A pre-embedded fiber optic strain sensor

Abstract

This invention provides a pre-embedded fiber Bragg grating strain sensor, relating to the field of strain measurement technology. It includes a heat-insulating sleeve, a substrate, and an optical fiber. The heat-insulating sleeve has a through-channel, and its outer end face has a roughened portion. The elastic modulus of the heat-insulating sleeve is adapted to concrete. Both the substrate and the optical fiber pass through the through-channel. The substrate has an elastic ring and fixing portions located at both ends of the elastic ring. Both sets of fixing portions radially support the through-channel. A sealed heat-insulating structure is provided between the fixing portions and the through-channel. The optical fiber has two fiber Bragg gratings, one of which is fixed to one of the fixing portions, and the other has its two ends fixed to the opposite ring walls of the elastic ring. The through-channel is filled with a strain transfer medium. This invention optimizes the packaging structure of the pre-embedded fiber Bragg grating strain sensor, effectively protecting the fiber Bragg grating while improving strain transfer efficiency and reducing temperature interference.

Description

Technical Field

[0001] This utility model relates to the field of strain measurement technology, and in particular to a pre-embedded fiber optic strain sensor. Background Technology

[0002] Fiber Bragg gratings (FBGs) employ a wavelength coding mechanism to convert changes in monitored physical information (such as temperature, pressure, vibration, displacement, etc.) into changes in the wavelength of optical signals. This technology has strong anti-interference capabilities and is easy to network and multiplex, making it suitable for most complex application environments.

[0003] However, the grating itself is made of silicon dioxide, which is thin and fragile with poor shear resistance. Embedded fiber Bragg grating strain sensors often operate in complex concrete environments, and their encapsulation quality parameters (such as materials and structure) directly affect the degradation of temperature sensing performance. Therefore, effective protection and encapsulation of embedded fiber Bragg grating strain sensors has become a crucial aspect of their application in various fields. For this purpose, thick, round steel tubes are typically used to encapsulate and protect the fiber Bragg grating.

[0004] However, this thick-walled rigid metal tube encapsulation causes two main problems. First, low strain transfer efficiency: the excessive thickness and high rigidity of the steel tube make it difficult for concrete strain to be efficiently transferred to the internal fiber optic grating, resulting in a significant rigidity mismatch in the mechanical path. At the same time, slippage is prone to occur between the steel tube and the concrete interface, and the rigidity of the steel tube itself will share some of the stress, further weakening the measured strain transferred to the grating. Second, significant temperature interference: the thermal expansion coefficients of the steel tube, concrete, and optical fiber materials differ greatly. Temperature changes will generate significant additional strain inside the sensor, directly affecting the sensor's sensitivity and accuracy in detecting strain. Utility Model Content

[0005] Based on this, the purpose of this utility model is to provide a pre-embedded fiber Bragg grating strain sensor, which aims to optimize the packaging structure of the pre-embedded fiber Bragg grating strain sensor, thereby effectively protecting the fiber Bragg grating while improving strain transfer efficiency and reducing temperature interference.

[0006] To achieve the above objectives, this utility model proposes a pre-embedded fiber optic strain sensor, comprising a heat-insulating sleeve, a substrate, and an optical fiber. The heat-insulating sleeve has an axially extending channel, and its outer end face has a roughened portion. The elastic modulus of the heat-insulating sleeve is adapted to the concrete. The substrate passes through the extending channel and has an elastic ring and fixing portions located at both ends of the elastic ring. The elastic ring is completely located within the extending channel and is spaced from the inner wall of the extending channel. Two sets of fixing portions extend partially outside the extending channel. Each of the fixed parts radially supports the through channel. The fixed part and the through channel are sealed and heat-insulated. The optical fiber passes through the through channel and has two fiber Bragg gratings. One fiber Bragg grating is fixed to one of the fixed parts and located inside the through channel. The two ends of the other fiber Bragg grating are fixed to the opposite ring walls of the elastic ring. The through channel is filled with a strain transfer medium whose elastic modulus is less than that of the fiber Bragg grating fixed to the fixed part.

[0007] In addition, the pre-embedded fiber optic strain sensor according to the present invention may also have the following additional technical features:

[0008] Furthermore, the through channel is stepped, and the size of the middle part of the through channel is larger than the size of the openings at both ends, and the size of the openings at both ends of the through channel is larger than the size of the optical fiber.

[0009] Furthermore, the heat insulation sleeve has a recessed cavity at the position corresponding to the fiber Bragg grating fixed on the fixing part.

[0010] Furthermore, the edges of the concave cavity are inclined.

[0011] Furthermore, the strain transfer medium includes epoxy resin, polyimide, polytetrafluoroethylene, and silicone rubber.

[0012] Furthermore, the through channel is circular, and the fixing part includes an adjacent solid disk and a cylindrical block. The solid disk is completely located inside the through channel, and the cylindrical block extends outside the through channel. One of the fiber Bragg gratings is fixed on one of the cylindrical blocks.

[0013] Furthermore, the solid disk is arranged perpendicularly to the elastic ring.

[0014] Furthermore, a clamping block is fitted onto the cylindrical block, and an installation structure is provided on the clamping block. The opening edge of the heat insulation sleeve is provided with a flange, and one end of the clamping block near the heat insulation sleeve is provided with a groove that matches the flange. A first sealing ring is provided in the groove.

[0015] Furthermore, a second sealing ring is provided between the end of the clamping block away from the heat insulation sleeve and the cylindrical block.

[0016] The beneficial effects of this utility model include at least the following: by adopting an insulating sleeve with an elastic modulus adapted to concrete and an internal elastic ring structure, the rigidity mismatch problem caused by traditional rigid steel pipe encapsulation is effectively alleviated, the transmission efficiency of concrete strain to fiber Bragg grating is improved, the insulating sleeve and the fixed part of the sealed connection form a double thermal insulation barrier, which greatly reduces the additional strain caused by the difference in thermal expansion coefficients between steel pipe and concrete, improves temperature stability, thereby isolating the direct interference of external temperature fluctuations on the grating, improving the accuracy and reliability of strain detection, the rough part design increases the interface friction between the sleeve and concrete, suppresses slippage, and the stepped through channel and sealing ring structure ensure the airtightness of the encapsulation and prevent the intrusion of moisture or corrosive media. Attached Figure Description

[0017] Figure 1 This is a schematic diagram of the structure of a pre-embedded fiber optic strain sensor in one embodiment of the present invention;

[0018] Figure 2 This is an assembly diagram of the first sealing ring and the second sealing ring in one embodiment of the present invention;

[0019] Explanation of key component symbols:

[0020] Insulation sleeve 100, through channel 110, cavity 120, flange 130, substrate 200, elastic ring 210, fixing part 220, solid disk 221, cylindrical block 222, optical fiber 300, fiber Bragg grating 310, clamping block 400, groove 410, first sealing ring 500, second sealing ring 600;

[0021] The following detailed description, in conjunction with the accompanying drawings, will further illustrate this utility model. Detailed Implementation

[0022] To facilitate understanding of this utility model, a more complete description will be given below with reference to the accompanying drawings. Several embodiments of this utility model are shown in the drawings. However, this utility model can be implemented in many different forms and is not limited to the embodiments described herein. Rather, these embodiments are provided so that the disclosure of this utility model will be more thorough and complete.

[0023] It should be noted that when a component is said to be "fixed to" another component, it can be directly on the other component or there may be an intervening component. When a component is said to be "connected to" another component, it can be directly connected to the other component or there may be an intervening component. The terms "vertical," "horizontal," "left," "right," and similar expressions used in this document are for illustrative purposes only.

[0024] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. The term "and / or" as used herein includes any and all combinations of one or more of the associated listed items.

[0025] Please refer to Figures 1 to 2 The present invention provides a pre-embedded fiber optic grating strain sensor, comprising a heat insulation sleeve 100, a substrate 200, and an optical fiber 300.

[0026] Specifically, the insulation sleeve 100 has a through channel 110 along its axial direction, and the outer end face of the insulation sleeve 100 has a roughened portion (not shown in the figures). The roughened portion is designed to enhance the bond strength with the surrounding concrete and ensure effective strain transfer. Optionally, the roughened portion can be a surface roughening treatment, a ribbed or threaded structure, and the material can be a cement-based composite material. Furthermore, to ensure effective strain transfer, the elastic modulus of the insulation sleeve 100 is adapted to the concrete. Optionally, the insulation sleeve 100 can be manufactured using ceramic fiber reinforced polymer composite materials, microporous silicate or aerogel composite materials, or cement-based composite materials, achieving both insulation and effective strain transfer.

[0027] The substrate 200 has a through-channel 110 and is provided with an elastic ring 210 and fixing portions 220 located at both ends of the elastic ring 210. The elastic ring 210 is completely located within the through-channel 110, and a gap is provided between the elastic ring 210 and the inner wall of the through-channel 110, so that the elastic ring 210 does not directly contact the heat insulation sleeve 100, preventing the elastic ring 210 from being subjected to radial force. The two sets of fixing portions 220 extend partially outside the through-channel 110, and both sets of fixing portions 220 partially support the through-channel 110 radially, that is, the fixing portions 220 directly contact the inner wall of the through-channel 110 to prevent the heat insulation sleeve 100 from radially deforming, thereby improving the overall strength of the heat insulation sleeve 100. In order to prevent external concrete and moisture from entering the through-channel 110, the fixing portions 220 and the through-channel 110 are sealed. At the same time, in order to prevent the through-channel 110 from being affected by the external temperature, the fixing portions 220 and the through-channel 110 are heat-insulated.

[0028] An optical fiber 300 passes through a through-channel 110, and the optical fiber 300 has two fiber Bragg gratings 310 spaced apart by a certain wavelength along its axial direction. The left fiber Bragg grating 310 is fixed to the left fixing part 220 and located within the through-channel 110, while the two ends of the right fiber Bragg grating 310 are fixed to the opposite ring walls of an elastic ring 210. The middle of the fiber Bragg grating traverses the hollow area in the middle of the elastic ring 210. Preferably, to effectively transfer strain, the elastic modulus of the fixing part 220 is much greater than the elastic modulus of the elastic ring 210. It should be noted that the fiber Bragg gratings 310 can be fixed by bonding or welding.

[0029] In this embodiment, to effectively transfer strain, the through-channel 110 is filled with a strain transfer medium whose elastic modulus is smaller than that of the fiber Bragg grating 310 fixed on the fixing part 220. Simultaneously, since the fiber Bragg grating 310 on the right is suspended above the middle elastic ring 210, strain transfer loss that might occur with direct fixing is avoided. Therefore, the strain it measures is the actual strain between the two fixing points. The deformation of the concrete structure is transferred to the elastic ring 210 through the fixing part 220, causing deformation of the middle elastic ring 210, which in turn causes a change in the wavelength of the fiber Bragg grating 310 on the right. Conversely, since the elastic modulus of the fixing part 220 on the left is much larger than that of the elastic ring 210, the fixing part 220 is not affected by strain. This means that the fiber Bragg grating 310 on the left is only affected by temperature changes and can be used for temperature compensation.

[0030] In some alternative embodiments, such as Figure 1As shown, the through channel 110 is stepped, and the size of the middle part of the through channel 110 is larger than the size of the openings at both ends, so as to prevent the substrate 200 from being moved out of the through channel 110. The size of the openings at both ends of the through channel 110 is larger than the size of the optical fiber 300, so as to facilitate the optical fiber 300 to pass through the through channel 110.

[0031] In some alternative embodiments, such as Figure 1 As shown, the heat insulation sleeve 100 and the fiber Bragg grating 310 fixed on the fixing part 220 are provided with a cavity 120 to further prevent the heat insulation sleeve 100 from slipping on the concrete.

[0032] In some alternative embodiments, such as Figure 1 As shown, the edge of the cavity 120 is inclined. This design allows the stress flow line to change smoothly, reducing the stress concentration at the cavity 120 of the insulation sleeve 100, which could damage the overall structure of the insulation sleeve 100.

[0033] In some optional embodiments, the strain transfer medium includes epoxy resin, polyimide, polytetrafluoroethylene, and silicone rubber. Since the elastic modulus of the strain transfer medium is lower than that of the fiber Bragg grating 310, external pressure can compress the polymer body within the penetrating channel 110 through the fixing part 220. The polymer body can then smoothly transfer strain to the elastic ring 210, at which point the elastic ring 210 generates axial stress, thereby causing axial strain in the fiber Bragg grating 310.

[0034] In some alternative embodiments, such as Figure 1 As shown, the through channel 110 is circular, and the fixing part 220 includes a solid disk 221 and a cylindrical block 222 adjacent to each other. The solid disk 221 is completely located inside the through channel 110, and the edge of the solid disk 221 contacts the inner wall of the through channel 110. The cylindrical block 222 extends to the outside of the through channel 110, and the fiber Bragg grating 310 on the left is fixed on the cylindrical block 222 on the left.

[0035] In some alternative embodiments, such as Figure 1 As shown, the solid disc 221 and the elastic ring 210 are arranged perpendicularly. In this embodiment, the elastic ring 210 and the vertically arranged solid disc 221 work together to allow micro-deformation to transmit strain, while maintaining the overall structural strength through radial support, enabling the sensor to adapt to the long-term embedding requirements of complex concrete environments.

[0036] In some alternative embodiments, such as Figure 2As shown, a clamping block 400 is fitted onto the cylindrical block 222. The clamping block 400 has an installation structure, such as a bolt mounting structure, to facilitate the pre-embedding and positioning of the sensor. The opening edge of the heat insulation sleeve 100 has a flange 130. One end of the clamping block 400 near the heat insulation sleeve 100 has a groove 410 that matches the flange 130. A first sealing ring 500 is provided in the groove 410. In use, the flange 130 is inserted into the groove 410, thereby aligning the heat insulation sleeve 100 and the clamping block 400. Then, the clamping block 400 and the heat insulation sleeve 100 are fixed together by fasteners. At the same time, the first sealing ring 500 ensures the waterproof and dustproof performance of the sensor end.

[0037] In some alternative embodiments, such as Figure 2 As shown, a second sealing ring 600 is provided between the end of the clamping block 400 away from the heat insulation sleeve 100 and the cylindrical block 222. The second sealing ring 600 further ensures the waterproof and dustproof performance of the sensor end.

[0038] In the description of this specification, the references to terms such as "one embodiment," "some embodiments," "example," "specific example," or "some examples," etc., indicate that a specific feature, structure, material, or characteristic described in connection with that embodiment or example is included in at least one embodiment or example of the present invention. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples.

[0039] The above-described embodiments are merely illustrative of several implementations of this utility model, and while the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of protection of this utility model. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of this utility model, and these all fall within the scope of protection of this utility model. Therefore, the scope of protection of this utility model should be determined by the appended claims.

Claims

1. A pre-embedded fiber optic strain sensor, characterized in that, The embedded fiber optic strain sensor includes: The heat insulation sleeve has an axial through-channel and a rough portion on its outer end face. The elastic modulus of the heat insulation sleeve is adapted to the concrete. A substrate is provided with the through channel, and the substrate is provided with an elastic ring and fixing parts disposed at both ends of the elastic ring. The elastic ring is completely located inside the through channel and is separated from the inner wall of the through channel. The two sets of fixing parts extend partially outside the through channel, and both sets of fixing parts partially radially support the through channel. The fixing parts and the through channel are sealed and heat-insulated. An optical fiber passes through the through-channel and has two fiber Bragg gratings. One of the fiber Bragg gratings is fixed on one of the fixing parts and located inside the through-channel, while the two ends of the other fiber Bragg grating are fixed on the opposite ring walls of the elastic ring. The through-channel is filled with a strain transfer medium whose elastic modulus is less than that of the fiber Bragg grating fixed to the fixing part.

2. The embedded fiber optic strain sensor according to claim 1, characterized in that, The through-channel is stepped, and the size of the middle part of the through-channel is larger than the size of the openings at both ends, and the size of the openings at both ends of the through-channel is larger than the size of the optical fiber.

3. The embedded fiber optic strain sensor according to claim 1, characterized in that, The heat insulation sleeve has a recessed cavity at the position corresponding to the fiber Bragg grating fixed on the fixing part.

4. The embedded fiber optic strain sensor according to claim 3, characterized in that, The edges of the concave cavity are inclined.

5. The embedded fiber optic strain sensor according to claim 1, characterized in that, The strain transfer medium includes epoxy resin, polyimide, polytetrafluoroethylene, and silicone rubber.

6. The embedded fiber optic strain sensor according to claim 1, characterized in that, The through channel is circular, and the fixing part includes an adjacent solid disk and a cylindrical block. The solid disk is completely located inside the through channel, and the cylindrical block extends outside the through channel. One of the fiber Bragg gratings is fixed on one of the cylindrical blocks.

7. The embedded fiber optic strain sensor according to claim 6, characterized in that, The solid disk is positioned perpendicular to the elastic ring.

8. The embedded fiber optic strain sensor according to claim 6, characterized in that, A clamping block is fitted onto the cylindrical block, and an installation structure is provided on the clamping block. A flange is provided at the opening edge of the heat insulation sleeve, and a groove matching the flange is provided at one end of the clamping block near the heat insulation sleeve. A first sealing ring is provided in the groove.

9. The embedded fiber optic strain sensor according to claim 8, characterized in that, A second sealing ring is provided between the end of the clamping block away from the heat insulation sleeve and the cylindrical block.

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