DE102011050717A1 - Fiber-optic sensor such as fiber Bragg sensor of measuring system for measuring load on e.g. building, has protective coating that is provided on portion of magnetostrictive layer - Google Patents

Abstract

A fiber optic sensor (100, 200, 300, 400, 500) is specified. The fiber optic sensor (100, 200, 300, 400, 500) comprises an optically conductive fiber core (110, 210, 310, 410), an electrically conductive layer (140, 240, 340, 440), which at least the optically conductive fiber core a portion (455, 555) surrounds and a magnetostrictive layer (150, 250, 350, 450) electroplated onto the electrically conductive layer (140, 240, 340, 440). In addition, a manufacturing method and a validation method for a fiber optic sensor (100, 200, 300, 400, 500) and a measuring system (600, 6001) for validating a fiber optic sensor (100, 200, 300, 400) embedded in a test specimen (700) are described , 500).

Description

The present invention relates to a fiber optic sensor, in particular a fiber optic position or strain sensor, an associated manufacturing method, a validation method for the fiber optic sensor and an associated measuring device.

Fiber optic sensors are increasingly playing a role in the monitoring of components and structures that are exposed to dynamic loads. The objects to be monitored may be, for example, machine parts or plant parts with sometimes considerable expansions, such as aircraft wings, fuselages, rotor blades or towers of wind turbines. Even such extensive structures as buildings, bridges, dams or dykes can be monitored with fiber optic sensors. In this case, the fiber optic sensors are used in particular for length or strain measurement, since transmission properties of the fiber, e.g. the backscatter properties of the fiber, different for different strain states. Typically, backscatter measurement methods are used for such investigations. These backscatter measuring methods allow to detect a local distribution of the measured variable along the fiber. Among the backscatter measurement methods, the optical backscatter measurement in the time domain, also known as OTDR ("Optical Time Domain Reflectometry"), is probably the most widespread measurement technique. In addition to time domain analysis (OTDR), those skilled in the art are also familiar with correlation range analysis and frequency domain analysis as backscatter measurement methods. Thus, by measuring the elongation of an optical fiber by Brillouin frequency domain analysis, changes in components and structures can be detected. In addition, fiber optic strain sensors may be implemented as interferometric sensors or based on light intensity of a light signal reflected or transmitted by the optical fiber that varies with the elongation of the fiber. For example, strains can be measured with high frequency and accuracy by means of the known fiber Bragg gratings (FBG). Furthermore, fiber-optic sensors based on direct phase measurement of an intensity-modulated signal in transmission are known. These systems are also capable of high-frequency and accurate measure length changes.

Typically, glass fibers are used as fiber optic strain sensors, particularly in the range of strains of up to about 1%. Sensors based on optical polymer fibers, in short POF (English: Polymer Optical Fiber), are also suitable for strain measurement for strains of more than 45%.

However, the reliable detection of changes such as strains in components and structures over long or long periods up to several years or even up to several decades requires correspondingly reliable and long-term stable integrated fiber optic sensors. However, such validation methods have not yet been developed for integrated fiber optic sensors, which currently limits their use in the monitoring of components and structures.

In view of the above, the present invention proposes a fiber optic sensor according to claim 1, a manufacturing method according to claim 9, a measuring system according to claim 13 and a method for validating a fiber optic sensor according to claim 17.

According to one embodiment, a fiber optic sensor is provided. The fiber optic sensor comprises an optically conductive fiber core, e.g. of glass or a suitable polymer, an electrically conductive layer and a magnetostrictive layer electroplated onto the electrically conductive layer. The electrically conductive layer surrounds the optically conductive fiber core in at least one section. Typically, the fiber optic sensor is a strain sensor and / or a length sensor that can be embedded in a specimen. This allows easy monitoring of mechanical changes in the specimen. By applying magnetic fields, it is also possible to characterize the bond between the fiber optic sensor and the specimen. This allows measurements on the specimen with a validated fiber optic sensor. The specimen may be a machine, a machine part, a component or a building.

According to a development of the fiber optic sensor is designed as a fiber Bragg sensor, Fabry-Perot sensor, Raman sensor, Brillouin sensor or Rayleigh sensor. With such a fiber optic sensor changes in length or expansions of the specimen can be detected highly sensitive. For example, the optically conductive fiber core may have a fiber Bragg grating in the at least one portion.

According to a further development, the magnetostrictive layer comprises a nickel-iron alloy, a nickel-cobalt alloy, a nickel-iron-cobalt alloy, or an iron-cobalt alloy. Magnetostrictive layers of these materials have high magnetostriction. Thus, at typical layer thicknesses of the magnetostrictive layer in a range from about 2 microns to about 200 microns, more typically in a range of about 4 microns up to 100 microns, more typically in a range of about 5 microns to 50 microns, with relatively weak magnetic fields of up to a few mT - depending on the state of the composite between fiber optic sensor and specimen - optically relatively easily detectable changes in length of the fiber optic sensor are generated, and thus characterizing the bond between fiber optic sensor and specimen. In addition, nickel-iron alloy, nickel-cobalt alloy, nickel-iron-cobalt alloy, and iron-cobalt alloy can be electrodeposited well on the electrically conductive layer, which may be formed by, for example, copper, a copper alloy, or gold.

According to a further development, the electrically conductive layer is applied to a bonding agent layer in order to ensure a stable bond of the fiber-optic sensor. For example, an adhesion promoter layer of chromium or titanium may be provided between a glass fiber core or a fiber cladding layer of glass and an electrically conductive layer of copper or gold.

The composition of the magnetostrictive layer may also be chosen such that its thermal expansion coefficient is adapted to the material of the optically conductive fiber core and / or the material of a fiber cladding and / or the material of the specimen. As a result, thermal stresses can be at least reduced with temperature fluctuations. For nickel-iron alloy as a magnetostrictive layer, the nickel content may be e.g. in a range of about 20% to about 70% or even in a range of about 10% to 90%. For a fiber optic fiber optic sensor, a nickel content of the nickel-iron alloy as the magnetostrictive layer may be selected in a range of about 25% to 35% to allow particularly good thermal matching of the magnetostrictive layer to the glass fiber.

According to a further development, the fiber-optic sensor comprises an integrated coil, wherein the fiber-optic sensor and the integrated coil are integrally formed. Such a sensor can also be easily embedded in the specimen. In addition, the integrated coil can be used to generate a magnetic field so that no external magnetic field source is needed to validate the embedded fiber optic sensor.

According to one embodiment, a method of manufacturing a fiber optic sensor is provided. An optical fiber comprising at least one optically conductive fiber core is provided. An electrically conductive layer is applied so that the optically conductive fiber core is surrounded by the electrically conductive layer at least in one section. On the electrically conductive layer, a magnetostrictive layer is produced galvanically. The galvanic generation allows a simple variation of the layer thickness and a simple structuring of the magnetostrictive layer in the direction of the fiber axis of the optically conductive fiber core.

According to a development, the method comprises the application of a bonding agent layer before the electrically conductive layer is applied. Thereby, the adhesive bond between the optical fiber and the magnetostrictive layer can be improved.

According to a further development, the method comprises the application of a further electrically conductive layer for producing an integrated coil after which the magnetostrictive layer has been produced. This may provide a fiber optic sensor that does not require an external magnetic field source for its validation.

Typically, the electrically conductive layer, the further electrically conductive layer and / or the adhesion promoter layer are produced by means of a sputtering process.

According to one exemplary embodiment, a measuring system is provided for validating a fiber optic sensor with a magnetostrictive layer embedded in a test specimen. Typically, the fiber optic sensor is laminated, glued or cast into the specimen. The measuring system comprises a light source coupled to the fiber optic sensor for generating a light signal, e.g. a laser. The measuring system also comprises a switchable magnetic field source, at least one detector coupled to the fiber optic sensor, and an evaluation unit. The magnetic field source is set up to expose at least the magnetostrictive layer to a magnetic field. The evaluation unit is set up to detect a change in a transmission characteristic of the fiber-optic sensor for the light signal when the magnetic field changes and to determine therefrom an embedding state of the fiber-optic sensor in the test body. The embedded state of the fiber optic sensor can be used to calibrate the fiber optic sensor. This allows calibrated length and / or strain measurements of the specimen by means of the fiber optic sensor.

According to a development, the switchable magnetic field source is arranged between an optically conductive fiber core of the fiber-optic sensor and the test body, so that no external switchable magnetic field source is needed. For example, the fiber optic sensor is a fiber optic sensor with an integrated coil embedded together in the specimen.

According to a further development, a proportion of a backscattered from the fiber optic sensor wavelength of the light signal is used as a transmission property of the fiber optic sensor. Thus, sensitive and reliable length and / or strain measurements of the specimen are possible. The fiber optic sensor may be a fiber Bragg sensor, i. a fiber optic sensor with a fiber Bragg grating. But it is also possible that the fiber optic sensor is a Fabry-Perot sensor, a Raman sensor, a Brillouin sensor or a Rayleigh sensor.

According to one embodiment, a method for validating a fiber optic sensor is provided. The method has the step of embedding the fiber optic sensor in a test specimen. In this case, the fiber-optic sensor is embedded in such a way that at least part of a magnetostrictive layer of the fiber-optic sensor is located in the test body. Typically, embedding involves a process of lamination and / or a process of sticking and / or a process of pouring. In addition, the method includes the steps of determining a first signal of the fiber optic sensor, changing a magnetic field exposure of the magnetostrictive layer, determining a second signal of the fiber optic sensor during the changed magnetic field exposure, and determining an embedding state of the fiber optic sensor. Determining an embedding state, e.g. an adhesive bond, between the fiber optic sensor and the specimen, comprises comparing the first signal and the second signal. This provides a simple and reliable method of validating the fiber optic sensor.

Typically, the first and second signals represent a transmission characteristic of the embedded fiber optic sensor. This allows calibration of the embedded fiber optic sensor.

According to a development, the method comprises a subsequent measurement of a length and / or elongation of the test specimen with the calibrated embedded fiber optic sensor. This allows a simple and reliable monitoring of the specimen.

Further advantageous embodiments, details, aspects and features of the present invention will become apparent from the dependent claims, the description and the accompanying drawings. It shows:

1 a schematic perspective view of a fiber optic sensor according to an embodiment;

2 a schematic perspective view of a fiber optic sensor according to another embodiment;

3 a schematic perspective view of a fiber optic sensor according to yet another embodiment;

4 a schematic perspective view of a fiber optic sensor according to yet another embodiment;

5 a schematic representation of a measuring device according to an embodiment;

6 a schematic representation of a measuring device according to another embodiment;

7 Measurements of the change of the Bragg wavelength in magnetic field exposure with a fiber optic sensor according to an embodiment;

8th Normalized measurements of the variation of the Bragg wavelength as a function of the temperature with a fiber optic sensor according to an embodiment;

9 Steps of a method of manufacturing a fiber optic sensor according to an embodiment; and

10 Steps of a method for validating a fiber optic sensor according to an embodiment.

1 shows a fiber optic sensor 100 according to an embodiment in a schematic perspective view. The fiber optic sensor 100 has an optically conductive fiber core 110 , 1 shows the typically flexible fiber optic sensor 100 in a non-bent state, in which the optically conductive fiber core 110 a cylinder with a diameter d1 of eg 6 μm, 10 μm for singlemode fibers or 50 μm, 62.5 μm or 100 μm for multimode fibers and a central fiber axis 190 forms. To the optically conductive fiber core 110 is a hollow cylindrical fiber cladding 120 arranged with an outer diameter d2 of typically 125 microns. The following is the optically conductive fiber core 110 also called fiber core. The fiber core 110 and the fiber cladding 120 can be made of glass or a polymer. The fiber core 110 However, it consists of a visually denser material than fiber cladding 120 ie a material with a higher refractive index, so that a light signal in the fiber core 110 by total reflection between the fiber core 110 and the fiber coat 120 along the fiber axis 190 can spread. On the fiber cladding is an optional adhesive layer 130 applied. If the fiber cladding is made of glass, for example, a thin adhesion promoter layer 130 made of chrome, on which there is an electrically conductive layer 140 , eg a copper layer 140 located. Alternatively, a titanium layer may also be used as adhesion promoter layer 130 for a gold layer as an electrically conductive layer 140 be used. The primer layer 130 may be only a few nanometers (nm) thin, eg about 2 nm or even only about 1 nm. In these embodiments, the outer diameter is d3 of the primer layer 130 only slightly larger than the outer diameter d2 of the fiber cladding 120 , The layer thickness of the electrically conductive layer 140 ie the difference between the outer diameter d4 of the electrically conductive layer 140 and the outer diameter d3 of the primer layer 130 , may be up to a few microns, but also less than 1 micron, for example, about 10 nm, be. The primer layer 130 ensures a firm bond between the fiber cladding and the electrically conductive layer 140 ,

On the electrically conductive layer 140 there is a galvanized magnetostrictive layer 150 , in turn, from a protective coating ("coating"). 160 surrounded with an outer diameter d6 of eg 250 microns. Typically, the fiber optic sensor has 100 in the radial direction in at least one section along the fiber axis 190 the in 1 schematically illustrated construction. In other sections, the fiber optic sensor has 100 typically a conventional construction, wherein the fiber cladding 120 is surrounded directly by the protective coating. The magnetostrictive layer 150 is thus typically only in one or more sections along the fiber axis 190 intended. These sections are also referred to below as magnetic-field-sensitive sections. The magnetic field sensitive sections have in the direction of the fiber axis 190 a length of typically about 0.1 mm to about 10 cm, more typically a length of about 1 mm to about 1 cm, for example a length of about 10 mm.

If the fiber optic sensor 100 with the magnetostrictive layer 150 embedded sections or sections in a test specimen, so by applying a magnetic field, ie by magnetic field exposure of the magnetostrictive layer 150 , a force between the specimen and the fiber core 110 in the direction of the fiber axis 190 be exercised provided the fiber optic sensor 100 is sufficiently well embedded in the sample. This is caused by the magnetostrictive effect resulting in a change in the length of the magnetostrictive layer 150 in the direction of the fiber axis 190 can lead. This can also be a length of the fiber core 110 in the direction of the fiber axis 190 to be changed. Depending on the material of the magnetostrictive layer, relative wavelength changes in a range of up to 30 μm / m and beyond can be achieved. Also, such a change in the length of the fiber core 110 can be detected optically well. This can be the fiber core 110 For example, have fiber Bragg gratings. As a sensitive element in addition to fiber Bragg gratings and other optical strain sensors such as a Fabry-Perot interferometer can be used. The fiber optic sensor 100 However, it can also be set up for an optical strain measurement with distributed sensor technology, eg via Brillouin, Raman, or Rayleigh backscatter.

If and how far we go the length of the fiber core 110 in the direction of the fiber axis 190 When applying or changing a magnetic field changes depends not only on the magnetic field properties and the structure but also on the embedding state of the fiber-optic sensor in the specimen, for example, from the adhesive bond between the fiber-optic sensor and the specimen. By applying or varying magnetic fields, a simple characterization of the embedding state or adhesive state of the fiber-optic sensor can thus be carried out after it has been embedded in the test specimen. This also allows calibration of the fiber optic sensor 100 and thus calibrated length or strain measurements by means of the fiber optic sensor 100 , Thus, the systematic source of error of the embedding state of previous length and strain measurements with embedded fiber optic sensors can be minimized or even eliminated.

Typically, the magnetostrictive layer exists 150 from a nickel-iron alloy, a nickel-cobalt alloy, a nickel-iron-cobalt alloy, an iron-cobalt alloy, or a layer sequence of these materials. On the one hand, these materials show a sufficiently high magnetostrictive effect. As a result, optically well detectable changes in length of the fiber optic sensor can be 100 Both with high magnetic field strengths into the Tesla range as well as with moderate magnetic field strengths of up to a few mT or even with low magnetic field strengths of less than one mT achieve. On the other hand, they are good electrodepositable, so that the fiber optic sensor 100 just in the direction of its fiber axis 190 can be structured. The layer thickness of the magnetostrictive layer 140 , ie the difference between the outer diameter d5 of magnetostrictive layer 140 and the outer diameter d4 of the electrically conductive layer 140 is typically in the range of about 1 μm to about 100 μm, more typically in the range of about 5 μm to about 50 μm.

The nickel content of the magnetostrictive layer 150 For example, nickel-iron alloy may range from about 10% to about 90%, eg about 70%. In addition, the composition of the magnetostrictive layer 150 be adapted in terms of their thermal expansion coefficient of the material of the fiber core or the fiber cladding in order to reduce or minimize thermal stresses at changing temperatures of the specimen. For example, the nickel content of the nickel-iron alloy of the magnetostrictive layer 150 be in a range of about 25% to 35%, for example, about 30%, and so to allow a good adaptation to glass as a fiber material in terms of thermal expansion coefficients.

2 shows a fiber optic sensor 200 according to an embodiment in a schematic perspective view. The fiber optic sensor 200 resembles the fiber optic sensor 100 and is also externally with a protective coating 260 Mistake. The fiber optic sensor 200 However, at least in its magnetic field-sensitive sections has no fiber cladding. Accordingly, the magnetostrictive layer 250 of the fiber optic sensor 200 at least in the magnetic field sensitive sections via an optional adhesion promoter layer 230 and an electrically conductive layer 240 with the fiber core 210 connected. As the adhesive layer 230 or the electrically conductive layer 240 As metallic layers are highly reflective, the optical signal line is along the fiber axis 290 also ensured without fiber cladding. Due to the lack of fiber cladding, but mechanical stresses of the magnetostrictive layer 250 typically stronger on the fiber core 210 transferred and this typically deformed when applying or changing a magnetic field stronger. This allows a more sensitive characterization of the embedded state of the fiber optic sensor 200 in the test piece.

3 shows a fiber optic sensor 300 according to an embodiment in a schematic perspective view. The fiber optic sensor 300 resembles the fiber optic sensor 100 , In a magnetic field sensitive section 355 however, it is not a protective coating 360 provided or by an optional adhesive layer 330 , an electrically conductive layer 340 and a magnetostrictive layer 250 completely replaced. In this embodiment, the outer diameter d5 corresponds to the magnetostrictive layer 250 in the magnetic field-sensitive section 355 the outer diameter d6 of the protective coating 360 of the fiber optic sensor 300 in sections, in the radial direction from a conventional sequence of fiber core 310 , Fiber coat 320 and protective coating 360 consist. In the magnetic field sensitive section 355 is the fiber optic sensor in the radial direction as a sequence of fiber core 310 , Fiber coat 320 , optional adhesive layer 330 , electrically conductive layer 340 and magnetostrictive layer 250 built up. In the embedded state, the magnetostrictive layer is adjacent 250 of the fiber optic sensor 300 typically directly to the matrix material of the specimen, so that mechanical stresses between the magnetostrictive layer 250 and the specimen can not be partially degraded by the fiber cladding when applying or changing a magnetic field.

This typically allows a more sensitive characterization of the embedded state of the fiber optic sensor 300 ,

According to a further embodiment - as with reference to 2 explained - in the magnetic field-sensitive section 355 also on the fiber coat 320 waived. Thus, mechanical stresses of the magnetostrictive layer 350 when applying or changing a magnetic field is typically stronger on the fiber core 310 transferable. This typically allows even more sensitive characterization of the embedded state of the fiber optic sensor 300 ,

4 shows a fiber optic sensor 400 according to an embodiment in a schematic cross section along the fiber axis 490 , The fiber optic sensor 400 resembles the fiber optic sensor 300 , As with this is the fiber optic sensor 400 a protective coating 460 only outside of a magnetic field-sensitive section 455 intended. Also, in the fiber optic sensor 400 a coil 480 integrated. Typically, the fiber optic sensor 400 and the coil 480 integrally formed. They can therefore be easily embedded together in a test specimen. In addition, a magnetic field can be generated and / or modulated by the integrated coil, at least the magnetic field-sensitive section 455 is exposed. For validating or calibrating the fiber optic sensor 400 Therefore, no external magnetic field source is needed. The fiber optic sensor 400 can thus also be used for long-term monitoring of components or machine parts, in which the cost of external magnetic field sources is relatively high. This may be the case, for example, in the case of extended and / or elongated specimens such as buildings, roads or dykes but also in rotating machine parts.

In one embodiment, the fiber optic sensor is 400 in the magnetic field-sensitive section 455 in the radial direction as a sequence of a fiber core 410 , a fiber coat 420 , an electrically conductive layer 440 a magnetostrictive layer 450 and an insulating layer 470 , eg a polymer layer 470 , educated. The insulating layer 470 typically closes flush with the protective coating 360 the adjacent non-magnetic field sensitive portions of the fiber optic sensor 400 at. The magnetic field sensitive sections may be in the radial direction from a sequence of fiber core 410 , Fiber coat 420 and protective coating 460 consist.

According to yet another embodiment, in the magnetic field sensitive section 455 a variety of coil turns 485 on the insulating layer 470 arranged to be able to generate sufficiently high magnetic fields. For typical dimensions of the magnetic field sensitive section 455 in the direction of the fiber axis 490 of, for example, 10 mm and a pitch of the coil turns of 100 μm or less, 100 or more than 100 coil turns in the magnetic field sensitive portion 455 to be available. The coil turns 485 as well as the coil leads 481 . 482 can be prepared, for example, via a PVD process (physical vapor deposition) and subsequent structuring.

Typically, the magnetostrictive layer 450 on the electrically conductive layer 440 electroplated. Between the electrically conductive layer 440 and the magnetostrictive layer 450 In addition, a primer layer can be provided. As related to the 2 and 3 has been explained, can on the fiber cladding 420 in the magnetic field-sensitive section 455 also be waived.

In other embodiments, the magnetostrictive layer is 450 not galvanized. For example, the magnetostrictive layer 450 on the fiber coat 420 or the electrically conductive layer 440 be produced by sputtering, vapor deposition, PVD method or bonding. It may possibly also on the electrically conductive layer 440 be waived. In these embodiments, the material of the magnetostrictive layer 450 also a not or bad to be galvanized. Thus, materials with particularly high magnetostriction such as terfenol D, magnetic metallic glasses, eg Metglas, and ferrites, such as cobalt ferrite (CoFe ₂ O ₄ ), for the magnetostrictive layer 450 be used.

According to an embodiment, a transmission characteristic of the fiber optic sensor changes 400 at a change in length of the magnetic field sensitive section 455 in the direction of the fiber axis 490 , This allows easy validation of the fiber optic sensor 400 , The transmission property may be a transmitted or backscattered or reflected light signal component. For this example, a fiber Bragg grating in the fiber core 410 of the magnetic field sensitive section 455 be arranged.

According to another embodiment, the at least the extent of the magnetostrictive layer increases 450 and the insulating layer 470 in the direction of the fiber axis 460 with increasing distance from the fiber axis 490 , ie in the radial direction, too. In this embodiment, the magnetostrictive layer 450 and the insulating layer 470 in sections along the fiber axis 490 not like in 5 shown, rectangular. This will be the interface to the adjacent protective coating 460 elevated. This allows an even more stable material composite of the fiber optic sensor 400 , Analogous embodiments may also be applied to those with reference to the 1 to 3 be provided explained fiber optic sensors.

5 shows a schematic representation of a measuring device 600 for validating one in a test specimen 700 embedded fiber optic sensor 500 according to an embodiment. In the fiber optic sensor 500 it can be a fiber optic sensor as it relates to the 1 to 4 was explained. In particular, the fiber optic sensor has 500 a magnetostrictive layer. Typically, the magnetostrictive layer is in a magnetically sensitive portion of the fiber optic sensor 500 arranged, at least partially, for example, completely, in the specimen 700 is embedded.

The fiber optic sensor 500 is with a light source 610 optically coupled. At the light source 610 it is typically a laser. In the exemplary embodiment of 6 can be a light signal 611 over an optical fiber 601 and an optical coupler 620 , eg a 3dB coupler, at least partially as a light signal 612 into one end of the fiber optic sensor 500 be fed. Depending on the transmission characteristics of the fiber optic sensor 500 can be a backscattered share 613 and / or a transmitted portion 614 the light signal 612 one with the fiber optic sensor 500 coupled first detector 630 or second detector 640 be at least partially supplied. In the exemplary embodiment of 6 is the fiber optic sensor 500 via the optical coupler 620 and an optical fiber 602 with the first detector 630 coupled, so this typically a slightly attenuated backscattered light signal 615 can measure. In addition, the fiber optic sensor 500 in the exemplary embodiment of 6 directly with the second detector 640 coupled.

The measuring device 600 has an evaluation unit 650 which is arranged to change a transmission characteristic of the fiber optic sensor 500 for the light signal 611 . 612 upon variation of a magnetic field across the first and / or second detector 630 . 640 to detect and therefrom an embedding state of the fiber optic sensor 500 in the test piece 700 to determine. This is typically done by comparing measured signals of the first and / or second detector 630 . 640 with different magnetic field exposure of the embedded fiber optic sensor 500 ,

The evaluation unit receives this 650 via corresponding signal lines 631 . 641 Data of the first detector 630 and / or the second detector 640 , In addition, the evaluation unit 650 via a signal line 681 with an external switchable magnetic field source 680 be connected to the state of the external magnetic field source 680 to determine and / or control. The evaluation unit 650 So it can also be a combined evaluation and control unit. The external magnetic field source 680 may be configured to generate a modulated, eg a pulsed, magnetic field. Typically, the external magnetic field source comprises one or more coils. In addition, the combined evaluation and control unit 650 via a signal line 651 with the light source 610 be connected to control these. This is a long-term monitoring of the specimen 700 with low power consumption and low data throughputs. For example, appropriate measurements of the measuring device 600 from the combined evaluation and control unit 650 triggered only at greater intervals of minutes, hours, days or at even greater intervals.

According to another embodiment, instead of the external magnetic field source 680 a fiber optic sensor 500 used with integrated coil. In this embodiment, the combined evaluation and control unit 650 over the signal line 681 typically coupled to the integrated coil. It can be provided that the combined evaluation and control unit 650 the integrated coil via the signal line 681 directly drives, ie, the integrated coil supplies suitable electrical supply signals to switch them and / or to modulate the generated magnetic field.

The fiber optic sensor 500 is typically a length sensor and / or a strain sensor. This allows monitoring of the specimen for mechanical changes that may be caused by mechanical and / or thermal stress on the specimen. The fiber optic sensor 500 may be a fiber Bragg sensor, a Fabry-Perot sensor, a Raman sensor, a Brillouin sensor or a Rayleigh sensor. With these fiber optic sensors can be changes in length and / or expansions of the specimen 700 through the measuring device 600 detect highly sensitive. Because the measuring device 600 In addition, it is arranged to characterize the embedding state of the fiber-optic sensor, the length changes and / or expansions of the specimen 700 be carried out calibrated.

6 shows a schematic representation of a measuring device 6001 according to a further embodiment. The measuring device 6001 is similar to the related to 5 explained measuring device 600 , For reasons of clarity are in the measuring device 6001 however, not all connections are shown. When in a in 6 not shown test specimen embedded fiber optic sensor 501 it is a fiber Bragg sensor. In the fiber core 510 of the fiber optic sensor 501 is in an embedded magnetically sensitive area 555 an optical grating 580 arranged with a periodically modulated refractive index. Adjacent maxima of the refractive index have a distance Λ to one another. This also applies to adjacent minima of the refractive index. Now one of a light source 610 a light signal 611 . 612 with a spectrum I (λ), where I (λ) represents the intensity I as a function of the wavelength λ, in the fiber optic sensor 501 coupled, so is part of the light signal 611 . 612 as a light signal 613 . 615 reflected with a narrow band spectrum. The light signal 613 . 615 can be at a first detector 630 be recorded. In this case, the narrow-band spectrum is centered around the so-called Bragg wavelength λ _B , which increases with a mean refractive index n _eff λ _B = 2 · n _eff · Λ results. The spectrum of the transmitted light signal has the Bragg wavelength λ _B correspondingly reduced intensities, resulting in a second detector 640 can be measured. At a given temperature, the Bragg wavelength λ _{B is} directly proportional to the length of the magnetically sensitive region 555 , The determination of the Bragg wavelength λ _B can therefore be based on a length or elongation of the fiber-optic sensor 501 in the embedded magnetically sensitive area 555 getting closed.

In order to be able to distinguish temperature influences from other changes in length of the specimen, eg by cracking, two fiber-optic sensors are typically used, one of the two fiber-optic sensors being mechanically decoupled from the specimen, eg via a glass capillary, and thus being able to be used for independent temperature measurement. Alternatively, two fiber optic sensors with be embedded and measured in the specimen different thermal expansion coefficient.

In the magnetically sensitive area 555 is a magnetostrictive layer integrated, as related to the 1 to 4 was explained. This is in for clarity 6 but also not shown. This can - depending on the embedded state of the fiber optic sensor 501 The length of the magnetically sensitive area 555 be changed by means of a magnetic field. Is the length of the embedded fiber optic sensor 501 changed by an external magnetic field H, the Bragg wavelength λ _{B changes} accordingly. For example, in an evaluation unit 650 a wavelength difference λ _D at different magnetic field expansions of the magnetically sensitive area 555 from the measurements of the first detector 630 and / or the second detector 640 be determined. For example, the wavelength difference λ _D can be determined as the difference between the Bragg wavelengths λ _B when the magnetic field H is switched on and when the magnetic field is switched off (λ _D = λ _B (H) -λ _B (0)) The relative wavelength difference λ _D / λ _B (0) then used as a measure of the embedment state of the fiber optic sensor and thus for its validation. As the relative wavelength difference λ _D / λ _B (0) changes over time, the embedment condition typically deteriorates and the measured strains are to be corrected accordingly. Of course, the relative wavelength difference can also be determined for different magnetic field strengths or differently modulated magnetic fields.

7 FIG. 12 shows exemplary measurements of the change in the Bragg wavelength λ _B at magnetic field exposure obtained with a fiber optic sensor according to an embodiment. The fiber optic sensor is a fiber optic sensor with a basic structure as related to 3 was explained. The layer thickness of the magnetostrictive layer of a nickel-iron alloy with 70% nickel content was about 30 microns. This was produced galvanically on an approximately 7 nm thick electrically conductive layer of copper, which in turn was applied to an approximately 2 nm thick adhesion promoter layer of chromium. The length of the magnetically sensitive region in the direction of the fiber axis was about 10 mm. Fiber core and fiber sheath are made of glass. As can be seen from the illustrated Bragg wavelength λ _B as a function of the measurement i, the changes in length of the fiber-optic sensor can be reproducibly detected as a function of the magnetic field over many measurement cycles. The measurement points at 1544.328 nm correspond to measurements without magnetic field and the measurement points at 1544.331 and at 1544.332 nm to measurements at a magnetic field of about 5 mT, which generates by an RFID coil with pulse frequencies between 4 to 14 Hz has been. The variations of the measurements of the Bragg wavelength at magnetic field exposure are due to the measuring accuracy of the detector of 1 pm (picometer). The response times of the fiber-optic sensor were less than 1 μs, so that it can be magnetically excited high-frequency. Analogous measurement results were obtained in a Helmholtz coil at about 7 mT.

8th shows exemplary measurements of the change in the Bragg wavelength as a function of the temperature T without magnetic field exposure with a fiber optic sensor according to an embodiment. The change of the Bragg wavelength is in relative units, ie as normalized to the Bragg wavelength λ _B0 at the reference temperature (room temperature) difference of Bragg wavelength λ _B and Bragg wavelength λ _B0 at the reference temperature (λ _B - λ _B0 ) / λ _B0 = Δλ _B / λ _B0 indicated. The curve I shows measurements of the fiber optic sensor of the in 7 shown measurements was used. Curve II shows the corresponding measured values for a standard fiber optic sensor as a comparison. The Bragg wavelength λ _B depends linearly on the temperature T for both fiber-optic sensors in a wide temperature range to a good approximation. This simplifies the evaluation of measurements. The temperature sensitivities (compensation lines) for curves I and II were determined to be 6.2 μm / (m K) and 11.2 μm / (m K), respectively. Both fiber optic sensors can thus be used over a wide temperature range.

9 illustrates steps of a procedure 1000 for producing a fiber-optic sensor according to an embodiment. In one step 1100 An optical fiber is provided with at least one optically conductive fiber core. This may be a standard fiber whose fiber core already contains a Bragg grating, for example. In this case, the coating of the standard fiber is removed in at least one section, eg in the section with the Bragg grating. The coating may be beveled in a transition region, which later leads to a firmer bond with adjacent materials due to the larger area. In addition, the beveled, typically cone-shaped, transition region leads to a more homogeneous stress introduction or stress distribution under mechanical loading of the fiber-optic sensor in this area.

In an optional step 1200 An adhesive layer is applied in the at least one section. This can be done, for example, with a sputtering process, for example a PVD process (physical vapor deposition, or "physical vapor deposition"). In one step 1300 becomes one applied electrically conductive layer, which can also be done in a sputtering process. In this way, it is possible, for example, to produce a layer sequence of chromium and copper on a glass fiber cladding, or if this has also been removed in the at least one section, on a glass fiber core. By means of PVD (DC magnetron sputtering), it has been possible to produce layer thicknesses of about 2 nm for chromium layer on glass fiber material and about 7 nm for the copper layer. Larger layer thicknesses can be produced by correspondingly longer PVD steps.

In addition, the electrically conductive layer is typically applied so that the optically conductive fiber core in the at least one portion is completely surrounded by the electrically conductive layer in the radial direction. The electrically conductive layer may be e.g. be deposited as a hollow cylinder.

The following will be in one step 1400 galvanically a magnetostrictive layer on the electrically conductive layer ( 140 . 240 . 340 . 440 ) generated. The at least one section thus typically forms a magneto-sensitive section of the fiber-optic sensor. The galvanic generation allows a simple variation of the layer thickness, the layer composition, for example the nickel content of nickel-iron alloys, and a simple structuring of the magnetostrictive layer in the direction of the fiber axis of the optically conductive fiber core. The layer thickness can easily be adjusted over the length of the galvanic process and / or the electrical voltage in wide ranges of about 2 .mu.m to 200 .mu.m, typically from 5 .mu.m to 50 .mu.m.

According to one embodiment, in a subsequent step 1500 generates an integrated coil. For this purpose, an insulating layer, for example a polymer layer, is typically first produced on the magnetostrictive layer. In this case, the insulating layer is typically produced flush with the coating of the sections of the fiber-optic sensor which adjoin the magnetosensitive sections. Thereafter, a further electrically conductive layer, for example in a sputtering process, is generated on the fiber-optic sensor. Subsequently, the coil turns are generated in the at least one magneto-sensitive section. This can be done by selective etching, laser ablation or medium FIB (Focused Ion Beam). Thereby, an integrally formed fiber optic sensor with integrated coil can be provided.

10 illustrates steps of a procedure 2000 for validating a fiber optic sensor according to an embodiment. In one step 2100 For example, the fiber-optic sensor is embedded in a test specimen in such a way that at least part of a magnetostrictive layer of the fiber optic sensor is located in the specimen. The specimen may be a machine, a machine part, a component or a building. Typically, the specimen and the embedded part of the fiber optic sensor form a solid composite. For example, the fiber optic sensor can be embedded in a carbon fiber reinforced plastic or a glass fiber reinforced plastic, but also in a concrete. The step of embedding can be done for example by lamination, gluing or pouring.

In one step 2200 a first signal of the fiber optic sensor is determined. The first signal may be a light signal backscattered or transmitted by the fiber optic sensor. Typically, the first signal is a measure of a transmission characteristic of the fiber optic sensor. For example, the transmission characteristic may be a proportion of a wavelength of the light signal backscattered by the fiber optic sensor.

In one step 2300 the magnetic field exposure of the magnetostrictive layer is changed. This can be done by switching on, generating or changing a magnetic field. In one step 2400 a second signal of the fiber optic sensor is determined during the changed magnetic field exposure of the magnetostrictive layer. The second signal also typically provides a measure of the transmission characteristic of the fiber optic sensor.

In one step 2500 an embedding state of the fiber optic sensor is determined in the specimen, for example, an adhesive state. The step 2500 includes comparing the first signal and the second signal. Typically, this involves determining a change in a transmission characteristic of the fiber optic sensor. Depending on the sensor type, the first and the second signal may correspond to a backscattered and / or transmitted light signal. If the fiber optic sensor is a fiber Bragg sensor, by comparing the signals, for example, a shift of a Bragg wavelength can be determined. As related to 6 has been explained, can be deduced on the determined shift of the Bragg wavelength in case of changing magnetic field exposure on the embedding state, such as the adhesion state of the fiber optic sensor.

Accordingly, in one step 2600 the fiber optic sensor can be calibrated so that in subsequent measurements in step 2700 calibrated can be performed. In step 2700 Thus, a measurement of a length of the specimen and / or an elongation of the specimen, in which a modified embedding state of the fiber-optic sensor has been corrected, can take place. This allows a simple and reliable monitoring of the specimen with the fiber optic sensor even over long periods.

The present invention has been explained with reference to exemplary embodiments. These embodiments should by no means be construed as limiting the present invention.

Claims (20)

Fiber optic sensor ( 100 . 200 . 300 . 400 . 500 ), comprising: - an optically conductive fiber core ( 110 . 210 . 310 . 410 ); An electrically conductive layer ( 140 . 240 . 340 . 440 ), the optically conductive fiber core in at least one section ( 455 . 555 ) surrounds; and - one on the electrically conductive layer ( 140 . 240 . 340 . 440 ) electroplated magnetostrictive layer ( 150 . 250 . 350 . 450 ). Fiber optic sensor ( 100 . 200 . 300 . 400 . 500 ) according to claim 1, wherein the magnetostrictive layer ( 150 . 250 . 350 . 450 ) comprises a nickel-iron alloy, a nickel-cobalt alloy, a nickel-iron-cobalt alloy, or an iron-cobalt alloy. Fiber optic sensor ( 100 . 200 . 300 . 400 . 500 ) according to claim 2, wherein the nickel content of the nickel-iron alloy ranges from about 10% to about 90%, more typically in a range from about 20% to about 70%, more typically in a range from about 25% to about 35%. lies. Fiber optic sensor ( 100 . 200 . 300 . 400 . 500 ) according to one of the preceding claims, wherein the magnetostrictive layer ( 150 . 250 . 350 . 450 ) has a layer thickness of from about 2 μm to about 200 μm, more typically from about 4 μm to about 100 μm, more typically from about 5 μm to about 50 μm. Fiber optic sensor ( 100 . 200 . 300 . 400 . 500 ) according to one of the preceding claims, further comprising a fiber cladding ( 120 . 320 . 420 ) and a primer layer ( 130 . 230 . 330 ), wherein the fiber cladding ( 120 . 320 . 420 ) between the optically conductive fiber core ( 110 . 210 . 310 . 410 ) and the magnetostrictive layer ( 150 . 250 . 350 . 450 ), and wherein the adhesion promoter layer ( 130 . 230 . 330 ) between the electrically conductive layer ( 140 . 240 . 340 . 440 ) and the fiber cladding ( 120 . 320 . 420 ) is arranged. Fiber optic sensor ( 100 . 200 . 300 . 400 . 500 ) according to one of claims 1 to 4, further comprising a primer layer ( 130 . 230 . 330 ) between the electrically conductive layer ( 140 . 240 . 340 . 440 ) and the optically conductive fiber core ( 210 ) is arranged. Fiber optic sensor ( 100 . 200 . 300 . 400 . 500 ) according to one of the preceding claims, further comprising an integrated coil ( 480 ), wherein the fiber optic sensor ( 100 . 200 . 300 . 400 . 500 ) and the integrated coil ( 480 ) are integrally formed. Fiber optic sensor ( 100 . 200 . 300 . 400 . 500 ) according to one of the preceding claims, wherein the optically conductive fiber core ( 110 . 210 . 310 . 410 ) in the at least one section ( 555 ) a fiber Bragg grating ( 550 ) having. Method for producing a fiber optic sensor ( 100 . 200 . 300 . 400 . 500 ), comprising: providing an optical fiber comprising at least one optically conductive fiber core ( 110 . 210 . 310 . 410 ); Application of an electrically conductive layer ( 140 . 240 . 340 . 440 ), so that the optically conductive fiber core ( 110 . 210 . 310 . 410 ) at least in one section ( 455 . 555 ) of the electrically conductive layer ( 140 . 240 . 340 . 440 ) is surrounded; and - galvanically generating a magnetostrictive layer ( 150 . 250 . 350 . 450 ) on the electrically conductive layer ( 140 . 240 . 340 . 440 ). Method according to claim 9, further comprising applying a primer layer ( 130 . 230 . 330 ) before applying the electrically conductive layer ( 140 . 240 . 340 . 440 ). Method according to claim 9 or 10, further comprising applying a further electrically conductive layer to produce an integrated coil ( 480 ) after electroplating the magnetostrictive layer ( 150 . 250 . 350 . 450 ). Method according to one of claims 9 to 11, wherein the application of the electrically conductive layer ( 140 . 240 . 340 . 440 ) and / or the application of the primer layer ( 130 . 230 . 330 ) and / or the application of the further electrically conductive layer comprises a sputtering process. Measuring system ( 600 . 6001 ) for the validation of a sample in a test specimen ( 700 ) embedded fiber optic sensor ( 100 . 200 . 300 . 400 . 500 ) with a magnetostrictive layer ( 150 . 250 . 350 . 450 ), comprising: - one with the fiber optic sensor ( 100 . 200 . 300 . 400 . 500 ) coupled light source ( 610 ) for generating a light signal ( 611 ); - a switchable magnetic field source ( 480 . 680 ), which is set up, at least the magnetostrictive layer ( 150 . 250 . 350 . 450 ) subject to a magnetic field; At least one with the fiber optic sensor ( 100 . 200 . 300 . 400 . 500 ) coupled detector ( 630 . 640 ); and - an evaluation unit ( 650 ) arranged to change a transmission characteristic of the fiber optic sensor ( 100 . 200 . 300 . 400 . 500 ) for the light signal ( 611 ) to detect when changing the magnetic field and from an embedding state of the fiber optic sensor ( 100 . 200 . 300 . 400 . 500 ) in the test piece ( 700 ). Measuring system ( 600 . 6001 ) according to claim 13, wherein said transmission characteristic comprises a portion of one of said fiber optic sensor ( 100 . 200 . 300 . 400 . 500 ) backscattered wavelength of the light signal ( 611 ). Measuring system ( 600 . 6001 ) according to claim 13 or 14, wherein the fiber optic sensor ( 100 . 200 . 300 . 400 . 500 ) an optically conductive fiber core ( 110 . 210 . 310 . 410 ), and wherein the switchable magnetic field source ( 480 ) between the optically conductive fiber core ( 110 . 210 . 310 . 410 ) and the specimen ( 700 ) is arranged. Measuring system ( 600 . 6001 ) according to one of claims 13 to 15, wherein the fiber optic sensor ( 100 . 200 . 300 . 400 . 500 ) is a fiber Bragg sensor, a Fabry-Perot sensor, a Raman sensor, a Brillouin sensor or a Rayleigh sensor. Method for validating a fiber optic sensor ( 100 . 200 . 300 . 400 . 500 ) with a magnetostrictive layer ( 150 . 250 . 350 . 450 ), comprising: embedding the fiber optic sensor ( 100 . 200 . 300 . 400 . 500 ) in a test specimen ( 700 ), so that at least a part of the magnetostrictive layer ( 150 . 250 . 350 . 450 ) in the test piece ( 700 ) is located; Determining a first signal of the fiber-optic sensor ( 100 . 200 . 300 . 400 . 500 ); Changing a magnetic field exposure of the magnetostrictive layer ( 150 . 250 . 350 . 450 ); Determining a second signal of the fiber optic sensor ( 100 . 200 . 300 . 400 . 500 ) during the changed magnetic field exposure; and determining an embedding state of the fiber optic sensor ( 100 . 200 . 300 . 400 . 500 ) in the test piece ( 700 )), comprising comparing the first signal and the second signal. The method of claim 17, further comprising: calibrating the fiber optic sensor 100 . 200 . 300 . 400 . 500 ). A method according to claim 17 or 18, wherein the embedding comprises a process of lamination and / or a process of sticking and / or a process of pouring. Method according to one of claims 17 to 19, further comprising: measuring a length of the test specimen ( 700 ); Measurement of an elongation of the test specimen ( 700 ); Determination of the bond between the fiber optic sensor ( 100 . 200 . 300 . 400 . 500 ) and the specimen ( 700 ); and / or - determining a change in a transmission characteristic of the fiber optic sensor.

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