CN116067298A

CN116067298A - Optical fiber strain sensor structure

Info

Publication number: CN116067298A
Application number: CN202310354247.2A
Authority: CN
Inventors: 王纪强; 朱梦娇; 刘真梅; 赵福军; 赵林; 侯墨语; 李振
Original assignee: Qilu University of Technology; Laser Institute of Shandong Academy of Science
Current assignee: Qilu University of Technology; Laser Institute of Shandong Academy of Science
Priority date: 2023-04-06
Filing date: 2023-04-06
Publication date: 2023-05-05
Anticipated expiration: 2043-04-06
Also published as: CN116067298B

Abstract

The application relates to the technical field of grating sensors and provides an optical fiber strain sensor structure, which comprises a substrate, wherein the substrate comprises a first surface in contact with the surface of an object to be measured, and a concave area, and the concave area comprises a concave surface on the same side as the first surface; the concave area is provided with a first strip-shaped hole; the first compensation sheet is provided with a first groove facing the concave surface, the second compensation sheet is provided with a second groove facing the concave surface, the first groove and the second groove extend along a first direction, and at least part of the first groove and the second groove are respectively overlapped with the first band-shaped hole; the fiber grating sequentially penetrates through the first groove and the second groove along the first direction, and the grating is arranged between the first groove and the second groove; the adhesive passes through the two first strip-shaped holes to fix the optical fibers in the first groove and the second groove respectively; the coefficient of thermal expansion of the substrate is less than the coefficient of thermal expansion of the compensator. According to the method and the device, the interference of temperature to the optical fiber strain sensor can be eliminated, and the measurement accuracy is improved.

Description

Optical fiber strain sensor structure

Technical Field

The application relates to the technical field of grating sensors, in particular to an optical fiber strain sensor structure.

Background

The fiber bragg grating sensor has the advantages of small volume, light weight, corrosion resistance, electromagnetic interference resistance, low transmission loss, convenience in multiplexing and networking and the like, and is widely applied to various fields. The fiber bragg grating sensor is affected by strain and temperature change simultaneously in the use process, so that both factors are considered simultaneously in calculation and are analyzed respectively, for example, when the fiber bragg grating is used for strain measurement, the fiber bragg grating wavelength is sensitive to temperature and strain simultaneously, namely, the temperature and the strain simultaneously cause the fiber bragg grating coupling wavelength to move, so that the temperature and the strain cannot be distinguished by measuring the fiber bragg grating coupling wavelength movement, namely, the temperature strain and the strain parameters interfere with each other, and therefore, the grating center wavelength change caused by the strain effect cannot be measured accurately. How to eliminate the influence of external temperature on the fiber grating strain sensor, thereby improving the measurement accuracy is a problem to be solved.

At present, a temperature compensation method is mainly adopted to eliminate the influence of external temperature on the fiber bragg grating strain sensor. Specifically, the temperature compensation method is to additionally add a temperature compensation grating on the fiber bragg grating strain sensor for strain measurement. Although the method can solve the influence of the external temperature on the fiber grating sensor to a certain extent, the method has the defects that for example, a temperature compensation grating added by adopting a temperature compensation method can lead to the problems of complex overall structure, complex demodulation, large measurement error, larger volume of the sensor and the like.

In view of the foregoing, there is a need for a fiber grating strain sensor that can automatically compensate for the effects of ambient temperature on strain measurements.

Disclosure of Invention

The application provides an optical fiber strain sensor structure, which can solve the problem that the strain sensor is influenced by the external temperature and the grating measurement accuracy is influenced.

The application provides an optical fiber strain sensor structure, comprising:

the substrate comprises a first surface which is contacted with the surface of the object to be measured, and the middle part of the first surface is recessed in the direction away from the object to be measured, and a recessed area is formed and comprises a recessed surface on the same side as the first surface;

the concave area is provided with two first strip-shaped holes which are arranged at intervals along the first direction;

the compensating plates comprise a first compensating plate and a second compensating plate, and the first compensating plate and the second compensating plate are respectively arranged on the concave surface and are distributed at two ends of the strain measuring area at intervals along the first direction;

the substrate and the compensation sheet form a strain measurement area;

the first compensation sheet is provided with a first groove facing the concave surface, the second compensation sheet is provided with a second groove facing the concave surface, and the first groove and the second groove extend along a first direction and are coaxially arranged; one of the first strip-shaped holes at least partially overlaps the first groove, and the other first strip-shaped hole at least partially overlaps the second groove;

the optical fiber grating sequentially penetrates through the first groove and the second groove along the first direction, and the optical fiber grating is arranged between the first groove and the second groove;

the adhesive passes through the two first strip-shaped holes to fix the optical fibers in the first groove and the second groove respectively;

the thermal expansion coefficient of the substrate is smaller than that of the compensation sheet, so that when the wavelength of the fiber grating shifts from the temperature change, the strain measurement area can perform temperature compensation on the wavelength change of the fiber grating.

In one embodiment, the adhesive is glass solder or epoxy, and the optical fiber is fixed to the first groove and the second groove by spot welding with the glass solder, or the optical fiber is fixed to the first groove and the second groove by bonding with the epoxy.

In one manner of implementation, the optical fiber strain sensor structure further comprises two protective sleeves; the substrate further comprises: two lugs, each lug is provided with a groove or a notch arranged along the first direction; wherein,,

the two lugs are respectively distributed at two ends of the concave area;

the protection sleeve extends along the first direction and is arranged in the groove or the notch, the two protection sleeves are coaxial with the first groove and the second groove, and the fiber bragg grating penetrates through the protection sleeve of the two lugs.

In one manner of implementation, the optical fiber strain sensor structure further comprises a fixing member; each lug is provided with two limiting holes; wherein,,

the two limiting holes are respectively arranged on two sides of the groove or the notch, the two limiting holes are connected through the fixing piece, and the fixing piece enables the groove or the notch to be folded inwards so as to clamp the protection sleeve.

In one way of implementation, each tab is further provided with two relief portions;

the two relieving parts are distributed on two sides of the fiber bragg grating;

each relieving part comprises a hollowed-out hole and a reed structure positioned in the hollowed-out hole;

the reed structure comprises a first reed connecting piece, a second reed connecting piece and an S-shaped reed, wherein one end of the first reed connecting piece is connected with the inner wall of one end of the hollowed hole, the other end of the first reed connecting piece is connected with the first free end of the S-shaped reed, one end of the second reed connecting piece is connected with the inner wall of the other end of the hollowed hole, and the other end of the second reed connecting piece is connected with the second free end of the S-shaped reed;

the reed structure is used for being attached to the surface of an object to be detected and relieving deformation of two ends of the substrate.

In one mode of implementation, two second strip-shaped holes are formed at two ends of the concave area along the first direction;

each second strip-shaped hole extends along a second direction, and the second direction is perpendicular to the first direction;

the two second band-shaped apertures are used to transfer the deformation of the strain measurement region to the grating through the compensator.

In one implementation manner, the first compensation plate includes two first sliding grooves extending along the first direction and distributed on two sides of the first groove; the second compensation sheet comprises two second sliding grooves which extend along the first direction and are distributed on two sides of the second groove; the two first sliding grooves and the two second sliding grooves are coaxially arranged in one-to-one correspondence;

the substrate also comprises two protection blocks, each protection block is arranged corresponding to one first chute and one second chute which are coaxially arranged, and the protection blocks are positioned in the orthographic projection area of the first chute and the second chute which are coaxially arranged in the strain measuring area;

each protection block is embedded into a corresponding first chute and a second chute, so that the two protection blocks protect the covered optical fiber area;

the distance between the two ends of the first sliding groove and the second sliding groove, which are mutually far away, is larger than the length of the protection block along the first direction.

In one mode, a first mark point is arranged in the first groove, and the first mark point is positioned at the end part of the first groove, which is close to the second compensation sheet;

a second mark point is arranged in the second groove and is positioned at the end part of the second groove, which is close to the first compensation sheet;

the grating of the fiber grating is provided with a marking color for positioning the grating position;

the first mark point and the second mark point are fixed points of the optical fiber, so that the grating of the optical fiber grating is arranged between the first groove and the second groove.

In one manner of implementation, the compensation sheet includes a second surface for contacting a surface of an object to be measured;

the first surface and the second surface lie in the same plane.

In one mode of implementation, the substrate is made of copper material; the compensation sheet is made of aluminum materials.

Advantageous effects

The application relates to an optical fiber strain sensor structure, which utilizes the difference of thermal expansion coefficients of a substrate and a compensation sheet to form a strain measurement area. The strain measurement area can compress and stretch the fiber grating along with temperature change, effectively compensates wavelength change of the fiber grating caused by thermo-optical effect, and realizes compensation of fiber grating wavelength movement caused by sensitivity of the fiber grating to temperature based on the fiber grating when external temperature changes, namely, when temperature changes, the strain effect of the grating caused by temperature change is mutually counteracted by the composite effect of the substrate and the compensation sheet on the compression and the stretching of the grating, and the grating wavelength is kept unchanged, so that interference of external temperature to the fiber strain sensor is eliminated, and measurement accuracy is improved.

Drawings

In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings that are needed in the description of the embodiments or the prior art will be briefly described, and it is obvious that the drawings in the description below are some embodiments of the present invention, and other drawings can be obtained according to the drawings without inventive effort for a person skilled in the art.

FIG. 1 is a top view of a fiber optic strain sensor structure;

FIG. 2 is a schematic diagram of a fiber grating of a fiber strain sensor structure;

FIG. 3 is a schematic illustration of a substrate of a fiber optic strain sensor structure;

FIG. 4 is a cross-sectional view of the strain gage region and compensator of FIG. 1;

FIG. 5 is a schematic diagram of a compensator of an optical fiber strain sensor structure;

fig. 6 is a schematic diagram of the working principle of an optical fiber strain sensor structure.

Reference numerals:

1-a substrate; 11-a first surface; 12-a recessed region; 121-a first band-shaped aperture; 131-a first straight slot; 132-a second straight slot; 133-a third straight slot; 134-fourth straight slot; 135-a fifth straight slot; 14-ear pieces; 141-a limiting hole; 142-fixing piece; 143-a relief portion; 1431-a hollowed hole; 1432-a first reed connector; 1433-a second reed connector; 1434-S spring; 144-a second band-shaped aperture; 15-protecting the sleeve; 16-slots or indentations; 17-a protection block;

2-compensating sheets; 21-a first compensation sheet; 211-a first groove; 2111-a first marker point; 212-a first chute; 22-a second compensation sheet; 221-a second groove; 2211-a second mark point; 222-a second chute; 23-a second surface;

3-fiber grating; 31-grating.

Detailed Description

The technical solutions of the present invention will be clearly and completely described in connection with the embodiments, and it is apparent that the described embodiments are some embodiments of the present invention, but not all embodiments. All other embodiments, which can be made by those skilled in the art based on the embodiments of the invention without making any inventive effort, are intended to be within the scope of the invention.

Typically, the fiber grating wavelength is sensitive to both temperature and strain, i.e., the temperature and strain simultaneously cause the fiber grating coupling wavelength to shift such that the temperature and strain cannot be distinguished by measuring the fiber grating coupling wavelength shift. Therefore, the problem of cross sensitivity is solved, and the realization of differentiated measurement of temperature and stress is a precondition for the practical use of the sensor.

Therefore, the change of temperature can cause the change of the grid distance and the refractive index of the fiber grating, so that the reflection spectrum and the transmission spectrum of the fiber grating are changed, when the incident light is reflected back through the Bragg grating, the center wavelength of the reflected light drifts due to the modulation of the temperature, and the drift amount has a linear relation with the temperature and the strain. The temperature compensation is used for eliminating the wavelength shift of the fiber bragg grating coupling caused by the temperature, so that only the wavelength change caused by the strain can be reflected, that is, the temperature interference can be eliminated by the temperature compensation, the influence of the strain on the fiber bragg grating can be directly obtained, the calculated amount is reduced, and the strain measurement accuracy is improved. As shown in fig. 1 to 3, an embodiment of the present application provides an optical fiber strain sensor structure, including: a substrate 1, a compensation sheet 2, a fiber grating 3 and an adhesive. Wherein:

the substrate 1 includes a first surface 11 in contact with the surface of the object to be measured, and a concave region 12 formed in a central portion of the first surface 11 to be recessed in a direction away from the object to be measured, the concave region 12 including a concave surface on the same side as the first surface 11.

The base sheet 1 and the compensation sheet 2 may be made of materials having different coefficients of expansion, wherein the coefficient of thermal expansion of the base sheet 1 is smaller than that of the compensation sheet 2. Illustratively, the substrate 1 is made of a brass material, the compensation plate 2 is made of an aluminum material, and the fiber grating 3 is a quartz fiber. The compensation plate 2 is located in the projection area of the recessed area 12 and is arranged on the recessed surface, and the compensation plate 2 comprises a first compensation plate 21 and a second compensation plate 22. The first and second compensating

plates

21 and 22 are disposed on the concave surface and distributed at both ends of the concave region 12 in the first direction.

The compensation plate 2 and the substrate 1 form a strain measurement area.

Wherein the first and second compensating

plates

21 and 22 may have the same shape and be mirror-image disposed in the recessed area 12.

The compensation plate 2 further comprises a second surface 23 for contacting the surface of the object to be measured. With the first and

second compensator

21, 22 disposed in the recessed region 12, the second surface 23 of the compensator 2 and the first surface 11 of the substrate 1 are in the same plane. In some embodiments, the first compensation sheet 21 and the second compensation sheet 22 may be fixed on the substrate 1 by welding, and the first compensation sheet 21 and the second compensation sheet 22 are spaced apart by a predetermined distance, wherein the predetermined distance may be selected according to the length of the grating, which is not limited in this application. Specifically, through grooves are formed in corresponding positions of the substrate 1, which are respectively connected with the first compensation sheet 21 and the second compensation sheet 22, and at least one through groove is formed. Preferably, the through grooves are straight-mouth grooves, and the number is four, that is, the straight-mouth grooves of the substrate 1 corresponding to the first compensation sheet 21 are the first straight-mouth groove 131 and the second straight-mouth groove 132, respectively; the straight grooves corresponding to the second compensating plate 22 on the substrate 1 are a third straight groove 133 and a fourth straight groove 134, respectively. When the substrate 1 is assembled with the first compensating plate 21 and the second compensating plate 22, respectively, the first compensating plate 21 may be welded through the first straight slot 131 and the second straight slot 132 using a welding device so as to weld the first compensating plate 21 on the substrate 1, thereby achieving the fixation of the first compensating plate 21 and the substrate 1. Likewise, the second compensating plate 22 is welded to the substrate 1 through the third and fourth

straight slits

133 and 134 using a welding apparatus, and the second compensating plate 22 is fixed to the substrate 1. The welding is only one fixing method of the base sheet 1 and the first and second compensating

sheets

21 and 22, and the compensating sheet 2 may be fixed to the base sheet 1 by crimping or hinge connection at high temperature and high pressure, and the fixing method is not limited in this application.

By fixing the substrate 1 to the first compensation plate 21 and the second compensation plate 22, the first compensation plate 21, the second compensation plate 22 and the substrate 1 can form a stable whole, and the wavelength fluctuation of the grating 31 caused by poor stability of the connection between the first compensation plate 21, the second compensation plate 22 and the substrate 1 can be avoided.

In some embodiments, the first compensator 21 is provided with a first groove 211 facing the first surface 11, the second compensator 22 is provided with a second groove 221 facing the first surface 11, and the first groove 211 and the second groove 221 extend in a first direction and are coaxially arranged. The first groove 211 and the second groove 221 form a space for accommodating the fiber grating 3.

The recessed area 12 has two first strip-shaped holes 121 arranged along the first direction, the two first strip-shaped holes 121 are arranged at intervals, and the two first strip-shaped holes 121 may be respectively orthographic projected on the first groove 211 and the second groove 221, or may be partially projected on the first groove 211 and the second groove 221.

When the compensation plate 2 is assembled in the concave region of the substrate 1, the two first strip holes 121 can be partially overlapped with the corresponding first grooves 211 and second grooves 221, respectively, and the first strip holes 121 become windows of the bare fiber grating 3. In this case, in the case where the optical fiber grating 3 is disposed through the first groove 211, the recessed region 12, and the second groove 221, the first mark point 2111 and the second mark point 2211 in the first groove 211 and the second groove 221 located at the overlapping positions are exposed in the window.

The adhesive passes through the first strip-shaped hole 121 to fix the optical fiber of the fiber grating 3 at the first mark point 2111 and the second mark point 2211 corresponding to the first groove 211 and the second groove 221.

Wherein the adhesive is glass solder or epoxy, and the optical fiber is fixed to the first groove 211 and the second groove 221 by spot welding of glass solder or bonding of epoxy. So that the fiber grating 3, the compensation plate 2 and the substrate 1 form a unitary structure. That is, when the external temperature changes, the composite effect of the compression and the extension of the grating 31 by the substrate 1 and the compensation sheet 2 and the strain effect of the grating 31 caused by the temperature change cancel each other, and the wavelength of the grating 31 remains unchanged.

As shown in fig. 2, the middle part of the fiber bragg grating 3 is provided with a grating 31, and when the fiber bragg grating 3 sequentially passes through the first groove 211, the concave region 12 and the second groove 221 along the first direction and is fixed in the first groove 211 and the second groove 221, the grating 31 is placed in the center of the concave region 12. Specifically, the grating 31 may be disposed between the first groove 211 and the second groove 221.

The fiber grating 3 is fixedly connected with the first groove 211 and the second groove 221. In this embodiment, the difference in thermal expansion coefficients of the materials is used to form the temperature compensation of the substrate 1 and the compensation sheet 2, and the fiber grating 3 is fixed in the first groove 211, the concave region 12 and the second groove 221 to form an integral structure, which makes the fiber strain sensor structure maintain the original wavelength of the grating 31 as much as possible in the environment of external temperature change. Specifically, when the external temperature is applied, the thermo-optic effect causes a change in the effective refractive index of the grating 31, and the period of the grating 31 also changes due to the thermal expansion effect, and these changes eventually cause a shift in the wavelength of the grating 31. Because the thermal expansion coefficient of the substrate 1 is smaller than that of the compensation sheet 2, the deformation amount of the substrate 1 is small, the deformation amount of the compensation sheet 2 is large, the deformation of the compensation sheet 2 can cause the change of the distance between the first compensation sheet 21 and the second compensation sheet 22, the change of the distance can offset the change of the wavelength of the grating 31, the wavelength of the grating 31 is effectively compensated for by temperature, the deformation of the fiber grating 3 is reduced or eliminated, and the cross interference of the temperature is eliminated.

As shown in fig. 1 and 2, in one embodiment, the fiber optic strain sensor structure further comprises two protective sleeves 15; the substrate 1 further comprises two tabs 14 distributed in the first direction at both ends of the recessed area 12, each tab 14 being provided with a groove or notch 16 arranged in the first direction. The two lugs 14 are respectively distributed at two ends of the concave area 12, the protection sleeve 15 is arranged in the groove or notch 16 along the extending direction, the protection sleeve 15 is coaxial with the first groove 211 and the second groove 221, and the fiber grating 3 is arranged in the groove or notch 16 and the protection sleeve 15 in a penetrating way.

Wherein the protective sleeve 15 may be embedded in the tab 14 such that the protective sleeve 15 is coaxial with the first recess 211 and the second recess 221. The protective sleeve 15 can protect the optical fiber portion of the fiber grating 3 from damage caused by contact of the optical fiber with the tab 14. Preferably, the protective sleeve 15 may be a metal sleeve, a teflon sleeve, a glass fiber protective tube, or the like.

It should be noted that the protection sleeve 15 may be embedded in the tab 14, so as to realize the coaxial alignment of the protection sleeve 15, the first groove 211 and the second groove 221. The fiber grating 3 can be better penetrated in the protective sleeve 15 by the structure, and grooves can be formed on the lug 14 along the first direction or part of the lug 14 can be processed into a strip-shaped notch. Thus, the grooves or notches 16 can form channels through which the fiber bragg gratings 3 penetrate, so that the fiber bragg gratings 3 can penetrate in the first direction on the substrate 1.

The fiber optic strain sensor structure further includes a securing member 142; two limiting holes 141 are formed in each lug 14. The two limiting holes 141 are respectively arranged at two sides of the groove or notch 16, and the two limiting holes 141 are connected through the fixing piece 142, so that the fixing piece 142 can enable the wall of the groove or notch 16 to move relatively, namely to retract inwards, so that the protection sleeve 15 is clamped in the through groove.

It should be noted that, the two ends of the fixing member 142 are fixed at the positions of the limiting holes 141 on the outer edges of the opposite side walls of the slot or notch 16, and the fixing manner of the two ends of the fixing member 142 may be welding, and it should be noted that, if the slot or notch 16 is a slot, one fixing member 142 is provided at the open end of the slot to be welded with the opposite limiting holes 141, and if the slot or notch 16 is a notch, one fixing member 142 may be provided in the thickness direction of the tab 14 to pass through the limiting holes 141 circumferentially to wrap the protective sleeve 15, or two fixing members 142 may be provided on the opposite surfaces of the tab 14 in the thickness direction to be welded with the two limiting holes 141. The protective sleeve 15 is prevented from swinging in the depth direction of the groove or notch 16 by the fixing member 142. Thereby securing the protective sleeve 15 within the slot or notch 16. The fixing member 142 may be an iron wire welded to the outer edges of the opposite side walls of the slot or indentation 16 using an epoxy or glass solder. Two limiting holes 141 on the outer edges of the opposite side walls of the groove or notch 16 are in one group, multiple groups can be arranged on the lug 14 according to the needs, each group of limiting holes 141 is correspondingly provided with a fixing piece 142, and the multiple groups of limiting holes 141 are distributed in sequence along the length direction of the groove or notch 16.

In addition, through grooves for fixing the lugs 14 on the surface of the object to be tested are further formed in the lugs 14, and the number of the through grooves in each lug 14 is at least one. To ensure stability of the tabs 14, the number of through slots in each tab 14 is preferably two, and the through slots may be straight slots. That is, two fifth straight slits 135 are provided on each tab 14. The positions of the two fifth straight slits 135 may be set as needed, and the positions of the fifth straight slits 135 are not limited in this application. Illustratively, two fifth through slots 135 on each tab 14 are provided in the second direction.

As shown in fig. 1, in one embodiment, each tab 14 is further provided with two relief portions 143, the two relief portions 143 being distributed on both sides of the fiber grating 3.

Each relief portion 143 includes a hollow hole 1431 and a reed structure disposed in the hollow hole 1431. The reed structure comprises a first reed connecting piece 1432, a second reed connecting piece 1433 and an S-shaped reed 1434, wherein one end of the first reed connecting piece 1432 is connected with the inner wall of one end of the hollow hole 1431, the other end of the first reed connecting piece 1432 is connected with the first free end of the S-shaped reed 1434, one end of the second reed connecting piece 1433 is connected with the inner wall of the other end of the hollow hole 1431, and the other end of the second reed connecting piece 1433 is connected with the second free end of the S-shaped reed 1434. The reed structure is used for being attached to the surface of an object to be detected and relieving deformation of two ends of the substrate 1.

When the substrate 1 is deformed by the influence of the external temperature, the substrate 1 is deformed by the deformation. When the deformation amount is released, the alleviating portion 143 is used as: on the one hand, the hollowed-out structure of the hollowed-out hole 1431 can reduce the deformation of the lug 14; on the other hand, when the tab 14 is deformed, most of the deformation amount acts on the relief portion 143, and then the first and

second reed connectors

1432 and 1433 of the relief portion 143 absorb the deformation amount and transmit the deformation amount to the S-shaped reed 1434, so that the deformation amount deforms the S-shaped reed 1434. The S-shaped reed 1434 digests the deformation amount by utilizing deformation, thereby reducing the influence of deformation at two ends of the sensor on the service life of the sensor.

As shown in fig. 1, in one embodiment, two second band-shaped apertures 144 are provided at both ends of the recessed area 12 in the first direction. Each of the second strip-shaped holes 144 extends in a second direction, which is perpendicular to the first direction. Under the condition that the concave area 12 is influenced by external temperature to deform, the strain sensitivity of the optical fiber strain sensor can be improved, when the load is applied to the two ends of the substrate 1, the strain of an object can be effectively transferred to the grating 31 in the middle of the two compensating plates 2 through the structure, the strain of the grating 31 part is amplified, and the strain detection sensitivity of the optical fiber strain sensor is improved.

As shown in fig. 1, 3 and 4, in one embodiment, the first compensation plate 21 includes two first sliding grooves 212, and the two first sliding grooves 212 extend along the first direction and are distributed on two sides of the first groove 211. The second compensation plate 22 includes two second sliding grooves 222, the two second sliding grooves 222 extend along the first direction and are distributed on two sides of the second groove 221, and the two first sliding grooves 212 and the two second sliding grooves 222 are coaxially arranged in one-to-one correspondence.

The substrate 1 further comprises two protection blocks 17, and each protection block 17 is arranged corresponding to one first chute 212 and one second chute 222 which are coaxially arranged, and is positioned in the orthographic projection area of one first chute 212 and one second chute 222 which are coaxially arranged in the concave area 12.

Each protection block 17 is embedded in a corresponding one of the first sliding groove 212 and the second sliding groove 222, and the distance between the two ends of the first sliding groove 212 and the second sliding groove 222, which are far away from each other, is larger than the length of the protection block 17 along the first direction, that is, the length of the protection block 17 is larger than the distance between the first sliding groove 212 and the second sliding groove 222, so that the two protection blocks 17 completely protect the area of the optical fiber grating 3 covered by the protection block 17.

When the first compensation sheet 21, the second compensation sheet 22 and the concave area 12 are deformed under the influence of temperature and stress load, the first chute 212 and the second chute 222 are respectively in sliding connection with the protection block 17, so that on one hand, compensation of the deformation of the optical fiber grating 3 by the compensation sheet 2 is ensured, and on the other hand, the protection block 17 can protect the optical fiber grating 3 between the covered first compensation sheet 21 and the covered second compensation sheet 22.

As shown in fig. 1, 2 and 5, in one embodiment, a first marking point 2111 is provided in the first groove 211, the first marking point 2111 being located at an end of the first groove 211 near the second compensation plate 22. A second mark point 2211 is provided in the second groove 221, and the second mark point 2211 is located at an end of the second groove 221 near the first compensation plate 21. The grating 31 of the fiber grating 3 is provided with a marking color.

The first mark point 2111 and the second mark point 2211 are used as mark points for fixing the fiber bragg grating 3, and the distance between the first mark point 2111 and the second mark point 2211 and the fixing point of the fiber bragg grating 3 can be obtained for calculating the temperature compensation coefficient of the sensor.

It should be noted that, the first mark point 2111 and the second mark point 2211 are respectively located at positions where the two first strip-shaped holes 121 partially overlap with the corresponding first groove 211 and second groove 221, so that the first mark point 2111 and the second mark point 2211 can be respectively observed through the two first strip-shaped holes 121, so that when the fiber grating 3 is disposed through the first groove 211 and the second groove 221, the mark color of the grating 31 on the fiber grating 3 is used to locate the grating 31, and the mark color corresponds to the first mark point 2111 and the second mark point 2211, so that the position of the grating 31 is determined by the correspondence relationship between the first mark point 2111 and the second mark point 2211 and the mark color. Next, an adhesive may be injected into the first mark point 2111 and the second mark point 2211 through the two first strip holes 121, and the optical fiber is fixed at the first mark point 2111 and the second mark point 2211 by the adhesive, thereby fixing the optical fiber grating 3 to the compensation sheet 2. The first mark point 2111 and the second mark point 2211 may be grooves with smaller dimensions, so that when the adhesive is respectively dropped into the first mark point 2111 and the second mark point 2211, the grooves forming the first mark point 2111 and the second mark point 2211 can accommodate the adhesive, so that the adhesive is prevented from flowing outwards, the bonding position of the optical fiber is overlong and is not stuck, the position of the fixing point is inaccurate, and the temperature compensation coefficient is calculated inaccurately.

The working principle of the optical fiber strain sensor structure provided by the embodiment of the application is as follows:

the fiber optic strain sensor structure utilizes two different materials of low and high coefficients of thermal expansion to produce wavelength shift caused by thermo-optic effects compensated by differences in coefficients of thermal expansion. Specifically, when the external temperature changes, the lengths of the substrate and the compensation sheet are changed due to the physical characteristics of thermal expansion and cold contraction of the high thermal expansion coefficient material. The difference between the length change of the substrate and the compensation sheet is then transferred to the fiber grating. The difference in the variation amounts counteracts the wavelength drift amount of the fiber grating. Therefore, the temperature sensitivity coefficient of the fiber bragg grating can be reduced by selecting two different materials with low thermal expansion coefficient and high thermal expansion coefficient and corresponding structures.

In some embodiments, the low coefficient of thermal expansion material may be brass and the high coefficient of thermal expansion material may be aluminum, and accordingly, the base sheet 1 may be made of brass and the compensator sheet 2 may be made of aluminum, such that the base sheet 1 and compensator sheet 2 form a bi-metallic structure. Under the physical action of bimetal (brass and aluminum), the substrate 1 and the compensation sheet 2 have better insensitivity to temperature and can reflect strain change, so that when the temperature of the substrate 1 and the compensation sheet 2 is increased, the compression amount of the fiber bragg grating 3 and the tensile amount of the fiber bragg grating 3 can be offset, and the temperature self-compensation of the strain sensor is realized.

The working principle of the optical fiber strain sensor structure provided in the embodiment of the application is described in more detail below with reference to the accompanying drawings and formulas:

as shown in fig. 6, the fiber grating variation

The calculation formula of (2) is as follows:

（1）

wherein,,

for the thermal expansion coefficient of the substrate 1 +.>

The coefficient of thermal expansion of the compensation plate 2 +.>

For the length between the connection of the first compensation plate 21 to the substrate 1 and the connection of the second compensation plate 22 to the substrate 1->

Fixing the distance between the fiber grating for the first compensation plate 21 and the fiber grating 3 for the second compensation plate 22,/for the first compensation plate 21>

As the amount of change in the length of the substrate 1,

to compensate for the sheet length variation.

The two ends of the fiber grating 3 are respectively fixed on the first compensation sheet 21 and the second compensation sheet 22 by using an adhesive, when the external temperature changes, the wavelength change of the fiber grating 3 is composed of elastic strain caused by the thermo-optical effect and the thermal expansion of the structure, and the wave of the fiber grating 3Length variation

The calculation formula is as follows:

（2）

wherein,,

is the elasto-optic coefficient of the optical fiber, < >>

Is the thermo-optic coefficient of the optical fiber, < >>

Is the center wavelength of the fiber grating 3.

The wavelength shift of the fiber grating 3 is affected

And->

Influence of changes, but->

The magnitude is related to the stretching and compression of the grating 31, so that the red shift or blue shift of the fiber grating 3 can be compensated by the compressed or stretched grating distance, where red shift means an increase in wavelength and blue shift means a decrease in wavelength.

Ideally, it is assumed that thermal expansion of the substrate 1 and the compensation plate 2 can be transmitted to the fiber grating 3 without loss, and strain of the fiber grating 3 caused by temperature change

The calculation formula is as follows:

（3）

fiber bragg grating 3 temperature sensitivity coefficient

The calculation formula is as follows:

（4）

the temperature sensitivity coefficient of the bimetallic structure can be obtained by the formulas (2), (3) and (4)

The calculation formula is as follows:

（5）

as can be seen from equation (5), the thermal expansion coefficients and lengths of the base sheet 1 and the compensation sheet 2 affect the temperature sensitivity coefficient of the strain sensor. When the length of the substrate 1 is fixed from the distance between the compensating plates 2, i.e

And->

The temperature sensitivity coefficient of the strain sensor is related only to the difference in the thermal expansion coefficients of the bimetal. When the material is determined, the temperature sensitivity coefficient of the fiber bragg grating 3 is a constant related to the length of the material. Based on the theory, the strain sensor manufactured by adopting the fiber bragg grating 3 is guaranteed to have temperature insensitivity.

Because the substrate 1 is brass with low thermal expansion coefficient, the compensating plate 2 is metal aluminum with high thermal expansion coefficient, and the thermal expansion coefficients of the substrate 1 and the compensating plate 2 are respectively

，

. Will->

And->

The thermal expansion coefficients of brass and metal aluminum are respectively substituted, and the temperature sensitivity coefficient of the bimetal structure is +.>

And->

And->

The relation calculation formula of (2) is as follows: />

（6）

Wherein,,

the unit is->

。

When the external temperature rises, the bimetal structure is in a compressed state for the fiber grating 3 due to the physical characteristics of the metal material, and the fiber grating 3 is in an expanded and stretched state due to the influence of the thermo-optical effect. As can be seen in the combination of equation (6), in

And

when the ratio is about 6.71, the compression amount of the bimetal material and the stretching amount of the fiber grating 3 can be counteracted, and the temperature self-compensation of the strain sensor is realized.

As shown in fig. 6, the optical fiber strain sensor structure provided in the embodiment of the present application can realize sensitization, that is, amplification of strain sensitivity, in addition to the foregoing temperature compensation. The specific sensitization principle is as follows:

fixed point distance between strain sensor and object to be measured

Is larger than the fiber bragg grating 3 to be fixedPoint distance->

And the second band-shaped apertures 144 in combination with the compensator 2 may be effective to concentrate strain between the first compensator 21 and the second compensator 22. When the object to be measured is deformed, the deformation amount of the strain measurement area is +.>

Almost all of the light is concentrated on the fiber grating 3. When the strain of the object to be measured is +.>

The strain to which the fiber grating 3 is subjected may be approximately +.>

So that the strain sensitivity magnification of the strain sensor is about +.>

. Illustratively, assume ∈ ->

70 mm->

The strain sensitivity magnification of the strain sensor is about 7 times at 10 mm.

The foregoing examples merely illustrate specific embodiments of the invention, which are described in greater detail and are not to be construed as limiting the scope of the invention. It should be noted that it will be apparent to those skilled in the art that several variations and modifications can be made without departing from the spirit of the invention, which are all within the scope of the invention.

Claims

1. An optical fiber strain sensor structure, comprising:

the substrate comprises a first surface which is in contact with the surface of the object to be detected, and the middle part of the first surface is recessed in a direction away from the object to be detected, and a recessed area is formed, wherein the recessed area comprises a recessed surface on the same side as the first surface;

the compensating plates comprise a first compensating plate and a second compensating plate, and the first compensating plate and the second compensating plate are respectively arranged on the concave surface and are distributed at two ends of the concave surface at intervals along the first direction;

the substrate and the compensation sheet form a strain measurement area;

the first compensation sheet is provided with a first groove facing the concave surface, the second compensation sheet is provided with a second groove facing the concave surface, and the first groove and the second groove extend along the first direction and are coaxially arranged; one of the first strip-shaped holes at least partially overlaps with the first groove, and the other first strip-shaped hole at least partially overlaps with the second groove;

the optical fiber grating sequentially penetrates through the first groove and the second groove along the first direction, and the grating is arranged between the first groove and the second groove;

an adhesive for fixing the optical fiber in the first groove and the second groove through the two first band-shaped holes respectively;

the thermal expansion coefficient of the substrate is smaller than that of the compensation sheet, so that when the wavelength of the fiber grating shifts from temperature change, the strain measurement area can perform temperature compensation on the wavelength change of the fiber grating.

2. The optical fiber strain sensor structure of claim 1,

the adhesive is glass solder or epoxy resin, the optical fiber is fixed in the first groove and the second groove in a spot welding mode through the glass solder, or the optical fiber is fixed in the first groove and the second groove in an adhesive mode through the epoxy resin.

3. The fiber optic strain sensor structure of claim 2, further comprising two protective sleeves;

the substrate further comprises: two lugs, each of which is provided with a groove or a notch arranged along the first direction; wherein,,

the two lugs are respectively distributed at two ends of the concave area; the protection sleeves are arranged in the grooves or the notches in an extending mode along the first direction, the two protection sleeves are coaxial with the first grooves and the second grooves, and the fiber bragg gratings penetrate through the protection sleeves of the two lugs.

4. The fiber optic strain sensor structure of claim 3, further comprising a mount; two limiting holes are formed in each lug; wherein,,

5. The optical fiber strain sensor structure of claim 3,

each lug is also provided with two relieving parts;

the reed structure is used for being attached to the surface of the object to be detected and relieving deformation of the two ends of the substrate.

6. The optical fiber strain sensor structure of claim 5,

two ends of the concave area are provided with two second strip-shaped holes along the first direction;

each of the second strip-shaped holes extends in a second direction, and the second direction is perpendicular to the first direction;

the two second strip-shaped holes are used for transmitting deformation of the strain measurement area to the grating through the compensation sheet.

7. The optical fiber strain sensor structure of claim 1,

the first compensation sheet comprises two first sliding grooves, and the two first sliding grooves extend along the first direction and are distributed on two sides of the first groove; the second compensation sheet comprises two second sliding grooves, and the two second sliding grooves extend along the first direction and are distributed on two sides of the second groove; the two first sliding grooves and the two second sliding grooves are coaxially arranged in one-to-one correspondence;

the substrate also comprises two protection blocks, wherein each protection block is arranged corresponding to one first chute and one second chute which are coaxially arranged, and is positioned in the orthographic projection area of one first chute and one second chute which are coaxially arranged in the strain measurement area;

each protection block is embedded into one corresponding first chute and one corresponding second chute, so that the two protection blocks protect the covered optical fiber area;

and the distance between the two ends of the first sliding groove and the second sliding groove, which are mutually far away, is larger than the length of the protection block along the first direction.

8. The optical fiber strain sensor structure of claim 1,

a first mark point is arranged in the first groove and is positioned at the end part of the first groove, which is close to the second compensation sheet;

9. The optical fiber strain sensor structure of claim 1,

the compensation sheet comprises a second surface for contacting with the surface of the object to be measured;

the first surface and the second surface lie in the same plane.

10. The optical fiber strain sensor structure of any of claims 1-9, wherein the substrate is made of a copper material; the compensating sheet is made of aluminum materials.