Preparation method of large-area decoupled fiber Bragg grating sensor based on island-bridge structure

Abstract

The present invention discloses a method for preparing a large-area decoupled fiber grating sensor based on an island bridge structure, firstly, the elastic substrate is pre-stretched on all sides, and then a plurality of carbon fiber composite sheets arranged in a matrix are bonded to the elastic substrate in a pre-stretched state, and a fiber grating and a glass fiber-coated fiber grating are respectively bonded and fixed to two rows of optical fiber positioning grooves of each row of carbon fiber composite sheets, each fiber grating has a grating point positioned in the groove of each carbon fiber composite sheet, and each groove of each carbon fiber composite sheet is filled and cured; finally, after the elastic substrate is pre-stretched and released, an elastic top sealing layer is covered on the top surface of the elastic substrate, thereby forming a large-area decoupled fiber grating sensor. The large-area decoupled fiber grating sensor prepared by the present invention can still obtain high-precision measurement results when facing high mechanical stress and dynamic deformation.

Description

Technical Field

[0001] The invention relates to the technical field of fiber grating sensors, and in particular to a method for preparing a large-area decoupled fiber grating sensor based on an island bridge structure. Background Art

[0002] At present, the types of temperature sensors mainly include thermocouples, RTDs (resistance temperature detectors) and thermistors, which are widely used in many industrial and scientific research applications. Thermocouples are favored for their wide temperature range and fast response speed, but their measurement accuracy and stability may be affected at extreme temperatures. RTDs are known for their high accuracy and stability, but they are large in size and sensitive to mechanical stress. Thermistors are usually used for smaller range measurements and are more sensitive to environmental changes. Their performance stability and reliability are poor. These limitations of traditional temperature sensors have prompted the demand for more advanced sensor technology, especially in situations where large-area monitoring and high sensitivity are required.

[0003] The main advantages of fiber Bragg grating sensors are that they can transmit signals through optical fibers, and are resistant to electromagnetic interference, high temperature resistance, and high precision. However, traditional fiber Bragg grating sensors perform poorly in large-area and high-deformation applications. Specifically, although fiber Bragg grating sensors have high temperature measurement accuracy, in large-area applications, the signal may be interfered by environmental noise, resulting in reduced measurement accuracy; conventional fiber Bragg grating sensors are usually hard and brittle, and are sensitive to mechanical deformation (such as stretching and compression), which makes them perform poorly in applications that require high stretchability. Summary of the invention

[0004] The technical problem to be solved by the present invention is to provide a method for preparing a large-area decoupled fiber grating sensor based on an island bridge structure. The prepared large-area decoupled fiber grating sensor can still obtain high-precision measurement results when facing high mechanical stress and dynamic deformation.

[0005] The technical solution of the present invention is:

[0006] The preparation method of a large-area decoupled fiber Bragg grating sensor based on an island-bridge structure specifically comprises the following steps:

[0007] (1) pre-stretching the elastic substrate on all sides, and then bonding a plurality of carbon fiber composite sheets arranged in a matrix to the top surface of the elastic substrate in the pre-stretched state, wherein two transversely extending grooves are etched on the top surface of each carbon fiber composite sheet, and the grooves on each row of carbon fiber composite sheets form two rows of optical fiber positioning grooves;

[0008] (2) While the elastic substrate is kept in a pre-stretched state, a fiber grating and a glass fiber-coated fiber grating are respectively bonded and fixed to two rows of optical fiber positioning grooves in each row of carbon fiber composite sheets, each fiber grating has a grating point positioned in the groove of each carbon fiber composite sheet, and the fiber grating is pre-stretched along each grating point of the fiber grating to ensure that the wavelength change of the fiber grating is 0.5-1.2nm, and then the fiber grating in the groove is bonded and fixed;

[0009] (3) After the two fiber gratings on each row of carbon fiber composite sheets are bonded and fixed, each groove of each carbon fiber composite sheet is filled and cured while the elastic substrate is kept in a pre-stretched state;

[0010] (4) pre-stretching and releasing the elastic substrate so that the fiber Bragg grating between two adjacent carbon fiber composite sheets on the elastic substrate retracts to form a serpentine bridge structure, that is, each fiber Bragg grating forms an island bridge structure on each row of carbon fiber composite sheets;

[0011] (5) An elastic top sealing layer is covered on the top surface of the elastic substrate. The top surface of the elastic substrate and the elastic top sealing layer are completely fixedly connected, and the elastic top sealing layer is coated on the periphery and top surface of multiple carbon fiber composite sheets. The ends of all fiber gratings in the same direction are led out from between the elastic substrate and the elastic top sealing layer, thereby forming a large-area decoupled fiber grating sensor.

[0012] The pre-stretching force of the elastic substrate reaches 100%.

[0013] The elastic base and elastic top sealing layer are both ecoflex silicone. When covering the elastic top sealing layer, the elastic base with an island bridge structure on the top surface is placed in a mold, and then liquid ecoflex silicone is added to the mold and cured to form an elastic top sealing layer on the top surface of the elastic base.

[0014] The carbon fiber composite sheet is a carbon fiber reinforced epoxy resin composite sheet.

[0015] The steps of bonding and fixing the fiber grating in the fiber positioning groove are as follows: first, the fiber grating is connected to the fiber grating demodulator, and then the grating point at the end of the fiber grating is positioned in the groove of the carbon fiber composite sheet at the end, and then the grating point in the groove is pre-stretched, and then the fiber grating in the groove is bonded and fixed, and then the subsequent section of the fiber grating with grating points is pre-stretched in sequence, and then bonded and fixed, and the above steps are repeated until all the grating points on the entire fiber grating are pre-stretched and bonded to the corresponding grooves.

[0016] Each groove of each carbon fiber composite sheet is filled with epoxy resin and completely cured.

[0017] The large-area decoupled fiber grating sensor is provided with a plurality of ventilation holes which penetrate vertically in the area where the carbon fiber composite sheet is not provided.

[0018] Advantages of the present invention:

[0019] (1) As a hard and brittle material, the optical fiber itself has limited deformation capacity during use and low robustness. The fiber grating sensor of the present invention is arranged on an elastic substrate and is a large-area fiber grating sensor with good flexibility and stretchability. It can support distributed measurement and is suitable for occasions that require coverage of a wide area and multi-point monitoring. It can adapt to large deformation environments and can also perform precise surface measurements on complex curved surfaces.

[0020] (2) The present invention adopts a carbon fiber composite sheet as the bridging part of the fiber Bragg grating island bridge structure. The carbon fiber composite sheet is a carbon fiber reinforced epoxy resin composite sheet, which has the characteristics of high rigidity, high thermal conductivity and light weight, and can effectively meet the measurement requirements of the fiber Bragg grating sensor while reducing the load on the sensor structure to a minimum.

[0021] (3) Each row of carbon fiber composite sheets of the present invention is connected to a fiber Bragg grating not coated with glass fiber and a fiber Bragg grating coated with glass fiber. The fiber Bragg grating coated with glass fiber has a good thermal insulation effect, that is, it is not affected by temperature, so that the fiber Bragg grating is only affected by strain; while the other fiber Bragg grating not coated with glass fiber is affected by both temperature and strain. By performing difference calculation on the test results of the two fiber Bragg gratings, the temperature change at the measurement position of the fiber Bragg grating sensor can be effectively decoupled, so that the temperature and strain changes can be monitored in real time. This decoupling design can sense strain and temperature separately, avoid the interference of temperature change on strain measurement, and improve the measurement accuracy.

[0022] (4) The present invention positions and connects the fiber Bragg grating (FBG) by pre-stretching the elastic substrate and then releasing the pre-stretching force, so that the fiber Bragg grating portion between the carbon fiber composite sheets forms a serpentine bending structure, and the entire fiber Bragg grating forms an island-bridge structure. The "island" portion is the main sensing area of ​​the fiber Bragg grating, and the bridging portion is used to connect adjacent "island" portions to form an integral structure. This island-bridge structure not only increases the bendability of the fiber Bragg grating, but also significantly improves its adaptability, so that the fiber Bragg grating sensor can provide more reliable measurement results in complex environments, while ensuring the stability and measurement accuracy of the fiber Bragg grating sensor under large deformation conditions.

[0023] (5) The present invention uses a pre-stretching method to stretch the elastic substrate, which can generate a preset stress distribution inside the material of the elastic substrate. By controlling the release of the elastic substrate, based on the effects of the internal pre-stored stress and elastic energy, the two-dimensional structure will spontaneously transform into a pre-designed three-dimensional shape. This pre-stretching method is simple to operate and meets the needs of the present invention for constructing an island bridge structure. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 It is a partial cross-sectional view of the large-area decoupled fiber grating sensor prepared by the present invention.

[0025] Figure 2 It is a schematic structural diagram of the carbon fiber composite sheet of the present invention.

[0026] Figure 3 It is a process state diagram of the present invention for preparing a large-area decoupled fiber grating sensor.

[0027] Figure 4 It is a structural schematic diagram of a large-area decoupled fiber grating sensor of the present invention arranged on a pipeline for leakage detection.

[0028] Figure 5 It is a schematic diagram of the structure of a large-area decoupled fiber Bragg grating sensor used in wearable devices.

[0029] Figure numerals: 1-elastic substrate, 2-carbon fiber composite sheet, 21-groove, 3-fiber Bragg grating, 4-glass fiber coated fiber Bragg grating, 5-epoxy resin, 6-elastic top sealing layer, 7-air permeability, 01-large area decoupled fiber Bragg grating sensor, 02-pipeline. DETAILED DESCRIPTION

[0030] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0031] See Figure 3 The preparation method of a large-area decoupled fiber Bragg grating sensor based on an island-bridge structure specifically comprises the following steps:

[0032] (1) An elastic substrate 1 (ecoflex silicone, with a plane area of ​​100 cm×100 cm and a height of 1 cm) is pre-stretched on all sides to a pre-stretching force of 100%. Then, three hundred and twenty-four carbon fiber composite sheets 2 (with a plane area of ​​2 cm×2 cm) arranged in a matrix (18×18) are bonded to the top surface of the elastic substrate 1 maintained in the pre-stretched state. The carbon fiber composite sheets 2 are carbon fiber reinforced epoxy resin composite sheets. The interval between adjacent carbon fiber composite sheets 2 is 3 cm. Two transversely extending grooves 21 (see FIG. 2 ) are etched on the top surface of each carbon fiber composite sheet 2. Figure 2 ), the grooves on each row of carbon fiber composite sheets 2 form two rows of optical fiber positioning grooves;

[0033] (2) When the elastic substrate 1 is kept in a pre-stretched state, a fiber grating 3 and a glass fiber-coated fiber grating 4 are respectively bonded and fixed on the two rows of fiber positioning grooves of each row of carbon fiber composite sheets 2. Each fiber grating 3 or 4 has a grating point positioned in the groove 21 of each carbon fiber composite sheet 2, and the fiber grating is pre-stretched along each grating point of the fiber grating. Specifically, the fiber grating is first connected to the fiber grating demodulator, and then the grating point at the end of the fiber grating is positioned in the groove 21 of the carbon fiber composite sheet 2 at the end, and then the grating point in the groove 21 is pre-stretched, and then the fiber grating in the groove 21 is bonded and fixed with glue, and then the subsequent section of the fiber grating with grating points is pre-stretched in sequence, and then bonded and fixed, and the above steps are repeated until all the grating points on the entire fiber grating are pre-stretched and bonded in the corresponding groove 21. The pre-stretching of the grating points ensures that the wavelength change of the fiber grating is 0.5-1.2nm;

[0034] (3) After the two optical fiber gratings 3 and 4 on each row of carbon fiber composite sheets 2 are bonded and fixed, the elastic substrate 1 is kept in a pre-stretched state, and epoxy resin 5 is filled in each groove 21 of each carbon fiber composite sheet 2 and cured for 24 hours;

[0035] (4) pre-stretching and releasing the elastic substrate 1, so that the fiber grating between two adjacent carbon fiber composite sheets 2 on the elastic substrate 1 retracts to form a serpentine bridge structure, that is, each fiber grating 3 or 4 forms an island bridge structure on each row of carbon fiber composite sheets 2;

[0036] (5) The elastic top sealing layer 6 is covered on the top surface of the elastic substrate 1. When the elastic top sealing layer 6 is covered, the elastic substrate 1 with an island bridge structure on the top surface is placed in a mold, and then liquid ecoflex silicone is added to the mold and cured, so that the top surface of the elastic substrate 1 and the elastic top sealing layer 6 are completely fixedly connected. The elastic top sealing layer 6 is coated on the periphery and top surface of the plurality of carbon fiber composite sheets 2, and the ends of all the fiber Bragg gratings 3 and 4 in the same direction are led out from between the elastic substrate 1 and the elastic top sealing layer 6, thereby forming a large-area decoupled fiber Bragg grating sensor (see Figure 1 ).

[0037] When the large-area decoupled fiber Bragg grating sensor is used, the temperature change at the measurement position of the fiber Bragg grating sensor can be decoupled, so that the changes in temperature and strain can be monitored in real time. That is, the test results of two fiber Bragg gratings (a fiber Bragg grating 3 and a glass fiber-coated fiber Bragg grating 4) are calculated by difference, so as to decouple the temperature change at the positioning position of the large-area decoupled fiber Bragg grating sensor.

[0038] The peak wavelength change of fiber Bragg grating Δλ B It is expressed as:

[0039]

[0040] Δλ B is the peak wavelength variation of the fiber Bragg grating, λ B is the central wavelength of the fiber Bragg grating, α F is the thermal expansion coefficient of the grating, ξ is the thermo-optic coefficient of the grating, P e is the elastic-optical coefficient of the fiber Bragg grating, Δε is the strain change of the grating, and ΔT is the temperature change of the grating.

[0041] Example 1

[0042] See Figure 4 In the seepage monitoring of the pipeline, the large-area decoupled fiber Bragg grating sensor 01 is bonded to the outer surface of the pipeline 02 to ensure that the fiber Bragg grating of the large-area decoupled fiber Bragg grating sensor 01 extends along the length direction of the pipeline 02. Then the fiber Bragg grating of the large-area decoupled fiber Bragg grating sensor 01 is connected to the fiber Bragg grating demodulator, and the data acquisition frequency is set to 2500 Hz to monitor the changes in temperature and strain in real time.

[0043] Different types of gases (such as air and nitrogen) and liquids (such as water and oil) are injected into the pipe 02 to monitor the temperature changes when different fluids pass through. When each fluid flows, the temperature changes in the pipe 02 are recorded to analyze the impact of the fluid on the temperature.

[0044] In a controlled laboratory environment, apply external loads to simulate actual working conditions while monitoring strain changes. Gradually increase the load and record the strain value after each increase to observe whether there is a sudden change. For the inside of pipe 02, close both ends of pipe 02, then inject gas into pipe 02 and observe the strain change of pipe 02 when the internal pressure changes.

[0045] Example 2

[0046] Combine the large-area decoupled fiber Bragg grating sensor 01 with smart wearable devices to achieve personalized and accurate physiological status monitoring. The large-area decoupled fiber Bragg grating sensor 01 not only improves user comfort, but also ensures the accuracy of data collection. In addition, the real-time data transmission and trend analysis functions greatly enhance the user's health management capabilities, enabling them to adjust their lifestyles in a timely manner and optimize health outcomes.

[0047] A large-area decoupled fiber Bragg grating sensor 01 with a plane area of ​​8 cm×8 cm was manufactured. In order to enhance air permeability, a plurality of vertically penetrating air holes 7 were provided in the area of ​​the large-area decoupled fiber Bragg grating sensor 01 where the carbon fiber composite sheet 2 was not provided (see FIG. Figure 5 ), and then use medical glue to stick the prepared large-area decoupled fiber grating sensor 01 on the human joints. The human body moves during the detection process to observe the changes in body temperature and the strain changes in the human joints during the activities.

[0048] Although embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that various changes, modifications, substitutions and variations may be made to the embodiments without departing from the principles and spirit of the present invention, and that the scope of the present invention is defined by the appended claims and their equivalents.

Claims

1. A method for preparing a large-area decoupled fiber Bragg grating sensor based on an island-bridge structure, characterized in that: The specific steps include: (1) pre-stretching the elastic substrate on all sides, and then bonding a plurality of carbon fiber composite sheets arranged in a matrix to the top surface of the elastic substrate in the pre-stretched state, wherein two transversely extending grooves are etched on the top surface of each carbon fiber composite sheet, and the grooves on each row of carbon fiber composite sheets form two rows of optical fiber positioning grooves; (2) While the elastic substrate is kept in a pre-stretched state, a fiber grating and a glass fiber-coated fiber grating are respectively bonded and fixed on two rows of fiber positioning grooves of each row of carbon fiber composite sheets, each fiber grating has a grating point positioned in the groove of each carbon fiber composite sheet, and the fiber grating is pre-stretched along each grating point of the fiber grating. Specifically, the fiber grating is first connected to the fiber grating demodulator, and then the grating point at the end of the fiber grating is positioned in the groove of the carbon fiber composite sheet at the end, and then the grating point in the groove is pre-stretched, and then the fiber grating in the groove is bonded and fixed, and then the subsequent section of the fiber grating with grating points is pre-stretched in sequence, and then bonded and fixed again, and the above steps are repeated until all the grating points on the entire fiber grating are pre-stretched and bonded in the corresponding grooves, and the pre-stretching of the grating points ensures that the wavelength change of the fiber grating is 0.5-1.2nm; (3) After the two fiber gratings on each row of carbon fiber composite sheets are bonded and fixed, each groove of each carbon fiber composite sheet is filled and cured while the elastic substrate is kept in a pre-stretched state; (4) pre-stretching and releasing the elastic substrate so that the fiber Bragg grating between two adjacent carbon fiber composite sheets on the elastic substrate retracts to form a serpentine bridge structure, that is, each fiber Bragg grating forms an island bridge structure on each row of carbon fiber composite sheets; (5) An elastic top sealing layer is covered on the top surface of the elastic substrate. The top surface of the elastic substrate and the elastic top sealing layer are completely fixedly connected, and the elastic top sealing layer is coated on the periphery and top surface of multiple carbon fiber composite sheets. The ends of all fiber gratings in the same direction are led out from between the elastic substrate and the elastic top sealing layer, thereby forming a large-area decoupled fiber grating sensor.

2. The method for preparing a large-area decoupled fiber Bragg grating sensor based on an island-bridge structure according to claim 1, characterized in that: The pre-stretching force of the elastic substrate reaches 100%.

3. The method for preparing a large-area decoupled fiber Bragg grating sensor based on an island-bridge structure according to claim 1, characterized in that: The elastic base and elastic top sealing layer are both ecoflex silicone. When covering the elastic top sealing layer, the elastic base with an island bridge structure on the top surface is placed in a mold, and then liquid ecoflex silicone is added to the mold and cured to form an elastic top sealing layer on the top surface of the elastic base.

4. The method for preparing a large-area decoupled fiber grating sensor based on an island-bridge structure according to claim 1, characterized in that: The carbon fiber composite sheet is a carbon fiber reinforced epoxy resin composite sheet.

5. The method for preparing a large-area decoupled fiber Bragg grating sensor based on an island-bridge structure according to claim 1, characterized in that: Each groove of each carbon fiber composite sheet is filled with epoxy resin and completely cured.

6. The method for preparing a large-area decoupled fiber Bragg grating sensor based on an island-bridge structure according to claim 1, characterized in that: The large-area decoupled fiber grating sensor is provided with a plurality of ventilation holes which penetrate vertically in the area where the carbon fiber composite sheet is not provided.

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