LWLL has a diameter D _LWLL of the optical waveguide lens LWLL which is smaller than the diameter D _LWL of the optical waveguide LWL.

Feature 13: Sensor head SK according to feature 12,
wherein the permanent magnet PM and/or the electric 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 support surface AF and
wherein the optical waveguide LWL with the sensor element NV is installed in the sensor head housing GH and
wherein the sensor element NV is located at a distance from the support surface AF which is smaller than the diameter D _LWLMH of the coated optical waveguide LWL and
wherein 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 are 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 electric coil are device parts 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 flows through 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 material of the workpiece 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 with a second axis.

Feature 18: Sensor head SK according to feature 17,
wherein the second axis of the ferromagnetic support ST is substantially 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 waveguide 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 of 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.

• Bereitstellen 140 eines Lichtwellenleiters LWL,
  • - wobei der Lichtwellenleiter LWL ein erstes Ende ELWL1 und ein zweites Ende ELWL2 aufweist;
• Bereitstellen 145 eines flüssigen und mittels elektromagnetischer Strahlung einer Aushärtewellenlänge λ_H härtbaren Trägermaterials TM,
  • - wobei das Trägermaterial TM eine Vielzahl von Diamanten DM aufweist und
  • - wobei einer oder mehrere oder alle Diamanten DM dieser Diamanten DM NV-Zentren NVZ und/oder andere paramagnetischen Zentren aufweisen und
  • - wobei die NV-Zentren NVZ der Diamanten DM des Trägermaterials TM und/oder die anderen paramagnetischen Zentren der Diamanten DM des Trägermaterials TM bei Bestrahlung mit Pumpstrahlung LB zumindest eine Fluoreszenzstrahlung FL emittieren;
• Benetzen 150 des ersten Endes ELWL1 des Lichtwellenleiters TM auf eine Benetzungslänge L_B mit dem Trägermaterial TM;
• Einspeisen 155 elektromagnetischer Strahlung in das zweite Ende ELWL2 des Lichtwellenleiters LWL,
  • - wobei die Wellenlänge dieser elektromagnetischen Strahlung, der Aushärtewellenlänge λ_H entspricht,
  • - sodass das Trägermaterial TM am zweiten Ende ELWL2 des Lichtwellenleiters LWL aushärtet und
  • - sodass das Trägermaterial TM am zweiten Ende ELWL2 des Lichtwellenleiters LWL sich in einen Festkörper wandelt und
  • - wobei das ausgehärtete Trägermaterial TM dann somit das Sensorelement NV ausbildet und
  • - wobei dann das Sensorelement NV Diamanten DM mit NV-Zentren NVZ der Diamanten DM und/oder mit anderen paramagnetischen Zentren der Diamanten DM umfasst, die bei Bestrahlung mit Pumpstrahlung LB zumindest eine Fluoreszenzstrahlung FL emittieren;
• Entfernen 160 des nicht ausgehärteten Trägermaterials TM, insbesondere mittels eines Lösungsmittels, wobei der verbleibende Film des Trägermaterials TM am ersten Ende ELWL1 des Lichtwellenleiters LWL das Sensorelement NV bildet;
• Bereitstellen 165 eines Sensorkopfgehäuses GH des Sensorkopfes SK mit einem Kanal KN und einer Erregungsquelle für eine magnetische Erregung H, insbesondere eines Permanentmagneten PM;
• Einbau 170 des Lichtwellenleiters LWL mit dem neu gebildeten Sensorelement NV in den Kanal KN des Sensorkopfgehäuses GH des Sensorkopfes SK und Einbau der Erregungsquelle für eine magnetische Erregung H in das Sensorkopfgehäuses GH des Sensorkopfes SK;
• Verwendung 180 des Sensorkopfes SK zur ortsaufgelösten Vermessung der magnetischen Eigenschaften des Materials eines Werkstücks in der Nähe der Oberfläche OF des Werkstücks,
• wobei der Abstand zwischen dem Mittelpunkt MP der Endfläche EF des ersten Endes ELWL1 des Lichtwellenleiters LWL und der Oberfläche OF des Werkstücks
  • - kleiner als der fünffache Durchmesser D_LWLMH des ummantelten Lichtwellenleiters LWL und/oder
  • - kleiner als der doppelte Durchmesser D_LWLMH des ummantelten Lichtwellenleiters LWL und/oder
  • - kleiner als der Durchmesser D_LWLMH des ummantelten Lichtwellenleiters LWL und/oder
  • - kleiner als der halbe Durchmesser D_LWLMH des ummantelten Lichtwellenleiters LWL ist.

Feature 23: Method for producing a sensor head SK comprising the steps:

• Providing 140 an optical fiber LWL,
  • - wherein the optical waveguide LWL has a first end ELWL1 and a second end ELWL2;
• Providing 145 a liquid carrier material TM which can be cured by means of electromagnetic radiation having a curing wavelength λ _H ,
  • - wherein the carrier material TM comprises a plurality of diamonds DM and
  • - wherein one or more or all of the diamonds DM 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 carrier material TM and/or the other paramagnetic centers of the diamonds DM of the carrier material TM emit at least one fluorescence radiation FL when irradiated with pump radiation LB;
• Wetting 150 the first end ELWL1 of the optical waveguide 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 corresponds to the curing wavelength λ _H ,
  • - so that the carrier material TM hardens at the second end ELWL2 of the optical fiber LWL and
  • - so that the carrier material TM at the second end ELWL2 of the optical waveguide LWL turns into a solid body and
  • - whereby the cured 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 emit at least one fluorescence radiation FL when irradiated with pump radiation LB;
• Removing 160 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 waveguide 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 a magnetic excitation H, in particular a permanent magnet PM;
• Installation 170 of the optical waveguide LWL with the newly formed sensor element NV in 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 in the sensor head housing GH of the sensor head SK;
• 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 MP of the end face EF of the first end ELWL1 of the optical fiber LWL and the surface OF of the workpiece
  • - less 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
  • - is smaller than half the diameter D _LWLMH of the coated optical fiber LWL.

Feature 24: Procedure according to feature 23
wherein 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 resolving 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 they are spaced apart from each other according to the resolution and
Such disturbances may include, for example, cracks, blowholes, 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 support 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 recording the values of a flux density measurement signal S4 which depends on the intensity of the fluorescence radiation FL from NV centers NVZ and/or paramagnetic centers in diamonds of a sensor element NV of the sensor head SK;
Infer that a fault has occurred 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 the displacement of the sensor head SK on the surface OF of the workpiece parallel to the surface OF of the workpiece along a path x and the simultaneous detection of the values of the flux density measurement signal S4 comprise a simultaneous detection and/or estimation of one or more coordinates of the location of the sensor head SK or an equivalent value at the time of detection of 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 respectively recorded coordinates on a screen and/or providing data for such a display.

Miscellaneous

The above description is not exhaustive and does not limit this disclosure to the examples shown. Other variations to the disclosed examples can be understood and practiced by those of ordinary skill in the art from the drawings, the disclosure and the claims. The indefinite articles "a" or "an" and their inflections do not exclude a plurality, while the mention of a certain number of elements does not exclude the possibility of more or fewer elements being present. A single unit may perform the functions of several elements mentioned in the disclosure, and conversely, several elements may perform the function of a unit. Numerous alternatives, equivalents, variations and combinations are possible without departing from the scope of the present disclosure.

Unless otherwise stated, all features of the present invention can be freely combined with one another. This applies to the entire document presented here. The features described in the description of the figures can also be freely combined with the other features as features of the invention, unless otherwise stated. A restriction of individual features of the exemplary embodiments to the combination with other features of the exemplary embodiments is expressly not intended. In addition, material features of the device can be reformulated and used as process features, and process features can be reformulated as material features of the device. Such a reformulation is therefore automatically disclosed.

In the foregoing detailed description, reference is made to the accompanying drawings. The examples in the description and drawings should be considered as illustrative and are not to be considered as limiting the specific example or element described. Multiple examples may be derived from the foregoing description and/or drawings and/or the claims by modifying, combining or varying certain elements. In addition, examples or elements not described verbatim may be derived from the description and/or drawings by a person skilled in the art.

List of characters

• 1 shows an exemplary and schematically simplified example of an exemplary, proposed material measuring system with a proposed sensor head SK.
• 2 shows an optical fiber LWL with a sensor element NV directly on the center MP of the core of the optical fiber LWL.
• 3 shows a cross-section through the exemplary first end ELWL1 of a proposed optical fiber LWL.
• 4 shows a sensor head SK with the mechanical sheath of the optical fiber LWL, which is covered by the mechanical sheath MH.
• 5 shows the sensor head SK of the 4 in supervision ( 5a) and in side view ( 5b) as a cross-section.
• 6 shows the steps of the method for producing a proposed sensor head SK and its use.
• 7a shows an exemplary workpiece made of a ferromagnetic material FM in plan view.
• 7b shows an example of the value curve of the obtained measurement signal S4 depending on the position x of the sensor head SK on the surface OF of the workpiece of the 7a shown.

Description of the characters

The figures illustrate the proposal schematically and in a simplified manner. The disclosure of the document presented here is not limited to the figures and also includes other combinations.

Figure 1

1 shows, by way of example and in a simplified schematic, 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 comprises a permanent magnet PM. The permanent magnet PM is preferably tubular. The permanent magnet PM preferably has a permanent magnet symmetry axis AX. The permanent magnet PM is preferably 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 distance d _pm from the support surface AF of the sensor head SK. Since the diameter of the optical fiber LWL is less than 1 mm, the permanent magnet distance d _pm is less than 1 mm, better less than 0.5 mm, better less than 200 µm, better less than 100 µm, better less than 20 µm. The permanent magnet distance d _pm is preferably slightly larger in the area of the sensor element NV than the diameter of the optical fiber LWL. The permanent magnet distance d _pm is preferably less than 200% larger than the diameter of the optical fiber LWL, better less than 100% larger than the diameter of the optical fiber LWL, better less than 50% larger than the diameter of the optical fiber LWL, better less than 25% larger than the diameter of the optical fiber LWL, better less than 10% larger than the diameter of the optical fiber LWL, better less than 5% larger than the diameter of the optical fiber LWL. The material of the housing GH of the sensor head SK is preferably non-magnetic and/or non-magnetizable. For the purposes of the document presented here, a material is considered non-magnetic if the magnetic permeability µ _τ of this material is µ _τ <1. The document presented here recommends the use of materials with the lowest possible magnetic permeability µ _τ as the material of the sensor head housing GH. The sensor element NV is preferably located on the extended axis of symmetry, the permanent magnet symmetry axis AX of the permanent magnet PM.

For the measurement, the operator or a mechanical actuator brings the sensor head SK with the support 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.

If the workpiece to be measured has a disturbance on its surface OF that influences the magnetic flux density B, the magnetic flux density B that flows 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 can be, for example, a crack Ri or a hole or a depression or another defect in the material of the workpiece near the surface OF of the workpiece.

The generator G generates the transmission pre-signal S5w. The transmission pre-signal S5w is preferably pulse-modulated with a pulse frequency. It is particularly preferably 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 transmission pre-signal in order to be able to use the pump radiation source PL. The resulting transmission signal S5 preferably has no negative signal components. The pump radiation source PL generates a modulated pump radiation LB depending on the transmission signal S5. In the example of the 1 the pump radiation source transmits the pump radiation LB through a dichroic mirror F1 and radiates pump radiation LB into the optical waveguide LWL. The sensor head housing GH has at least one channel KN through which the optical waveguide LWL is introduced into the sensor head housing GH. The sensor element NV is preferably located at the end of the optical waveguide LWL. The sensor element NV preferably comprises a large number of nanodiamonds or diamonds DM, which preferably have a statistically evenly distributed different crystal orientation and which are embedded in a matrix material. Typically, the matrix material made of a carrier material TM mechanically connects these nanodiamonds ND to the first end ELWL1 of the optical waveguide LWL. The actual optical waveguide LWL preferably has an optical waveguide diameter D _LWL of approx. 100 µm. Smaller optical waveguide diameters D _LWL are preferred. Larger optical waveguide diameters D _LWL are possible, however. In addition, the optical waveguide LWL typically has kink protection. The kink protection is preferably designed as a mechanical casing MH. The pump radiation LB of the pump radiation source PL hits the nanodiamonds or diamonds DM in the sensor element NV at the first end of the optical waveguide ELWL1. The sensor element NV preferably comprises diamonds with NV centers. Typically, the pump radiation LB excites the nanodiamonds or diamonds DM to emit a fluorescence radiation FL with a fluorescence wavelength µ _fl . Preferably, the sensor element NV is located at the first end ELWL1 of the optical waveguide LWL. Preferably, the sensor element has a diameter that is smaller than the diameter D _LWL of the optical waveguide LWL. Typically, the NV centers NVZ of the sensor element NV emit the fluorescence resonant radiation FL enters the optical waveguide LWL via the first end ELWL1 of the optical waveguide LWL. The fluorescence radiation FL exits the optical waveguide LWL at the other, second end ELWL2 of the optical waveguide LWL and irradiates, for example deflected by the dichroic mirror F1, preferably the photodetector PD. The dichroic mirror F1 deflects the scattered pump radiation LB in the example of the 1 not in the direction of the photodetector PD. As a result, the photodetector PD essentially only receives fluorescence radiation FL. Essentially, this means that the pump radiation LB and the other radiation that nevertheless hits the photodetector PD are essentially insignificant for the technical purpose of the device. To achieve this, the document presented here proposes the use of a light-tight housing for the light-sensitive device parts and the use of apertures to prevent the entry of unwanted radiation and unwanted effects due to scattered radiation. The photodetector PD preferably converts the intensity of the fluorescence radiation FL into a temporal value curve of a received signal S0. An exemplary amplifier V1 amplifies and, if necessary, filters the receiver output signal SO in the example of the 1 to the amplified receiver output signal S1. In the example of 1 an exemplary multiplier M1 multiplies the amplified receiver output signal S1 with the transmission pre-signal S5w to form the filter input signal S3. A low-pass filter TP typically removes the frequency components with the added frequencies of the transmission 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 form 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 transmission pre-signal S5w. This is a simple exemplary synchronous demodulator. The synchronous demodulator generates a signal S4 that symbolizes the correlation between the amplified receiver output signal S1 and the transmission 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 1 is that the optical waveguide LWL together with the sensor element NV and the other device parts of the sensor head SK typically do not comprise any ferromagnetic and/or electrically conductive materials and thus essentially do not influence the magnetic field of the workpiece, or the ferromagnetic material FM and the permanent magnet PM.

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 transmitted 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. The flux density measurement signal S4 is therefore a measure of the magnetic flux density B at the location of the NV centers NVZ in the sensor element NV.

In the example of 1 the sensor element NV is placed 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 pushes 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 only changes if this translational movement at the speed v influences the area of the ferromagnetic material that influences the magnetic stray field BSTR in terms of its distribution of physical parameters. Such an influence can cause an uneven distribution of physical parameters in the ferromagnetic material FM, which influences the magnetic stray field BSTR. The feed speed v of the sensor head SK relative to the workpiece with the ferromagnetic material FM is preferably constant. An operator preferably manually feeds the sensor head SK relative to the workpiece at the feed speed v. The document presented here proposes providing an actuator for production tests which places the sensor head SK with the support surface AF on the surface OF of the workpiece or 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 examined. Preferably, a computer system uses a coordinate sensor system to record the position of the sensor head SK and thus of the sensor element NV relative to the workpiece and thus the ferromagnetic material FM. Preferably, the computer system records the value of the flux density measurement signal S4 together with the coordinates of the position of the sensor head SK and thus the position of the sensor element NV. Preferably, the computer system stores these pairs of coordinates of the measuring point and measured value of the flux density measurement signal S4 in a memory of the computer system. The computer system can further process this data, for example, into a two- or three-dimensional model of the distribution of magnetizability. For example, the computer system can generate a two-dimensional Determine the distribution of the values of the flux density measurement 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, make it available as a JPEG image or functionally equivalent form. The feed rate v can be 0 m/s for a point measurement. A mechanical casing MH comprising ceramic or 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 using a screw SCHR. An external data bus EXTDB enables the half-bridge control CTR to communicate with a higher-level control system. The external data bus can be a wired or wireless data connection. Several parallel data connections, which can be implemented in different ways, are conceivable.

Figure 2

The 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 a part of the end surface EF of the optical fiber LWL, the sensor element NV is designed as an optical fiber lens LWLL.

Figure 3

3 shows a cross-section through the exemplary first end ELWL1 of a proposed optical waveguide LWL. The optical waveguide LWL has an optical waveguide core LWLC. The optical waveguide LWL can be a monomode optical waveguide or a multimode optical waveguide. The optical waveguide LWL can be a gradient optical waveguide or a step-index waveguide or the like, in which the optical waveguide core LWLC merges smoothly into the outer region of the optical waveguide LWL with regard to the refractive index. The mechanical sheath MH protects the optical waveguide LWL and preferably leaves the first end ELWL1 of the optical waveguide LWL free. The carrier material TM of the sensor element NV surrounds the first end ELWL1 of the optical waveguide LWL. The carrier material TM of the optical waveguide LWL is preferably transparent to the pump radiation wavelength λ _pmp and the fluorescence wavelength λ _fl . The transparency here refers to the dimensions of the optical waveguide LWL, which can have a diameter D _LWL that is certainly smaller than 100 µm. The end face EF of the optical waveguide LWL is preferably perpendicular to the optical axis of the optical waveguide LWL, which is drawn here as an example as the center line ML. At the point where the optical axis, i.e. the center line ML, passes through the end face EF, an optical waveguide lens LWLL is manufactured in the carrier material TM as a thickening of the carrier material TM. This is where the thickness d _l of the carrier material TM is typically the thickest. In the other areas of the sensor element NV, the optical waveguide LWL may only be thinly coated with the carrier material TM with a smaller thickness d _r . The thickness d _r can also be Dm. The diameter D _LWLL of the optical waveguide lens LWLL is typically smaller than the diameter D _LWL of the optical waveguide LWL. For clarity, the first end ELWL1 of the optical waveguide LWL with the end face EF and the optical waveguide lens LWLL is enlarged again on the left. The small, stochastically evenly distributed diamonds or nanodiamonds DM in the material of the carrier material TM are indicated for clarity. The diamonds DM nanodiamonds are preferably 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, smaller than 10 nm. Sizes over 100 nm are particularly preferred, since sizes smaller than 100 nm can cause special surface effects between the NV center NVZ and the diamond surface of the diamond DM in question. Preferably, a large number of these diamonds or nanodiamonds DM comprise one or more NV centers NVZ and/or one or more paramagnetic centers, which then generate the fluorescence radiation FL when irradiated with suitable pump radiation LB.

Figure 4

4 shows a sensor head SK with the mechanical cover of the optical fiber LWL, which is covered by the mechanical cover MH. The drawing shows the permanent magnet PM. The support surface AF is at the bottom and covered.

Figure 5

5 shows the sensor head of the 4 in supervision ( 5a) and in side view ( 5b) as a cross-section.

The mechanical casing 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 using a screw SCHR. It is conceivable to fix the mechanical casing 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 using an adhesive. The permanent magnet PM is designed as a cylinder, for example. The lower end of the permanent magnet PM has a distance d _pm to the support surface AF. The support surface AF is located in the example of the 5 on the surface OF of the exemplary ferromagnetic material FM of the workpiece. For example, there is a crack RI 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. The sensor element NV is preferably 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 area 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.

The example sensor head SK has the height d _SK1 . The example sensor head SK has the length d _SK2 . The example sensor head SK has the width d _SK3 .

On the top side opposite the support surface AF, the sensor head SK has a recess VT with the depth d _SK4 relative to the top side 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.

In the example of 5 the channel KN has a bend KI at an angle. Firstly, this has the positive effect of a certain mechanical clamping of the optical fiber LWL in the channel KN and secondly the effect that the optical fiber LWL can emerge from the sensor head SK parallel to the support surface AF. This has the advantage that the optical fiber LWL, due to its flexibility, comes to rest at a smaller distance from the sensor head SK, for example on a worktop, than without this bend KI. This reduces the torque that the optical fiber LWL exerts on the sensor head SK. Thirdly, this allows the sensor element NV to be positioned closer to the support surface AF of the sensor head SK. The optical fiber LWL therefore preferably forms an angle α with the support surface AF in the immediate vicinity of the sensor element NV, which angle is different from 90° and 0°. Typically, the angle α is between 15° and 65°, or better still 25° and 55°. Angles α of 30° and 45° are currently in use.

in the 5 a ferromagnetic support ST is provided, which directs the magnetic excitation H of the permanent magnet PM to the material of the workpiece, here the ferromagnetic material FM. In the example of the 5 The ferromagnetic support ST is an example of a ferromagnetic tube. The ferromagnetic support ST has in the example of the 5 example, approximately the same diameter as the permanent magnet PM. In the example of the 5 the ferromagnetic support ST has an opening OE in the lower area. The optical fiber LWL passes through this opening OE into the interior of the ferromagnetic support ST. This opening OE is therefore part of the channel KN in the sensor head housing GH. The ferromagnetic support ST is filled with a filling material of a core KE of the support ST and the permanent magnet PM. The channel KN continues 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 5 the rotational symmetry axis AX of the permanent magnet PM corresponds, for example, to the rotational symmetry axis of the ferromagnetic support ST. The channel KN in the core KE is therefore preferably designed in such a way that after the optical waveguide LWL has been introduced, the sensor element NV is located near the extension of this symmetry axis AX.

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, which is connected via at least one optical waveguide LWL. The optical waveguide LWL is equipped with a control and evaluation device (see 1 ) or is connected to it. The sensor head further comprises a sensor head housing GH made of a non-ferromagnetic material (µ _t <1). The sensor head SK preferably 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. The sensor head SK is preferably 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 via a support surface AF with an area of the surface OF of a workpiece when the sensor head SK is placed with the support surface AF on the surface OF of the workpiece.

Figure 6

• • Bereitstellen 140 eines Lichtwellenleiters LWL, wobei der Lichtwellenleiter LWL ein erstes Ende ELWL1 und ein zweites Ende ELWL2 aufweist;
• • Bereitstellen 145 eines flüssigen und mittels elektromagnetischer Strahlung einer Aushärtewellenlänge λ_H härtbaren Trägermaterials TM, wobei in das Trägermaterial (TM) eine Vielzahl von Diamanten DM bzw. Nanodiamanten eingebettet sind und wobei einer oder mehrere oder alle Diamanten DM bzw. Nanodiamanten dieser Diamanten DM NV-Zentren NVZ und/oder andere paramagnetischen Zentren aufweisen und wobei die NV-Zentren NVZ des Trägermaterials TM und/oder die anderen paramagnetischen Zentren des Trägermaterials TM bei Bestrahlung mit Pumpstrahlung LB zumindest eine Fluoreszenzstrahlung FL emittieren;
• • Benetzen 150 des ersten Endes des Lichtwellenleiters TM auf eine Benetzungslänge L_B mit dem Trägermaterial TM, das die Vielzahl eingebetteter Diamanten DM bzw. Nanodiamanten aufweist;
• • Einspeisen 155 elektromagnetischer Strahlung in das zweite Ende ELWL2 des Lichtwellenleiters LWL, wobei die Wellenlänge dieser elektromagnetischen Strahlung, die Aushärtewellenlänge λ_H so gewählt ist, dass das Trägermaterial TM am zweiten Ende ELWL2 des Lichtwellenleiters LWL aushärtet und sich in einen Festkörper wandelt, wobei das ausgehärtete Trägermaterial TM das Sensorelement NV ausbildet;
• • Entfernen 160 des nicht ausgehärteten Trägermaterials TM insbesondere mittels eines Lösungsmittels, wobei der verbleibende Film des Trägermaterials TM am ersten Ende des Lichtwellenleiters LWL das Sensorelement bildet;
• • Bereitstellen 165 eines Sensorkopfgehäuses GH des Sensorkopfes SK und einer Erregungsquelle für eine magnetische Erregung H, insbesondere eines Permanentmagneten PM;
• • Einbau 170 des Lichtwellenleiters LWL mit dem neu gebildeten Sensorelement NV in den Kanal KN des Sensorkopfgehäuses GH des Sensorkopfes SK und Einbau der einer Erregungsquelle für eine magnetische Erregung H in das Sensorkopfgehäuses GH des Sensorkopfes SK;
• • Verwendung 180 des Sensorkopfes SK zur ortsaufgelösten Vermessung der magnetischen Eigenschaften des Materials eines Werkstücks in der Nähe der Oberfläche OF des Werkstücks, wobei die Ortsauflösung besser als 500µm und/oder besser als 200µm und/oder besser als 100µm und/oder besser als 50µm und/oder besser als 20µm und/oder besser als 10µm ist. Dabei ist Auflösung die Möglichkeit zwei beieinanderliegende Störungen der magnetischen Eigenschaften einer Oberfläche OF eines Werkstücks noch durch ein Extremum von 5% der Signalamplitude zu können, wenn diese entsprechend der Auflösung voneinander beabstandet sind. Solche Störungen können beispielsweise Risse, Lunker, Materialinhomogenitäten etc. sein.

6 shows the steps of the method for producing a proposed sensor head SK and its use. The method comprises the steps:

• • Providing 140 an optical waveguide LWL, wherein the optical waveguide LWL has a first end ELWL1 and a second end ELWL2;
• • Providing 145 a liquid carrier material TM that can be hardened by means of electromagnetic radiation of a curing wavelength λ _H , wherein a plurality of diamonds DM or nanodiamonds are embedded in the carrier material (TM) and wherein one or several or all 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 carrier material TM and/or the other paramagnetic centers of the carrier material TM emit at least one fluorescent radiation FL when irradiated with pump radiation LB;
• • Wetting 150 the first end of the optical waveguide TM to a wetting length L _B with the carrier material TM having the plurality of embedded diamonds DM or nanodiamonds;
• • feeding 155 electromagnetic radiation into the second end ELWL2 of the optical waveguide LWL, wherein the wavelength of this electromagnetic radiation, the curing wavelength λ _H , is selected such that the carrier material TM hardens at the second end ELWL2 of the optical waveguide LWL and turns into a solid, wherein the hardened carrier material TM forms the sensor element NV;
• • Removing 160 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 waveguide LWL forms the sensor element;
• • 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 waveguide LWL with the newly formed sensor element NV in 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 in the sensor head housing GH of the sensor head SK;
• • Use 180 of the sensor head SK for spatially resolved measurement of the magnetic properties of the material of a workpiece in the vicinity of the surface OF of the workpiece, 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. Resolution is the ability to detect two adjacent disturbances in the magnetic properties of a surface OF of a workpiece by an extremum of 5% of the signal amplitude if they are spaced apart from each other in accordance with the resolution. Such disturbances can be, for example, cracks, cavities, material inhomogeneities, etc.

Figure 7

7a shows an example workpiece made of a ferromagnetic material FM in a top view. Various holes L1 to L3 are made in the surface of the workpiece as a simulation of a crack RI. The first hole L1 should have an example diameter of 4mm, for example. The second hole L2 should have an example diameter of 3mm, for example. The third hole L3 should have an example diameter of 2mm, for example.

For the creation of the 7b A sensor head SK was used as shown in the 4 and 5 shown, was displaced over the surface OF of the workpiece along the path indicated by x, while maintaining contact between the support surface AF and the surface OF of the workpiece.

The value curve of the measurement signal S4 obtained in this way is shown in the 7b as a function of the position x of the sensor head SK on the surface OF. Due to the small size D _LWL of the sensor element NV, the spatial resolution is considerable, which is unknown in the state of the art.

List of reference symbols

140

Providing 140 an optical waveguide LWL, the optical waveguide LWL having a first end ELWL1 and a second end ELWL2;

142

Providing 142 a liquid carrier material TM which can be hardened by means of electromagnetic radiation of a curing wavelength λ _H , wherein a plurality of diamonds DM, preferably nanodiamonds, are embedded in the carrier material TM and wherein one or several or all diamonds DM 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 carrier material TM and/or the other paramagnetic centers of the diamonds DM of the carrier material TM emit at least one fluorescence radiation FL when irradiated with pump radiation LB;

145

Providing 145 a liquid carrier material TM which can be hardened by means of electromagnetic radiation of a curing wavelength λ _H , wherein a plurality of diamonds DM or nanodiamonds are embedded in the carrier material (TM) and wherein one or several or all 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 carrier material TM and/or the other paramagnetic centers of the carrier material TM emit at least one fluorescent radiation FL when irradiated with pump radiation LB;

150

Wetting 150 the first end of the optical waveguide TM to a wetting length L _B with the carrier material TM having the plurality of embedded diamonds DM or nanodiamonds;

155

Feeding 155 electromagnetic radiation into the second end ELWL2 of the optical waveguide LWL, wherein the wavelength of this electromagnetic radiation, the curing wavelength A _H, is selected such that the carrier material TM hardens at the second end ELWL2 of the optical waveguide LWL and turns into a solid, wherein the hardened carrier material TM forms the sensor element NV;

160

Removing 160 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 waveguide LWL forms the sensor element;

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 in 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 in 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 the material of a workpiece in the vicinity of 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 the ability to detect two adjacent disturbances in the magnetic properties of a surface OF of a workpiece by an extremum of 5% of the signal amplitude if they are spaced apart from each other in accordance with the resolution. Such disturbances can be, for example, cracks, cavities, material inhomogeneities, etc.

α

Angle formed by the optical fiber LWL with the support surface AF in the immediate vicinity of the sensor element NV;

β

Angle between the virtual perpendicular AFS to the support surface AF of the sensor head SK on the one hand and the optical fiber LWL as it exits the sensor head housing GH of the sensor head SK. The angle β is preferably 90°. This has the advantage that such an angle β minimizes the torque that the optical fiber LWL together with its mechanical sheath 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. The value of β is preferably 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

Support surface of the sensor head SK;

AFS

virtual perpendicular to the support 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;

dl

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 the second or the common optical fiber LWL;

dpm

Distance d _pm of the lower end of the permanent magnet PM to the support surface AF;

dr

Thickness at other points of the end face EF of the first end ELWL1 of the first and/or second or common optical waveguide LWL;

dSK1

Height of the sensor head SK;

dSK2

Length of the sensor head SK;

dSK3

Width of the sensor head SK;

dSK4

Depth of the recess VT of the sensor head SK;

DLWL

Diameter of the optical fiber LWL;

DLWLL

Diameter of the optical fiber lens LWLL;

DLWLMH

Diameter of the sheathed optical fiber LWL comprising the diameter of the optical fiber LWL with the mechanical sheath 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 face of the first end ELWL1 of the first and/or second or common optical waveguide 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 means of 3D printing, for example by means of FDM or SLS printing. Preferably, the material of the sensor head housing is not ferromagnetic (µ _t <1) at least in the vicinity of the sensor element NV. 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;

CN

Channel KN through which the optical fiber LWL is introduced into the sensor head housing GH;

LB

wetting length;

LB

pump radiation;

LIV

lock-in amplifier;

LWL

Optical fiber. Preferably a glass fiber;

LWLC

Core of the optical fiber LWL;

LWLL

optical fiber lens;

λfl

fluorescence wavelength;

λH

Curing wavelength;

λpmp

pump radiation wavelength;

M1

multiplier;

MH

mechanical casing;

ML

Center line of the optical fiber LWL (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. The sensor element preferably comprises a plurality of nanodiamonds or diamonds DM that are differently oriented and preferably have a plurality of NV centers NVZ. The sensor element with the diamonds DM or nanodiamonds is preferably placed 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<<<

CN

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. The permanent magnet is preferably 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 interaction with the material of the workpiece near the surface OF of the workpiece and near the sensor element NV. Instead of a permanent magnet, a current-carrying coil or the like can also be used here. More complicated magnetic circuits with more than one source of magnetic excitation are also conceivable. For example, the sensor head SK can also have 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 the magnetic excitation H. In the context of the document presented here, the term permanent magnet refers to any structured source of magnetic excitation H. However, a single permanent magnet is expressly preferred;

RI

Disturbance in the ferromagnetic material FM. Such a disturbance may be a change in composition that locally changes the magnetic properties of the ferromagnetic material FM. For example, it may be a crack or a void or a hole or a depression or 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

transmission signal;

S5w

pre-transmission signal;

SCR

Screw. The sensor head housing GH preferably has a thread for a grub screw for fixing the optical fiber LWL to accommodate the screw;

ss

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 guiding finger of a hand;

List of cited writings

• EN 10 2019 120 076 A1 ,
• EN 11 2020 003 569 A5 ,
• EN 11 2020 004 650 A5 ,
• EN 10 2020 109 477 A1
• EN 10 2021101 565 A1 ,
• EN 10 2021 114 589.9 ,
• EN 10 2022 121 444.3 ,
• EN 10 2022 122 505.7 ,
• EP 3 874 343 A2

Claims (25)

Sensor head (SK), with a sensor element (NV), wherein the sensor element (NV) comprises a plurality 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 waveguide (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 support surface (AF) and wherein the optical waveguide (LWL) with the sensor element (NV) is installed in the sensor head housing (GH) at an angle (α) to the support surface (AF) of the sensor head (SK) between 10° and 70° and wherein the sensor element (NV) is located at a distance from the support 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 support surface (AF) of the sensor head (SK) of 45° to 135° and/or 70° to 110° and/or 80° to 100° and/or 85° to 95°' and/or 87° to 93°. Sensor head (SK), with a sensor element (NV), wherein the sensor element (NV) comprises a plurality 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 waveguide (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 electrical 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 support surface (AF), and wherein the optical fiber (LWL) with the sensor element (NV) is installed in the sensor head housing (GH), and wherein the sensor element (NV) is located at a distance from the support surface (AF) which is smaller than the diameter (D _LWLMH ) of the coated optical fiber (LWL), and wherein the sensor element (NV) is located on or at least near the extension of the axis (AX). Sensor head (SK) according to Claim 2 , wherein the sensor head (SK) comprises a ferromagnetic support (ST) or another ferromagnetic device element of the sensor head (SK) which are different from the permanent magnet (PM) and/or the electrical coil. Sensor head (SK) according to Claim 3 , wherein the ferromagnetic support (ST) with the permanent magnet (PM) and/or the electric coil are device parts of a magnetic circuit and wherein the magnetic excitation (H) causes a magnetic flux (B) in the magnetic circuit and wherein this magnetic flux (B) flows through the sensor element (NV) and the surface (OF) of a material of the workpiece, a ferromagnetic material (FM) of the workpiece, and wherein spatial fluctuations in the magnetic properties of the material of the workpiece in the vicinity of the surface (OF) influence the intensity of a fluorescent radiation FL of the sensor element (NV). Sensor head (SK) according to Claim 3 or 4 , wherein the ferromagnetic support (ST) is tubular with a second axis. Sensor head (SK) according to Claim 5 , wherein the second axis of the ferromagnetic support (ST) is substantially parallel to the axis (AX) of the permanent magnet (PM). Sensor head (SK) according to one of the Claims 3 until 6 , wherein the ferromagnetic support (ST) has an opening (OE) for the optical waveguide (LWL) in the ferromagnetic support (ST); Sensor head (SK) according to Claim 7 , wherein the opening (OE) is part of a channel (KN) within the sensor head (SK) in which the optical fiber (LWL) is mounted. Sensor head (SK) according to one of the Claims 3 until 8th , 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). Sensor head (SK) according to one of the Claims 3 until 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). Sensor head (SK) according to one of the Claims 2 until 10 , wherein the sensor element (NV) comprises an optical waveguide lens (LWLL), and wherein the optical waveguide lens (LWLL) comprises a plurality of diamonds (DM) and/or nanodiamonds with NV centers (NVZ) and/or paramagnetic centers, and wherein the optical waveguide lens (LWLL) is located at a first end (ELWL1) of the optical waveguide (LWL), and wherein the optical waveguide lens (LWLL) has a diameter (D _LWLL ) of the optical waveguide lens (LWLL) that is smaller than the diameter (D _LWL ) of the optical waveguide (LWL). Sensor head (SK), with a sensor element (NV), wherein the sensor element (NV) comprises a plurality 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 waveguide (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 electrical coil as a source of magnetic excitation (H) and wherein the sensor element (NV) comprises an optical waveguide lens (LWLL) and wherein the optical waveguide lens (LWLL) comprises a plurality of diamonds (DM) and/or nanodiamonds with NV centers (NVZ) and/or paramagnetic centers and wherein the optical waveguide lens (LWLL) is located at a first end (ELWL1) of the optical waveguide (LWL) and wherein the optical waveguide lens (LWLL) has a diameter (D _LWLL ) of the optical waveguide lens (LWLL) which is smaller than the diameter (D _LWL ) of the optical waveguide (LWL). Sensor head (SK) according to Claim 12 , wherein the permanent magnet (PM) and/or the electric 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. Sensor head (SK) according to Claim 12 or Claim 13 , wherein the sensor head (SK) has a sensor head housing (GH) with a support surface (AF), and wherein the optical waveguide (LWL) with the sensor element (NV) is installed in the sensor head housing (GH), and wherein the sensor element (NV) is located at a distance from the support surface (AF) which is smaller than the diameter (D _LWLMH ) of the coated optical waveguide (LWL), and wherein the sensor element (NV) is located on or at least near the extension of the axis (AX). Sensor head (SK) according to one of the Claims 12 until 14 , wherein the sensor head (SK) comprises a ferromagnetic support (ST) or another ferromagnetic device element of the sensor head (SK) which are different from the permanent magnet (PM) and/or the electrical coil. Sensor head (SK) according to Claim 15 , wherein the ferromagnetic support (ST) with the permanent magnet (PM) and/or the electric coil are device parts of a magnetic circuit and wherein the magnetic excitation (H) causes a magnetic flux (B) in the magnetic circuit and wherein this magnetic flux (B) flows through the sensor element (NV) and the surface (OF) of a material of the workpiece, a ferromagnetic material (FM) of the workpiece, and wherein spatial fluctuations in the magnetic properties of the material of the workpiece in the vicinity of the surface (OF) influence the intensity of a fluorescent radiation FL of the sensor element (NV). Sensor head (SK) according to Claim 15 or 16 , wherein the ferromagnetic support (ST) is tubular with a second axis. Sensor head (SK) according to Claim 17 , wherein the second axis of the ferromagnetic support (ST) is substantially parallel to the axis (AX) of the permanent magnet (PM). Sensor head (SK) according to one of the Claims 15 until 18 , wherein the ferromagnetic support (ST) has an opening (OE) for the optical waveguide (LWL) in the ferromagnetic support (ST); Sensor head (SK) according to Claim 19 , wherein the opening (OE) is part of a channel (KN) within the sensor head (SK) in which the optical fiber (LWL) is mounted. Sensor head (SK) according to one of the Claims 15 until 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). Sensor head (SK) according to one of the Claims 15 until 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). 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 of placing a sensor head (SK), according to one or more of the Claims 1 until 22 , with a support 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 recording the values of a flux density measurement signal (S4) which depends on the intensity of the fluorescence radiation (FL) from NV centers (NVZ) and/or paramagnetic centers in diamonds of a sensor element (NV) of the sensor head (SK); concluding that there is a fault 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. Procedure according to Claim 23 , wherein the displacement of the sensor head (SK) on the surface (OF) of the workpiece parallel to the surface (OF) of the workpiece along a path (x) and the simultaneous detection of the values of the flux density measurement signal (S4) comprise a simultaneous detection and/or estimation of one or more coordinates of the location of the sensor head (SK) or an equivalent value at the time of detection of a value of the flux density measurement signal (S4). Procedure according to Claim 24 , Displaying the values of the flux density measurement signal (S4) as a function of the respectively recorded coordinates on a screen and/or providing data for such a display.

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