A radiation-resistant fiber Bragg grating high-temperature strain sensor and its sensitivity adjustment method

Abstract

This invention discloses a radiation-resistant fiber Bragg grating high-temperature strain sensor, comprising a strain measurement fiber Bragg grating and a metal substrate. The metal substrate includes a central deformation section and two outer wings, which are symmetrically connected to both ends of the central deformation section along the fiber optic axis. Each outer wing includes a first rigid connection section, an outer deformation section, a second rigid connection section, and a rigid fixing section arranged sequentially along the fiber optic axis. The two rigid fixing sections are used to connect and fix the sensor to the object being measured. The strain measurement fiber Bragg grating is located on the central deformation section, and its two ends are respectively connected and fixed to the two first rigid connection sections one-to-one through fixing points. This radiation-resistant fiber Bragg grating high-temperature strain sensor can solve at least one of the problems encountered when applying it to nuclear power plants, such as radiation resistance, high temperature resistance, temperature-strain decoupling, and the inability to simultaneously achieve miniaturization and large range. This invention also discloses a sensitivity adjustment method for the above sensor.

Description

Technical Field

[0001] This invention relates to fiber Bragg grating high-temperature strain sensors, and more particularly to a radiation-resistant fiber Bragg grating high-temperature strain sensor and its sensitivity adjustment method. Background Technology

[0002] Nuclear power plants, as a crucial component of the modern energy supply system, play a significant role in promoting a low-carbon economy and sustainable development, alleviating energy shortages, and mitigating energy security risks. Nuclear power has become one of the most important energy sources for China's industrial development, and China has entered the ranks of the world's leading nuclear power technologies. On the other hand, serious accidents such as the Chernobyl, Three Mile Island, and Fukushima Daiichi nuclear disasters have caused enormous economic losses, casualties, and severe environmental damage, serving as a stark reminder of the importance of safe nuclear power use. Ensuring the safety of nuclear energy development hinges on preventing and effectively mitigating nuclear accidents; this is the most critical and indispensable primary task in the development of the nuclear power industry.

[0003] Fiber Bragg grating high-temperature strain sensors are optical sensors based on fiber Bragg gratings. They utilize the coupling shift characteristics of the grating resonant wavelength with temperature and strain to achieve accurate detection of strain parameters of the measured object under high-temperature conditions. They also have the inherent advantages of fiber optic sensors, such as being passive, resistant to electromagnetic interference, small in size, and capable of distributed monitoring. They are widely used in structural health monitoring and safety early warning in high-temperature and extreme industrial scenarios such as aerospace and petrochemical industries, and are one of the core sensing devices for strain detection in extreme environments.

[0004] However, the application of fiber Bragg grating high-temperature strain sensors in nuclear power plants still faces many challenges: 1. Conventional optical fiber materials and coatings are susceptible to damage from nuclear radiation, leading to optical power attenuation and sensing performance drift, making them unsuitable for extreme working conditions with high temperature and high radiation. 2. The cross-coupling effect between temperature and strain has not been effectively resolved, which can easily lead to distortion of measurement results; 3. Traditional substrate-based packaging structures achieve sensitivity adjustment by increasing the size of the metal substrate, which cannot meet the requirements of miniaturization and large-range strain measurement. Furthermore, the difference in thermal expansion coefficients between the metal substrate and the optical fiber can easily introduce additional thermal strain, further reducing monitoring accuracy. Summary of the Invention

[0005] To address the shortcomings of the prior art, this invention provides a radiation-resistant fiber Bragg grating high-temperature strain sensor and a sensitivity adjustment method to solve at least one of the problems it faces when applied in nuclear power plants, such as radiation resistance, high temperature resistance, temperature-strain decoupling, and the inability to simultaneously achieve miniaturization and large range.

[0006] The technical problem to be solved by the present invention is achieved through the following technical solution: A radiation-resistant fiber Bragg grating high-temperature strain sensor includes a strain measurement fiber Bragg grating and a metal substrate. The metal substrate has fiber grooves along the fiber axis, and the strain measurement fiber Bragg grating is disposed within the fiber grooves. The metal substrate includes a central deformation portion and two outer wings, which are symmetrically connected to both ends of the central deformation portion along the fiber axis. Each outer wing includes a first rigid connection portion, an outer deformation portion, a second rigid connection portion, and a rigid fixing portion arranged sequentially along the fiber axis. Two rigid fixing parts are used to connect and fix the object being measured; When subjected to axial stress, the two rigid fixing parts, the two first rigid connecting parts, and the two second rigid connecting parts do not produce axial deformation. The intermediate deformation part and the two outer deformation parts can undergo axial deformation when subjected to axial stress. The strain measurement fiber grating is located on the intermediate deformation section, and its two ends are respectively connected and fixed to the two first rigid connection sections one by one through fixed points.

[0007] Furthermore, the two rigid fixing parts, the two first rigid connecting parts, and the two second rigid connecting parts all adopt a solid flat plate structure.

[0008] Furthermore, the intermediate deformation portion and the two outer deformation portions both adopt a hollow ring structure. The hollow ring structure includes a rectangular hollow area and two semi-circular ring structures. The two semi-circular ring structures are symmetrically arranged at both ends of the rectangular hollow area perpendicular to the optical fiber axis. The rectangular hollow area has an axial length parallel to the optical fiber axis and a vertical length perpendicular to the optical fiber axis. The axial length is equal to the inner diameter of the semi-circular ring structure.

[0009] Furthermore, the sensor also includes a temperature-compensated fiber Bragg grating, which is disposed in the fiber groove, and one end of which is connected and fixed to the metal substrate through a corresponding fixing point.

[0010] Furthermore, the strain measurement fiber grating and the temperature compensation fiber grating are fabricated at different axial positions on the same radiation-resistant fiber, or the strain measurement fiber grating and the temperature compensation fiber grating are respectively fabricated at the same axial position on different radiation-resistant fibers.

[0011] Furthermore, the surface of the radiation-resistant optical fiber is coated with a metal coating.

[0012] Furthermore, the strain measurement fiber grating is a type II Bragg grating, which is fabricated using a femtosecond laser direct writing method.

[0013] Furthermore, the temperature-compensated fiber grating is a type II Bragg grating, which is fabricated using a femtosecond laser direct writing method.

[0014] A sensitivity adjustment method is provided for the aforementioned radiation-resistant fiber Bragg grating high-temperature strain sensor; the sensitivity adjustment method includes the following steps: During the design phase, while keeping the axial length of the metal substrate constant, the axial stiffness of the intermediate deformation portion and the two outer deformation portions is changed to adjust the sensitivity enhancement or desensitization effect of the metal substrate, thereby controlling the sensitivity coefficient of the sensor. During the assembly stage, the sensitivity coefficient of the sensor is adjusted by changing the axial distance between the two fixed points of the strain measurement fiber grating.

[0015] Furthermore, the intermediate deformation section and the two outer deformation sections all adopt the aforementioned hollowed-out ring structure; during the design phase, the axial stiffness of the intermediate deformation section and the two outer deformation sections can be adjusted by changing the vertical length of the rectangular hollowed-out area of ​​the intermediate deformation section and the inner and outer radii of the semi-circular ring structure.

[0016] The present invention has the following beneficial effects: The sensor of this invention divides the metal substrate into a rigid portion without axial deformation (the rigid fixing portion, the first rigid connecting portion, and the second rigid connecting portion) and a deformable portion capable of axial deformation (the intermediate deformable portion and the outer deformable portion). The two ends of the strain measurement fiber Bragg grating are respectively connected and fixed to the two first rigid connecting portions, so that the sensing body of the strain measurement fiber Bragg grating is located on the intermediate deformable portion. The axial strain of the object being measured is transmitted to the deformable portion only through the rigid portion, and the axial deformation generated by the deformable portion is directly transmitted to the strain measurement fiber Bragg grating. The rigid portion can avoid interference from non-target deformations to ensure the accuracy of strain transmission. In the design phase, this invention modulates the axial deformation of the metal substrate under the same axial stress by changing the axial stiffness of the intermediate deformation section and the two outer deformation sections, thereby altering the axial deformation transmitted to the strain measurement fiber grating and achieving the control of the sensor's sensitivity enhancement / desensitization effect and sensitivity coefficient. In the assembly phase, the sensitivity coefficient is fine-tuned by changing the axial distance between the two fixed points of the strain measurement fiber grating. All these adjustments are performed while maintaining the axial length of the metal substrate, without increasing the axial length of the metal substrate. This invention measures the temperature of the sensing environment by setting the temperature-compensated fiber grating, and uses the wavelength offset difference between the temperature-compensated fiber grating and the strain measurement fiber grating to decouple the temperature and strain signals, thereby improving the strain measurement accuracy. The temperature-compensated fiber grating and strain-measuring fiber grating of the present invention are fabricated within the radiation-resistant fiber. The radiation-resistant fiber has good resistance to nuclear radiation damage, can reduce radiation-induced material defects, and reduce optical power attenuation. The radiation-resistant fiber can be, but is not limited to, a fluorine-doped fiber, so that the quartz glass network structure of the fiber can be optimized by doping with fluorine, thereby reducing unstable structures such as three-membered rings and four-membered rings, and thus directly reducing the generation of radiation-induced defects. The metal coating deposited on the surface of the radiation-resistant fiber has stronger structural stability in high-temperature and high-radiation environments compared with traditional organic coatings, which can effectively protect the fiber body and further improve the radiation resistance and high-temperature resistance of the fiber. The temperature-compensated fiber grating and strain-measuring fiber grating of this invention both employ type II Bragg gratings, fabricated using a femtosecond laser direct-writing method. These gratings generate a permanent refractive index change through laser energy exceeding the damage threshold of the fiber material, resulting in high refractive index modulation. Furthermore, the thermal and radiation stability of the grating structure is far superior to that of conventional gratings, exhibiting no grating structure degradation under high-temperature and high-radiation environments. The simultaneous use of type II Bragg gratings for both the strain-measuring and temperature-compensated fiber gratings ensures completely consistent temperature response characteristics, eliminating temperature response deviations caused by differences in grating fabrication processes and types, and guaranteeing the accuracy of temperature compensation. Attached Figure Description

[0017] Figure 1 This is a schematic diagram of the structure of the radiation-resistant fiber optic grating high-temperature strain sensor provided by the present invention.

[0018] Figure 2 The parameter marking diagram is for the radiation-resistant fiber optic grating high-temperature strain sensor provided by the present invention.

[0019] Figure 3 This is a schematic diagram of the hollowed-out ring structure in the radiation-resistant fiber optic grating high-temperature strain sensor provided by the present invention.

[0020] Figure 4 This is a schematic diagram of another radiation-resistant fiber optic grating high-temperature strain sensor provided by the present invention.

[0021] Figure 5 This is a schematic diagram of another radiation-resistant fiber optic grating high-temperature strain sensor provided by the present invention.

[0022] Figure 6 A flowchart illustrating the demodulation method for the radiation-resistant fiber Bragg grating high-temperature strain sensor provided by this invention. Detailed Implementation

[0023] The present invention will now be described in detail with reference to the accompanying drawings and embodiments, examples of which are shown in the drawings, wherein the same or similar reference numerals denote the same or similar elements or elements having the same or similar functions throughout. The embodiments described below with reference to the accompanying drawings are exemplary and intended to explain the present invention, and should not be construed as limiting the present invention.

[0024] In the description of this invention, it should be understood that the terms "length", "width", "upper", "lower", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are only for the convenience of describing this invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on this invention.

[0025] Furthermore, the terms "first," "second," and "third" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Thus, a feature defined as "first," "second," or "third" may explicitly or implicitly include one or more of that feature. In the description of this invention, "multiple" means two or more, unless otherwise explicitly specified.

[0026] In this invention, unless otherwise explicitly specified and limited, the terms "installation," "connection," "linking," "fixing," and "setting," etc., should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral part; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; and they can refer to the internal communication of two components or the interaction between two components. Those skilled in the art can understand the specific meaning of the above terms in this invention according to the specific circumstances.

[0027] Example 1 like Figure 1 As shown, a radiation-resistant fiber Bragg grating high-temperature strain sensor includes a strain measurement fiber Bragg grating 11 and a metal substrate 2. The metal substrate 2 has fiber grooves along the fiber axis, and the strain measurement fiber Bragg grating 11 is disposed within the fiber grooves. The metal substrate 2 includes a central deformation portion 21 and two outer wings, which are symmetrically connected to both ends of the central deformation portion 21 along the fiber axis. Each outer wing includes a first rigid connection portion 22, an outer deformation portion 23, a second rigid connection portion 24, and a rigid fixing portion 25, which are sequentially and continuously arranged along the fiber axis. Two rigid fixing parts 25 are used to connect and fix with the object being measured; When subjected to axial stress, the two rigid fixing parts 25, the two first rigid connecting parts 22, and the two second rigid connecting parts 24 do not produce axial deformation. The intermediate deformation part 21 and the two outer deformation parts 23 can undergo axial deformation when subjected to axial stress. The strain measurement fiber grating 11 is located on the intermediate deformation part 21, and its two ends are respectively connected and fixed to the two first rigid connection parts 22 one by one through the fixing point 13.

[0028] The sensor of the present invention divides the metal substrate 2 into a rigid part without axial deformation (the rigid fixing part 25, the first rigid connecting part 22, and the second rigid connecting part 24) and a deformable part that can deform axially (the intermediate deformable part 21 and the outer deformable part 23). The two ends of the strain measurement fiber optic grating 11 are respectively connected and fixed to the two first rigid connecting parts 22, so that the sensing body of the strain measurement fiber optic grating 11 is located on the intermediate deformable part 21. The axial strain of the measured object is transmitted to the deformable part only through the rigid part, and the axial deformation generated by the deformable part is directly transmitted to the strain measurement fiber optic grating 11. The rigid part can avoid interference from non-target deformation to ensure the accuracy of strain transmission.

[0029] In this embodiment, the strain measurement fiber optic grating 11 can be connected and fixed to the two first rigid connection parts 22 of the metal substrate 2 at both ends by spot high-temperature adhesive bonding or hot melt welding, so as to form corresponding fixing points 13 respectively; the metal substrate 2 can be connected and fixed to the object under test by spot high-temperature adhesive bonding, screw screwing or hot melt welding on its two rigid fixing parts 25, so as to form corresponding connection points respectively.

[0030] When the object under test undergoes axial deformation, the axial deformation can be transmitted to the metal substrate 2 through the connection points between the two rigid fixing parts 25 and the object under test, and then transmitted to the strain measuring fiber grating 11 through the fixing points 13 between the strain measuring fiber grating 11 and the two first rigid connection parts 22, thereby causing the strain measuring fiber grating 11 to also undergo axial deformation.

[0031] When the object under test is large enough, and the total axial stiffness of the strain measurement fiber grating 11 and the metal substrate 2 is less than the stiffness of the object under test, the connection point between the metal substrate 2 and the object under test, and the fixing point 13 between the metal substrate 2 and the strain measurement fiber grating 11 are ignored. Under ideal conditions, the axial deformation between the metal substrate 2 and the object under test is the same, and the axial deformation between the intermediate deformation portion 21 of the strain measurement fiber grating 11 and the metal substrate 2 is the same.

[0032] like Figure 2 As shown, the axial stiffness and axial length of the intermediate deformation part 21 are K1 and L1, respectively; the axial stiffness and axial length of the two first rigid connecting parts 22 are K2 and L2, respectively; the axial stiffness and axial length of the two outer deformation parts 23 are K3 and L3, respectively; the axial stiffness and axial length of the two second rigid connecting parts 24 are K4 and L4, respectively; and the axial stiffness and axial length of the two rigid fixing parts 25 are K5 and L5, respectively. Under the action of axial stress F, the axial deformations generated by the intermediate deformation part 21, the first rigid connecting parts 22, the outer deformation parts 23, the second rigid connecting parts 24, and the rigid fixing parts 25 are ΔL1, ΔL2, ΔL3, ΔL4, and ΔL5, respectively, which satisfy the following formula: Then there is in, and These are the axial stiffness of each part of the metal substrate 2 and the axial deformation under axial stress F, respectively.

[0033] The axial distance between the two fixed points 13 of the strain measurement fiber optic grating 11 is The axial distance between the fixed point 13 at one end and the intermediate deformable part 21 is The axial distance between the other end fixing point 13 and the intermediate deformable part 21 is , , and The axial deformations under axial stress F are respectively , and Then there is The above formula can be simplified to in, .

[0034] The axial deformation of the strain measurement fiber grating 11 as follows: The axial deformation of the metal substrate 2 as follows: in, The axial length of the metal substrate 2 is given.

[0035] The sensitivity coefficient k of the sensor is as follows: Since the rigid fixing part 25, the first rigid connecting part 22, and the second rigid connecting part 24 do not produce axial deformation. , and It tends toward infinity. , and It tends towards zero, therefore The sensitivity coefficient k can be simplified as follows: Therefore, with the axial length L of the metal substrate 2 remaining constant, the sensitivity coefficient k of the sensor ultimately depends on the axial rigidity of the intermediate deformation portion 21. Axial stiffness of the two outer deformable parts 23 and the axial distance between the two fixed points 13 of the strain measurement fiber optic grating 11. .

[0036] Therefore, during the design phase of the sensor, while keeping the axial length L of the metal substrate 2 constant, the axial stiffness of the intermediate deformation part 21 and the two outer deformation parts 23 can be changed. , The sensitivity coefficient of the sensor is adjusted by changing the axial distance between the two fixed points 13 of the strain measurement fiber grating 11 during the assembly stage.

[0037] Specifically, when the sensitivity coefficient k < 1, the metal substrate 2 can enhance sensitivity, and when the sensitivity coefficient k > 1, the metal substrate 2 can reduce sensitivity (increase the measurement range).

[0038] Preferably, the two rigid fixing parts 25, the two first rigid connecting parts 22 and the two second rigid connecting parts 24 are all solid flat plate structures.

[0039] The solid flat plate structure has a large moment of inertia and high axial stiffness. Its axial deformation under axial stress is negligible, which can ensure that the rigid fixing part 25, the two first rigid connecting parts 22 and the two second rigid connecting parts 24 always remain rigid and no axial deformation occurs.

[0040] The intermediate deformation part 21 and the two outer deformation parts 23 all adopt a hollow ring structure, such as Figure 3 As shown, the hollow ring structure includes a rectangular hollow area 201 and two semi-circular ring structures 202. The two semi-circular ring structures 202 are symmetrically arranged at both ends of the rectangular hollow area 201 perpendicular to the optical fiber axis. The rectangular hollow area 201 has an axial length parallel to the optical fiber axis and a vertical length perpendicular to the optical fiber axis. The axial length is equal to the inner diameter of the semi-circular ring structure 202.

[0041] The hollow ring structure, through the combination design of the rectangular hollow area 201 and the semi-circular ring structure 202, forms a hollow structure with a rectangular middle section and semi-circular ends, which significantly reduces the axial stiffness of the structure and allows it to produce controllable axial deformation when subjected to axial stress. Furthermore, the axial length of the rectangular hollow area 201 is matched with the inner diameter of the semi-circular ring structure 202, making the deformation of the hollow ring structure uniform and linear. At the same time, the axial stiffness can be directly controlled by this structural parameter.

[0042] The outer radius and inner radius of the semi-circular ring structure 202 are respectively and The vertical length of the rectangular cutout area 201 is H, then When the semi-circular ring structure 202 is subjected to axial stress F, its axial deformation is as follows: When the rectangular hollow region 201 is subjected to axial stress F, its axial deformation is as follows: Where E is the elastic modulus of the metal substrate 2, and d is the thickness of the metal substrate 2. The average radius of the semi-circular ring structure 202 is... Let be the moment of inertia of the semi-circular ring structure 202. Let be the cross-sectional area of ​​the rectangular structure.

[0043] The axial stiffness of the hollowed-out annular structure is as follows: With the elastic modulus E and thickness d of the metal substrate 2 remaining constant, the axial stiffness K of the hollowed-out annular structure depends on the outer radius of the semi-circular annular structure 202. and inner radius The vertical length of the rectangular hollow area 201 is H.

[0044] Therefore, during the design phase, the axial stiffness of the intermediate deformation part 21 and the two outer deformation parts 23 can be adjusted by changing the vertical length of the rectangular hollow area 201 of the intermediate deformation part 21 and the two outer deformation parts 23, as well as the inner and outer radii of the semi-circular ring structure 202.

[0045] Preferred, such as Figure 2 As shown, the outer radius between the semi-circular ring structure 202 of the intermediate deformable part 21 and the semi-circular ring structures 202 of the two outer deformable parts 23 is... and inner radius They are all the same, at this time there is The sensitivity coefficient k can then be further expressed as: in, The vertical length of the rectangular hollow area 201 of the intermediate deformable part 21 is given by the following formula: The vertical length of the rectangular hollow area 201 of the outer deformable part 23.

[0046] In summary, the sensitivity coefficient of the sensor Mainly composed of and The proportional relationship, the outer radius of the semi-circular ring structure 202 and inner radius The vertical length of the rectangular hollow area 201 of the intermediate deformable part 21 and the outer deformable part 23 and Decision. When When, the sensitivity coefficient The reduction in size of the metal substrate 2 enhances its sensitivity; when... When, the sensitivity coefficient The increased size of the metal substrate 2 provides a desensitizing effect (increasing the measurement range). Therefore, during the design phase, the structural proportions of the hollowed-out annular structure between the intermediate deformable portion 21 and the outer deformable portion 23 are altered, especially... and The ratio between them can effectively control the sensitivity coefficient. This eliminates the need to increase the axial length of the metal substrate 2 to expand the strain measurement range. Furthermore, during the design phase, the axial distance between the two fixed points 13 of the strain measurement fiber optic grating 11 can be adjusted. and The proportional relationship can also, to some extent, regulate the strain sensitivity. .

[0047] Preferred, such as Figure 4 and 5 As shown, the sensor also includes a temperature-compensated fiber Bragg grating 12, which is disposed in the fiber groove, and one end of which is connected and fixed to the metal substrate 2 through a corresponding fixing point 13.

[0048] The temperature-compensated fiber grating 12 is fixed to the metal substrate 2 at only one end, while the other end is free, so that its wavelength shift is only affected by changes in ambient temperature and is not affected by the axial strain of the metal substrate 2. The strain-measuring fiber grating 11 is affected by both temperature and axial strain. The wavelength shift difference between the two fiber gratings can achieve signal decoupling between temperature and strain.

[0049] In one example, such as Figure 4 As shown, the strain measurement fiber grating 11 and the temperature compensation fiber grating 12 are fabricated at different axial positions on the same radiation-resistant fiber 1. The strain measurement fiber grating 11 and the temperature compensation fiber grating 12 share a common fixing point 13, enabling integrated sensor design and simplifying fiber optic deployment and packaging processes. In this case, the strain measurement fiber grating 11 and the temperature compensation fiber grating 12 have different center wavelengths, allowing for wavelength division multiplexing (WDM) technology to separate their reflected signals by combining their different center wavelengths.

[0050] In another example, such as Figure 5 As shown, the strain measurement fiber grating 11 and the temperature compensation fiber grating 12 are respectively fabricated on the same axial position of different radiation-resistant optical fibers 1 to ensure that the strain measurement fiber grating 11 and the temperature compensation fiber grating 12 are aligned with each other in a direction perpendicular to the fiber axis, so that they are in the same temperature field, thereby improving the accuracy of temperature decoupling compensation of the strain measurement fiber grating 11 by the temperature compensation fiber grating 12. In this case, the center wavelengths of the strain measurement fiber grating 11 and the temperature compensation fiber grating 12 can be the same or different.

[0051] Preferably, the surface of the radiation-resistant optical fiber 1 is coated with a metal coating.

[0052] The radiation-resistant optical fiber 1 possesses excellent resistance to nuclear radiation damage, reducing radiation-induced material defects and lowering optical power attenuation. The radiation-resistant optical fiber 1 may be, but is not limited to, a fluorine-doped optical fiber. By using fluorine doping, the quartz glass network structure of the optical fiber is optimized, thereby reducing unstable structures such as three-membered rings and four-membered rings, and thus directly reducing the generation of radiation-induced defects. The metal coating deposited on the surface of the radiation-resistant optical fiber 1 has stronger structural stability in high-temperature and high-radiation environments compared to traditional organic coatings, effectively protecting the optical fiber body and further enhancing the radiation resistance and high-temperature resistance of the optical fiber.

[0053] Preferably, both the strain measurement fiber grating 11 and the temperature compensation fiber grating 12 are type II Bragg gratings, which are fabricated using a femtosecond laser direct writing method.

[0054] The Type II Bragg grating is fabricated using a femtosecond laser direct writing method. It forms a permanent refractive index change through laser energy exceeding the damage threshold of the fiber material. It has a high refractive index modulation and its thermal and radiation stability is far superior to that of conventional gratings. There is no grating structure degradation under high temperature and high radiation environments. The strain measurement fiber grating 11 and the temperature compensation fiber grating 12 both use Type II Bragg gratings, which can also ensure that their temperature response characteristics are completely consistent, eliminating temperature response deviations caused by differences in grating fabrication processes and types, and ensuring the accuracy of temperature compensation.

[0055] Example 2 like Figure 6 As shown, a sensitivity adjustment method is used for the radiation-resistant fiber Bragg grating high-temperature strain sensor described in Example 1; the sensitivity adjustment method includes the following steps: During the design phase, while keeping the axial length of the metal substrate constant, the axial stiffness of the intermediate deformation portion and the two outer deformation portions is changed to adjust the sensitivity enhancement or desensitization effect of the metal substrate, thereby controlling the sensitivity coefficient of the sensor. During the assembly stage, the sensitivity coefficient of the sensor is adjusted by changing the axial distance between the two fixed points of the strain measurement fiber grating.

[0056] In the design phase, the sensitivity adjustment method of the present invention adjusts the axial deformation of the metal substrate under the same axial stress by changing the axial stiffness of the intermediate deformation part and the two outer deformation parts, thereby changing the axial deformation transmitted to the strain measurement fiber grating and realizing the enhancement / desensitization effect and sensitivity coefficient control of the sensor. In the assembly phase, the sensitivity coefficient is finely adjusted by changing the axial distance between the two fixed points of the strain measurement fiber grating. All the above adjustments are completed under the premise that the axial length of the metal substrate remains unchanged, without increasing the axial length of the metal substrate.

[0057] Preferably, the intermediate deformation portion and the two outer deformation portions all adopt the above-mentioned hollowed-out ring structure; during the design stage, the axial stiffness of the intermediate deformation portion and the two outer deformation portions can be adjusted by changing the vertical length of the rectangular hollowed-out area of ​​the intermediate deformation portion and the two outer deformation portions, as well as the inner and outer radii of the semi-circular ring structure.

[0058] The axial stiffness of the hollow ring structure is directly determined by the vertical length of the rectangular hollow area and the inner and outer radii of the semi-circular ring structure. Changing the above structural parameters can adjust the cross-sectional moment of inertia and overall stiffness of the hollow ring structure, thereby changing its axial deformation under the same axial stress. By adjusting the structural parameters of the middle deformation part and the two outer deformation parts respectively, the axial stiffness of each deformation part can be independently adjusted, ultimately achieving precise and controllable adjustment of the sensor sensitivity coefficient.

[0059] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the embodiments of the present invention and not to limit them. Although the embodiments of the present invention have been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can still be made to the technical solutions of the embodiments of the present invention, and these modifications or equivalent substitutions cannot cause the modified technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A radiation-resistant fiber Bragg grating high-temperature strain sensor, comprising a strain measurement fiber Bragg grating and a metal substrate, wherein the metal substrate has a fiber groove along the fiber axis, and the strain measurement fiber Bragg grating is disposed within the fiber groove; characterized in that, The metal substrate includes a central deformation portion and two outer wings. The two outer wings are symmetrically connected to both ends of the central deformation portion along the optical fiber axis. Each outer wing includes a first rigid connection portion, an outer deformation portion, a second rigid connection portion, and a rigid fixing portion arranged sequentially along the optical fiber axis. Two rigid fixing parts are used to connect and fix the object being measured; When subjected to axial stress, the two rigid fixing parts, the two first rigid connecting parts, and the two second rigid connecting parts do not produce axial deformation. The intermediate deformation part and the two outer deformation parts can undergo axial deformation when subjected to axial stress. The strain measurement fiber grating is located on the intermediate deformation section, and its two ends are respectively connected and fixed to the two first rigid connection sections one by one through fixed points.

2. The radiation-resistant fiber Bragg grating high-temperature strain sensor according to claim 1, characterized in that, The two rigid fixing parts, the two first rigid connecting parts, and the two second rigid connecting parts all adopt a solid flat plate structure.

3. The radiation-resistant fiber Bragg grating high-temperature strain sensor according to claim 1 or 2, characterized in that, The intermediate deformation section and the two outer deformation sections both adopt a hollow ring structure. The hollow ring structure includes a rectangular hollow area and two semi-circular ring structures. The two semi-circular ring structures are symmetrically arranged at both ends of the rectangular hollow area perpendicular to the optical fiber axis. The rectangular hollow area has an axial length parallel to the optical fiber axis and a vertical length perpendicular to the optical fiber axis. The axial length is equal to the inner diameter of the semi-circular ring structure.

4. The radiation-resistant fiber Bragg grating high-temperature strain sensor according to claim 1, characterized in that, The sensor also includes a temperature-compensated fiber Bragg grating, which is disposed in the fiber groove, and one end of which is connected and fixed to the metal substrate through a corresponding fixing point.

5. The radiation-resistant fiber Bragg grating high-temperature strain sensor according to claim 4, characterized in that, The strain measurement fiber grating and the temperature compensation fiber grating are fabricated at different axial positions on the same radiation-resistant fiber, or the strain measurement fiber grating and the temperature compensation fiber grating are respectively fabricated at the same axial position on different radiation-resistant fibers.

6. The radiation-resistant fiber Bragg grating high-temperature strain sensor according to claim 5, characterized in that, The surface of the radiation-resistant optical fiber is coated with a metal coating.

7. The radiation-resistant fiber Bragg grating high-temperature strain sensor according to claim 1, characterized in that, The strain measurement fiber grating is a type II Bragg grating, which is fabricated using a femtosecond laser direct writing method.

8. The radiation-resistant fiber Bragg grating high-temperature strain sensor according to claim 4, characterized in that, The temperature-compensated fiber grating is a type II Bragg grating, which is fabricated using a femtosecond laser direct writing method.

9. A sensitivity adjustment method, characterized in that, The radiation-resistant fiber Bragg grating high-temperature strain sensor according to claim 1; the sensitivity adjustment method includes the following steps: During the design phase, while keeping the axial length of the metal substrate constant, the axial stiffness of the intermediate deformation portion and the two outer deformation portions is changed to adjust the sensitivity enhancement or desensitization effect of the metal substrate, thereby controlling the sensitivity coefficient of the sensor. During the assembly stage, the sensitivity coefficient of the sensor is adjusted by changing the axial distance between the two fixed points of the strain measurement fiber grating.

10. The sensitivity adjustment method according to claim 9, characterized in that, The intermediate deformation section and the two outer deformation sections all adopt the hollow ring structure described in claim 3; during the design stage, the axial stiffness of the intermediate deformation section and the two outer deformation sections can be adjusted by changing the vertical length of the rectangular hollow area of ​​the intermediate deformation section and the inner and outer radii of the semi-circular ring structure.

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