A high-sensitivity FBG high-temperature sensor and its working and manufacturing method

Abstract

The present invention provides a high-sensitivity FBG high-temperature sensor and its working and manufacturing methods. The sensor includes two channels with different functions. One is used as a temperature compensation channel of the sensor, and the other is used as an indirect temperature measurement channel of the sensor. The two channels each contain an FBG and have the same packaging structure. The sensor has the characteristics of small size and high high-temperature sensitivity, and can connect multiple sensors in series. The invention is particularly suitable for fields involving high-temperature sensing such as aerospace, hot wells and oil fields.

Description

Technical Field

[0001] The present invention relates to the field of high temperature monitoring equipment, and in particular to a high-sensitivity FBG high temperature sensor and a working method and a manufacturing method thereof. Background Art

[0002] Fiber optic sensor is a sensor that converts the state of the object being measured into a measurable optical signal. Since the birth of fiber optic sensor, it has been widely used in many traditional sensing fields due to its advantages such as anti-electromagnetic interference, intrinsic safety, small size, light weight and easy embedding into materials.

[0003] As a new place for a country's science and technology, the aerospace field is the best embodiment of the country's comprehensive strength in science and technology. With the implementation of the country's "three deep" strategy of deep earth, deep space and deep sea, deep space has become the common development direction of various countries in the field of aerospace. However, the high temperature and strong electromagnetic interference in deep space will cause immeasurable damage to the aircraft during its service. Therefore, the reliability research of the aircraft in this harsh environment has become a focus. With the transformation of aerospace fuel, the working process of the aircraft fuel tank is in a high temperature state, and the entire structural components are in a high temperature working process. With the rapid development of science and technology, especially the implementation of the manned space program, the application field of aerospace vehicles has been continuously expanded. As a leader in the field of sensing, optical fiber sensors are very necessary to ensure the safety of people and property. Effective real-time monitoring of this harsh environment, especially high temperature environment, is very necessary. Petrochemicals are the main force of the energy industry. Petrochemicals are irreplaceable in many fields of the national economy, and the petrochemical industry is a very important industry in the national economy. In its production process, general operations are in a high temperature environment, and petroleum products are flammable and explosive. Once a fire and explosion accident occurs, it will cause great losses. With the rapid development of petrochemical industry, its safety and health monitoring is very important.

[0004] The working principle of the traditional FBG temperature sensor is that when the external temperature changes, the Bragg grating will undergo very sensitive changes, thereby reflecting back light with a wavelength different from the calibration wavelength. However, when the temperature is higher, the FBG decay phenomenon of reduced reflected light power will become more and more obvious. During the FBG manufacturing process, the carrier transitions to energy levels with different energies. The higher the energy level, the higher the energy required for decay. The higher the temperature, the fewer carriers maintain the transition state, the more severe the decay, and when the temperature is too high and exceeds the threshold, the reflected light power will become zero.

[0005] The optical fiber has good tensile properties, the maximum can reach 8000 Therefore, relying on the thermal expansion of silicone rubber to stretch the optical fiber can significantly improve the high temperature monitoring threshold of the sensor. At the same time, thanks to the good thermal effect of the expansion material, the sensor has good temperature linearity.

[0006] In terms of integration and networking, FBG has obvious advantages. Because of its very small size, each probe point only uses a very small light source component, allowing most of the light to pass through and continue to propagate. Up to 30 gratings can be used simultaneously on one optical fiber, with a transmission distance of more than 45km. This feature brings great convenience to networking. At the same time, the use of technologies such as wavelength division multiplexing has also improved the feasibility of this technology. In general, FBG has great advantages in large-scale multi-node measurements.

[0007] The existing FBG temperature sensor technology is relatively mature, but in the field of high temperature, it still has defects such as low sensitivity, low reliability, and low accuracy. Especially in high-tech fields such as aerospace, traditional sensors can no longer meet industry needs due to their non-functional deficiencies such as large functions and size, so there is an urgent need to develop a highly sensitive sensor. For high-temperature conditions in aerospace and hot well oil fields, FBG's inherent advantages enable it to have such high-sensitivity sensing capabilities under such conditions. Summary of the invention

[0008] In view of the shortcomings of existing FBG temperature sensors, the present invention provides a high-sensitivity FBG high-temperature sensor and its working and manufacturing methods. The sensor can have relatively high sensitivity in a high-temperature environment and has good linearity within the threshold, and can meet most high-temperature monitoring conditions in the fields of energy, aerospace, etc.

[0009] In order to achieve the above technical objectives, the present invention adopts the following technical solutions:

[0010] A high-sensitivity FBG high-temperature sensor, comprising:

[0011] A thermal bimetallic sandwich structure, wherein both ends of the thermal bimetallic sandwich structure are clamped by clamping structures;

[0012] The thermal bimetallic sandwich structure includes:

[0013] The thermal bimetal core layer is located at the center of the entire thermal bimetal sandwich structure and is used as the thermal flexure power source of the sensor;

[0014] The thermal bimetallic optical fiber layer comprises two layers, namely, a first thermal bimetallic optical fiber layer located on the active bending side of the thermal bimetallic core layer and a second thermal bimetallic optical fiber layer located on the passive bending side of the thermal bimetallic core layer, wherein the first thermal bimetallic optical fiber layer is provided with a first sensitivity-enhancing FBG for temperature measurement, and the second thermal bimetallic optical fiber layer is provided with a second sensitivity-enhancing FBG for temperature compensation;

[0015] The thermal bimetallic outer shell layer comprises two layers, wherein the two thermal bimetallic outer shell layers are arranged outside the two thermal bimetallic optical fiber layers;

[0016] The two layers of thermal bimetallic optical fiber layers have the same structure, both of which include a three-section structure, namely a polyimide resin ribbon located in the middle of the thermal bimetallic optical fiber layer, and two thermal bimetallic sheet units encapsulated at the upper and lower ends of the polyimide resin ribbon, wherein the polyimide resin ribbon is cured with the FBG with the coating layer peeled off by thermal curing to form a polyimide resin ribbon of the same thickness as the thermal bimetallic sheet unit.

[0017] The FBG is solidified in the polyimide resin ribbon after being solidified by the PI rubber.

[0018] The polyimide resin is doped with high temperature resistant ceramic powder and high temperature resistant metal powder for increasing the glass transition threshold temperature of the epoxy resin.

[0019] Polyimide resin: high temperature resistant ceramic powder: high temperature resistant metal powder = 1: 2.75: 7.08; the high temperature resistant metal powder is a high-fineness high temperature resistant nickel powder.

[0020] The thermal bimetallic core layer, the thermal bimetallic optical fiber layer and the thermal bimetallic outer shell layer are bonded and fixed with a PI solution, wherein the PI solution is doped with high temperature resistant ceramic powder and high temperature resistant metal powder for increasing the glass transition threshold temperature of the polyimide resin.

[0021] A working method based on the high-sensitivity FBG high-temperature sensor, when thermal deflection occurs in the thermal bimetallic core layer, the first sensitivity-enhancing FBG for temperature measurement located on the active deformation side of the thermal bimetallic core layer can identify its bending tension, thereby causing a corresponding wavelength drift; the second sensitivity-enhancing FBG for temperature compensation located on the passive deformation side of the thermal bimetallic core layer can decouple temperature and strain.

[0022] A method for manufacturing the high-sensitivity FBG high-temperature sensor comprises the following steps:

[0023] 1) Stripping of coating: Use fiber pliers to carefully peel off the coating inside the two sensitized FBG polyimide cured sections and clean them with alcohol;

[0024] 2) Annealing: Place two optical fibers with the coating layer stripped and the FBG sensitized by the stripping in a tubular furnace for annealing. First, place the fiber grating part in the middle of the tubular furnace, fix the two ends so that it is suspended in the furnace, plug the furnace openings at both ends with high-temperature cotton, heat the tubular furnace to 500°C, keep the temperature constant for 24 hours after the temperature stabilizes, take out the optical fiber and wait for it to cool to room temperature.

[0025] 3) PI-cured optical fiber: First, fix the two ends of the treated sensitized FBG on both sides of the mold, and then prepare the PI doping solution. First, heat the PI solution in a water bath. When there are no obvious bubbles, evenly add the high-temperature resistant ceramic powder and metal powder mixed according to the ratio, stir until the mixture is uniform, and cool to room temperature after no bubbles emerge. Add the curing agent to the prepared PI doping solution, stir it into the mold, and place it in a muffle furnace for curing and molding;

[0026] 8) Packaging: First, use the doped PI solution mixed with the curing agent to bond the upper and lower thermal bimetallic units located on the thermal bimetallic optical fiber layer to the thermal bimetallic core layer, and use a hot air gun to accelerate the PI curing; use the prepared PI solution to bond the polyimide resin strip cured with the optical fiber to the empty groove between the two thermal bimetallic units, and heat it repeatedly with a hot air gun until it is completely cured; then use the prepared PI solution to bond the thermal bimetallic outer shell layer to the outermost layer; put the fixed end of the sensor on the sensor and screw it on, and then use screws to fix the multi-layer thermal bimetallic layer at the other end of the sensor. Finally, put armored optical cables on both ends of the sensor to complete the packaging of the sensor.

[0027] Compared with the existing FBG temperature sensor, the present invention has the following beneficial effects:

[0028] 1. The sensor adopts a temperature compensation and temperature measurement dual FBG design. In a high temperature environment, the temperature compensation FBG can significantly eliminate the wavelength nonlinear drift caused by the temperature of the temperature measurement FBG;

[0029] 2. The sensor has a small size and occupies very little space. Multiple sensors can be integrated to realize a networked high-temperature sensing system;

[0030] 3. The sensor grating is packaged with materials with excellent thermal insulation effect. In a higher temperature field, it has higher reflected light power;

[0031] 4. The thermal bimetal used in the sensor has stable high temperature performance and can exert its thermal flexural deformation effect at a higher temperature;

[0032] 5. The sensor is suitable for various high-temperature working conditions such as hot well oil fields, aerospace, etc. It has a wide range of use and high temperature measurement sensitivity. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] Figure 1This is a schematic diagram of the structure of the high-sensitivity FBG high-temperature sensor of the present invention;

[0034] Among them, 1. sensor fixing support; (201, 202), nut; 301, thermal bimetallic core layer; 302, second thermal bimetallic optical fiber layer; 303, first thermal bimetallic optical fiber layer; 304, thermal bimetallic outer shell layer; 401, optical fiber in the second thermal bimetallic optical fiber layer; 402, optical fiber in the first thermal bimetallic optical fiber layer; 5, polyimide resin thin ribbon;

[0035] Figure 2 This is a schematic diagram of a high-sensitivity FBG high-temperature sensor without optical fiber thermal deflection according to the present invention;

[0036] Figure 3 This is a central cross-sectional view of the high-sensitivity FBG high-temperature sensor of the present invention;

[0037] Figure 4 This is a schematic diagram of the sensing system of the high-sensitivity FBG high-temperature sensor of the present invention;

[0038] Among them, 100, the high-sensitivity FBG high-temperature sensor of the present invention; 200, the armored optical cable; 300, the data processing terminal; 400, the FBG demodulator. DETAILED DESCRIPTION

[0039] According to a first embodiment of the present invention, a high-sensitivity FBG high-temperature sensor is provided.

[0040] A high-sensitivity FBG high-temperature sensor comprises a sensor fixing support 1, fixing screws 2, a thermal bimetallic core layer 301, a first thermal bimetallic optical fiber layer 303, a second thermal bimetallic optical fiber layer 303, a thermal bimetallic outer shell layer 304, a bare optical fiber 4, and a thermal insulation layer 5. After the optical fiber and the PI solution are cured, they are used together with two thermal bimetallic sheets as a thermal bimetallic optical fiber layer (302, 303), and the thermal bimetallic outer shell layer 304 is bonded to the outside. The temperature compensation FBG is located on the passive deformation side of the thermal bimetallic core layer, and the temperature measurement FBG is located on the active deformation side of the thermal bimetallic core layer.

[0041] Preferably, the temperature compensation end of the sensor leads out an armored optical cable, which can be directly connected to a demodulation device and a data analysis and processing terminal.

[0042] In the present invention, high temperature resistant ceramic powder and high temperature resistant metal powder are doped into the PI solution used for bonding, thus significantly increasing the threshold temperature of the glass transition of polyimide.

[0043] Preferably, the high temperature resistant metal powder is high fineness high temperature resistant nickel powder.

[0044] In the present invention, the innermost layer is the thermal bimetallic core layer 301, the second outer layer is the thermal bimetallic optical fiber layer, and the outermost layer is the thermal bimetallic outer shell layer 304. The first sensitive FBG for temperature measurement located on the active deformation side of the thermal bimetallic core layer 301 can directly identify the bending tension on the flexural outer side of the thermal bimetal.

[0045] Preferably, the PI strip in the sensor is tightly attached to the thermal bimetal through the PI solution.

[0046] Preferably, the sensor includes PI rubber. The PI rubber is cured to protect the FBG, and the PI rubber has very excellent high temperature resistance, which allows the FBG to maintain good working elasticity under high temperature fatigue.

[0047] In the present invention, the device is 30-100 mm long, preferably 40-80 mm, more preferably 40-60 mm, for example 50 mm. The thickness of the hot bimetallic region is 2-10 mm, more preferably 3-8 mm, for example 4 mm. The height is 5-50 mm, preferably 10-40 mm, more preferably 10-20 mm, for example 15 mm.

[0048] In the present invention, the temperature sensitivity of the sensing part used for temperature compensation is 10.5 pm / °C, and the strain sensitivity is 1.2 pm / °C. , the sensitivity of the entire sensor can reach (20-27)×1.2 pm / ℃.

[0049] A method for manufacturing a high-sensitivity FBG high-temperature sensor, the method comprising the following steps:

[0050] 1) Stripping of coating: Use fiber pliers to carefully peel off the coating inside the two sensitized FBG polyimide cured sections and clean them with alcohol;

[0051] 2) Annealing: Place two optical fibers with the coating layer stripped and sensitized FBG in a tubular furnace for annealing. First, place the fiber grating part in the middle of the tubular furnace, fix the two ends so that it is suspended in the furnace, plug the two ends of the furnace with high-temperature cotton, heat the tubular furnace to 500℃, keep the temperature constant for 24 hours after the temperature stabilizes, take out the optical fiber and wait for it to cool to room temperature.

[0052] 3) PI-cured optical fiber: First, fix the two ends of the treated sensitized FBG on both sides of the mold, and then prepare the PI doping solution. First, heat the PI solution in a water bath. When there are no obvious bubbles, evenly add the high-temperature resistant ceramic powder and metal powder mixed according to the ratio, stir until the mixture is evenly mixed, and cool to room temperature after no bubbles emerge. Add the curing agent to the prepared PI solution, stir it into the mold, and place it in a muffle furnace for curing and molding.

[0053] 4) Packaging: First, mix the curing agent with the doped PI solution, and bond the upper and lower two thermal bimetallic sheets located in the thermal bimetallic optical fiber layer (302, 303) to the thermal bimetallic core layer 301, and use a hot air gun to accelerate the PI curing. Use the prepared PI solution to bond the thermal insulation layer 5 of the PI cured with the optical fiber to the empty groove in the middle of the thermal bimetallic optical fiber layer, and heat it repeatedly with a hot air gun until it is completely cured. Then use the prepared PI solution to bond the thermal bimetallic outer shell layer 304 to the outermost layer.

[0054] Put the sensor fixed end 1 on the sensor sleeve and tighten the screws, and then fix the multi-layer thermal bimetallic layer with screws at the end different from the fixed end. Finally, put armored optical cables on both ends of the sensor to complete the packaging of the sensor.

[0055] In the present invention, step 1) is to peel off the coating layer on the surface of the optical fiber (including the grating) with an optical fiber pliers to prevent interface slippage when the sensor is working, thereby preventing a sudden change in wavelength.

[0056] In the present invention, step 2) is to place the grating part of the FBG treated in step 1) at the center of a tube furnace and keep it at a constant temperature for 24 hours, and then proceed to the subsequent steps after the temperature field is stable (the reflection wavelength tends to be stable).

[0057] Preferably, the temperature of the tube furnace is directly measured by a thermocouple located near the grating, so that the temperature obtained is closer to the actual temperature.

[0058] Preferably, the temperature compensation FBG and the temperature measurement FBG are very close, preferably 1 mm, to ensure that they have the same ambient temperature annealing process.

[0059] In the present invention, step 3) is to solidify and mold the annealed bare optical fiber and the PI rubber in a mold, so that the FBG is in a uniform stress field, and the PI rubber can well guarantee the working performance of the FBG at high temperature.

[0060] In the present invention, step 4) utilizes the thermal flexural deformation of the thermobimetal to allow the temperature measuring FBG in the active layer of the thermobimetal to recognize its bending tension, thereby causing the wavelength drift of the temperature measuring FBG.

[0061] In the present invention, the thermo bimetal used can maintain good working performance at 500°C and has a good linear ratio bending. The active layer of the thermo bimetal is composed of Mn: 75%, Ni: 15%, Cu: 10% or Ni: 20%, Mn: 6%, and the rest is iron. The thermal expansion coefficients are (20-27)×10 -6 / ℃. The passive layer composition is Ni: 36%, the rest is iron or Ni: 42%, the rest is iron, and its thermal expansion coefficient is (1.8-4.8)×10 -6 / ℃.

[0062] In the present invention, the thermal bimetal used does not adopt any special process and is currently a well-known technology.

[0063] In the present invention, the size of the thermal bimetal strip can be selected based on the actual working condition requirements and the sensitivity of the FBG.

[0064] In the present invention, the temperature measuring FBG is in a working condition where the temperature field and the strain field are coupled, and the temperature compensation FBG located on the passive deformation side of the thermal bimetallic core layer can better decouple the temperature and the strain.

[0065] In the present invention, since the sensor is very small, its integrated networking becomes very feasible, and is particularly suitable for fields requiring high-temperature sensing.

[0066] In the present invention, the outermost layer adopts thermal bimetal packaging, which can well reduce the mechanical wear of the thermal bimetal optical fiber layer.

[0067] In the present invention, the secondary outer layer uses a thermal bimetal to encapsulate the PI rubber-cured FBG. The PI rubber can effectively reduce the high-temperature damage of the FBG, and the thermal bimetal can reduce the mechanical wear of the PI rubber area.

[0068] In the present invention, the innermost layer is a thermal bimetallic strip, which is the main thermal bending power source of the sensor and can significantly enhance the sensitivity of the high-sensitivity FBG sensor.

[0069] In the present invention, because the thermal bimetal undergoes very sensitive thermal bending deformation when the temperature changes, and it can maintain good workability in a high temperature environment, when the thermal bimetal undergoes thermal bending, the temperature measuring FBG located on the active deformation side can identify its bending tension, thereby causing a corresponding wavelength drift.

[0070] In the present invention, the FBG high temperature sensor further improves the FBG temperature measurement threshold and has good feasibility.

[0071] Example 1

[0072] like Figure 1 A high-sensitivity FBG high-temperature sensor includes a sensor fixing support 1, fixing screws, a thermal bimetallic core layer 301, a thermal bimetallic optical fiber layer (302, 303), a thermal bimetallic outer shell layer 304, a bare optical fiber, and a thermal insulation layer 5.

[0073] After the optical fiber and PI solution are cured, they are used together with two thermal bimetallic sheets as a thermal bimetallic optical fiber layer, and then bonded with a thermal bimetallic outer shell layer 304. The second sensitization FBG for temperature compensation is located on the passive deformation side of the thermal bimetallic core layer, and the temperature measurement FBG is located on the active deformation side of the thermal bimetallic core layer.

[0074] The core area is mainly the hot bimetal part. The innermost is the hot bimetal core layer 301, the second outer layer is the hot bimetal fiber layer (302, 303), and the outermost is the hot bimetal shell layer 304. The temperature measuring FBG located on the active deformation side can directly identify the bending tension of the flexure outside of the hot bimetal. The size of the sensor is: length 50mm, thickness 4mm, height 15mm.

[0075] Example 2

[0076] A method for making a high-precision FBG high-temperature sensor is to fix the FBG in a tube furnace, close the tube furnace, insert high-temperature cotton at both ends, and complete the annealing process.

[0077] Example 3

[0078] Example 2 is repeated, except that the high temperature causes thermal bending deformation in the thermal bimetal region, and the first sensitive FBG used for temperature measurement located on the active deformation side of the thermal bimetal core layer can identify this bending tension.

[0079] Example 4

[0080] Example 2 is repeated, except that the high temperature causes the thermal bimetallic core layer to undergo thermal flexural deformation, and the second sensitization FBG for temperature compensation located on the passive side of the thermal bimetallic core layer can compensate for the nonlinear effect caused by temperature at high temperatures.

[0081] Example 5

[0082] Example 2 is repeated, except that the sensor further includes armored optical cables connected at both ends, the armored optical cable includes an inner cladding tube, a metal sleeve and an outer sleeve. The three-layer sleeve protects the optical fiber from corrosion, mechanical wear, shearing and other damage.

[0083] Example 6

[0084] Repeat Example 5, connect the fixed FBG high temperature sensor to the optical fiber jumper, connect it to the demodulator, and connect the demodulator end to the computer terminal. The demodulator uses the Si255 model produced by Micron Optics of the United States. It is equipped with 16 channels, each channel has a bandwidth of 160nm, and is developed based on the new generation HYPERION platform. The computer uses the ENLIGHT sensor analysis and data acquisition software on the Windows 7 operating system. Adjust the temperature setting value of the tube furnace to 500℃, start heating, and keep the temperature constant for 2h when it is heated to 500 degrees. The two FBGs are calibrated at high temperature, and the data of the temperature compensation FBG are used to compensate for the nonlinear effect of temperature on the temperature measurement FBG. The goodness of fit R2 of the two FBG data is greater than 0.9, which meets the standard of high temperature monitoring.

Claims

1. A high-sensitivity FBG high-temperature sensor, characterized in that: include: A thermal bimetallic sandwich structure, wherein two ends of the thermal bimetallic sandwich structure are clamped by clamping structures respectively; The thermal bimetallic sandwich structure includes: The thermal bimetal core layer is located at the center of the entire thermal bimetal sandwich structure and is used as the thermal flexure power source of the sensor; The thermal bimetallic optical fiber layer comprises two layers, namely, a first thermal bimetallic optical fiber layer located on the active bending side of the thermal bimetallic core layer and a second thermal bimetallic optical fiber layer located on the passive bending side of the thermal bimetallic core layer, wherein the first thermal bimetallic optical fiber layer is provided with a first sensitivity-enhancing FBG for temperature measurement, and the second thermal bimetallic optical fiber layer is provided with a second sensitivity-enhancing FBG for temperature compensation; The thermal bimetallic outer shell layer comprises two layers, wherein the two thermal bimetallic outer shell layers are arranged outside the two thermal bimetallic optical fiber layers; The two layers of thermal bimetallic optical fiber layers have the same structure, both of which include a three-section structure, namely a polyimide resin ribbon located in the middle of the thermal bimetallic optical fiber layer, and two thermal bimetallic sheet units encapsulated at the upper and lower ends of the polyimide resin ribbon, wherein the polyimide resin ribbon is cured with the FBG stripped of the coating layer by thermal curing to form a polyimide resin ribbon of the same thickness as the thermal bimetallic sheet unit; The thermal bimetallic core layer, the thermal bimetallic optical fiber layer and the thermal bimetallic outer shell layer are bonded and fixed with a PI solution, wherein the PI solution is doped with high temperature resistant ceramic powder and high temperature resistant metal powder for increasing the glass transition threshold temperature of the polyimide resin.

2. The high-sensitivity FBG high-temperature sensor according to claim 1, characterized in that: The FBG is solidified in the polyimide resin ribbon after being solidified by the PI rubber.

3. The high-sensitivity FBG high-temperature sensor according to claim 2, characterized in that: The polyimide resin thin strip is doped with high temperature resistant ceramic powder and high temperature resistant metal powder for increasing the glass transition threshold temperature of the epoxy resin.

4. The high-sensitivity FBG high-temperature sensor according to claim 3, characterized in that: Polyimide resin: high temperature resistant ceramic powder: high temperature resistant metal powder = 1:2.75:7.

08.

5. A working method based on the high-sensitivity FBG high-temperature sensor according to any one of claims 1 to 4, characterized in that: When the thermal bimetal core layer undergoes thermal bending, the first enhanced-sensitivity FBG for temperature measurement located on the active deformation side of the thermal bimetal core layer can identify its bending tension, thereby causing a corresponding wavelength drift; The second FBG for temperature compensation located on the passive deformation side of the thermal bimetallic core layer can decouple temperature from strain.

6. A method for manufacturing a high-sensitivity FBG high-temperature sensor according to any one of claims 1 to 4, characterized in that: The following steps are involved: Stripping of coating: Use fiber pliers to carefully strip off the coating inside the two sensitized FBG polyimide cured sections and clean them with alcohol; Annealing: Place two optical fibers with the coating layer stripped and sensitized FBG in a tubular furnace for annealing. First, place the fiber grating in the middle of the tubular furnace, fix both ends so that it is suspended in the furnace, plug the furnace ports at both ends with high-temperature cotton, heat the tubular furnace to 500°C, keep the temperature constant for 24 hours after the temperature stabilizes, take out the optical fiber and wait for it to cool to room temperature. PI curing optical fiber: First, fix the two ends of the treated sensitized FBG on both sides of the mold respectively, and then prepare the PI doping solution. First, heat the PI solution in a water bath. When there are no obvious bubbles, evenly add the high-temperature resistant ceramic powder and metal powder mixed according to the ratio, stir until the mixture is uniform, wait until no bubbles emerge, cool to room temperature, add curing agent to the prepared PI doping solution, stir into the mold, and place it in a muffle furnace for curing and molding; Packaging: First, mix the curing agent with the doped PI solution, bond the upper and lower thermal bimetallic sheet units located on the thermal bimetallic optical fiber layer to the thermal bimetallic core layer, and use a hot air gun to accelerate the curing of PI; The polyimide resin strip cured with the optical fiber is bonded to the empty slot between the two thermal bimetallic strip units with the prepared PI solution, and is repeatedly heated with a hot air gun until it is completely cured; the thermal bimetallic outer shell layer is then bonded to the outermost layer with the prepared PI solution; the fixed end of the sensor is put on the sensor sleeve and screwed, and the multi-layer thermal bimetallic layer is fixed to the other end of the sensor with screws, and finally, the armored optical cable is put on both ends of the sensor to complete the packaging of the sensor.

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