Fiber bragg grating strain gauge
By integrally casting the optical fiber and substrate to form a fiber optic strain gauge with an integrated structure, the measurement accuracy and reliability issues in existing technologies are solved, the mechanical strength is enhanced, it is suitable for high-temperature environments, the packaging difficulty and cost are reduced, the application range is expanded, and the yield and service life are improved.
Patent Information
- Application Number
- CN202520718795.3
- Authority / Receiving Office
- CN · China
- Patent Type
- Utility models(China)
- Current Assignee / Owner
- Filing Date
- 2025-04-16
- Publication Date
- 2026-02-24
- Estimated Expiration
- 2035-04-16
AI Technical Summary
Existing fiber Bragg grating strain gauges suffer from problems such as difficulty in ensuring measurement accuracy and reliability, insufficient mechanical strength, high packaging difficulty, inability to be used in high-temperature environments, low yield, fixed force direction, limited application range, difficult processing, high cost, and poor integration.
The optical fiber is embedded in the substrate by integral casting. The substrate is a fully sealed structure. The exposed end of the optical fiber is sealed by encapsulation tube. The encapsulation methods include fusion bonding, serrated protrusion embedding and flexible buffer layer fixation to form an integral structure.
It improves measurement accuracy and reliability, enhances mechanical strength, is suitable for high-temperature environments, reduces packaging difficulty and cost, expands the scope of application, simplifies the installation process, and improves yield and service life.
Smart Images
Figure CN223940229U_ABST
Abstract
Description
Technical Field
[0001] This utility model belongs to the field of sensor element technology, specifically relating to a fiber optic strain gauge. Background Technology
[0002] Almost all types of public infrastructure, including bridges, pipelines, tunnels, foundations, roads, and dams, are susceptible to performance degradation or malfunctions. These structural problems can be caused by deterioration, improper construction methods, seismic activity, or nearby construction work, thus requiring long-term monitoring of these structures using monitoring devices. However, in practical applications, these monitoring devices need to withstand drastic temperature changes, ranging from approximately -270°C to 300°C, and may also be exposed to strong electromagnetic fields. As a commonly used monitoring device, the resistance strain gauge's measured values are affected when the ambient magnetic field reaches a certain intensity, and the degree of this effect is positively correlated with the intensity of the changing magnetic field. Therefore, resistance strain gauges cannot meet the requirements for long-term monitoring.
[0003] Fiber Bragg grating strain gauges utilize fiber Bragg grating sensing technology to sense and measure displacement changes. Due to their advantages such as fast response, multiplexing, corrosion resistance, and electromagnetic interference resistance, they have been widely used in the field of structural health monitoring in civil engineering. In existing fiber Bragg grating displacement sensors, fiber Bragg gratings are often packaged using surface-mount or end-fixed methods. Surface-mounting involves directly attaching the fiber Bragg grating to the outer wall of the substrate of elastic sensitive elements such as cantilever beams, so that the deformation of the substrate is converted into strain of the fiber Bragg grating, thereby causing a shift in the center wavelength of the grating. However, it has the following shortcomings: (1) Measurement accuracy and reliability are difficult to guarantee: The use of adhesive will affect the accuracy and reliability of the strain gauge because the adhesive will introduce nonlinear strain or temperature dependence. (2) It is greatly affected by temperature changes: The surface-mounted strain gauge packaging method is easily affected by temperature changes because the thermal expansion coefficients of the strain gauge and the adhesive may be different, leading to an increase in error. (3) Insufficient mechanical strength: The surface-mounted strain gauge packaging method has low mechanical strength and is easily affected by mechanical impact and vibration, which may cause the strain gauge to fall off or be damaged. (4) High packaging difficulty: The packaging process requires highly precise process control to ensure that the position and orientation of the strain gauge are correct, otherwise it will affect the accuracy and reliability. (5) Cannot be used in high temperature environments: The surface-mount strain gauge packaging method cannot be used in high temperature environments because the adhesive will decompose or fail, causing the strain gauge to fall off or be damaged. (6) Low yield: Surface-mount is prone to problems such as glue leakage and poor sealing during bonding, resulting in a low yield. Moreover, the yield is also subject to the bonding technique.
[0004] The two-end fixed type involves attaching and fixing the two ends of the optical fiber outside the grating area, converting the axial strain of the fiber optic grating into the drift of the grating center wavelength. This method has the following shortcomings: (1) Fixed force direction: The two-end fixed strain gauge can only measure the strain in a specific direction and cannot measure the strain in other directions. Therefore, in application, it is necessary to select the appropriate strain gauge direction and make corresponding corrections. (2) Insufficient mechanical strength: The mechanical strength of the two-end fixed strain gauge packaging method is low, and it is easily affected by mechanical impact and vibration, which can lead to the strain gauge falling off or being damaged. (3) High packaging difficulty: The packaging process requires highly precise process control, and it is necessary to ensure that the position and direction of the strain gauge are correct, otherwise it will affect the accuracy and reliability. (4) Cannot be used in high temperature environment: The two-end fixed strain gauge packaging method cannot be used in high temperature environment because the adhesive will decompose or fail, leading to the strain gauge falling off or being damaged. (5) Limited scope of application: The two-end fixed strain gauge is suitable for measuring a small strain range and strain, but not for measuring a large strain.
[0005] Furthermore, most existing fiber Bragg grating strain sensors currently use metal encapsulation. However, due to the high strength and elastic modulus of metal, there are drawbacks such as affecting the physical properties of the measured object and failing to accurately reflect the true strain value of the measured object. This phenomenon is particularly prominent when the measured object is small in size or the material strength is low. Moreover, metal-encapsulated sensors are difficult to manufacture and expensive. Alternatively, thin plastic sheets are used to encapsulate fiber Bragg grating strain sensors, but the disadvantages of thin plastic sheet encapsulation are: poor integrity, the thin plastic sheet is easy to detach, and the bonding process can easily cause some damage to the optical fiber.
[0006] Therefore, in order to address the above-mentioned technical problems, it is necessary to provide a fiber optic strain gauge.
[0007] The information disclosed in this background section is intended only to enhance the understanding of the overall background of this utility model and should not be construed as an admission or in any way implying that the information constitutes prior art known to those skilled in the art. Utility Model Content
[0008] The purpose of this invention is to provide a fiber optic strain gauge that can solve the problems of existing technologies, such as difficulty in ensuring measurement accuracy and reliability, insufficient mechanical strength, high packaging difficulty, inability to be used in high-temperature environments, low yield, fixed force direction, limited application range, difficult processing, high cost, and poor integration.
[0009] To achieve the above objectives, the technical solution provided by a specific embodiment of this utility model is as follows:
[0010] A fiber optic strain gauge includes an optical fiber, a substrate, and a pair of encapsulation tubes. The optical fiber is integrally embedded in the substrate by casting. The substrate has a fully sealed structure. Both ends of the optical fiber are exposed. The exposed ends of the optical fiber are sealed by a pair of encapsulation tubes. A fixing structure is provided between the optical fiber and the encapsulation tubes.
[0011] One end of each pair of encapsulation tubes is inserted into the interior of the substrate, and a fusion bonding portion is provided between each pair of encapsulation tubes and the substrate. The length of the fusion bonding portion accounts for 1 / 3 to 1 / 5 of the total length of the encapsulation tube.
[0012] In one or more embodiments of this utility model, the fixing structure is directly formed by heating and encapsulating the tube and fusing it with the optical fiber and then bonding it to the surface of the optical fiber.
[0013] In one or more embodiments of this utility model, the fixing structure includes a protrusion structure disposed inside the encapsulation tube, and the encapsulation tube clamps the end of the optical fiber through the protrusion structure.
[0014] In one or more embodiments of this utility model, the protrusion structure includes multiple sets of sawtooth protrusions, which are circumferentially distributed on the inner wall of the encapsulation tube, and are embedded in the surface of the optical fiber during high-temperature casting of the substrate.
[0015] In one or more embodiments of this utility model, the encapsulation tube is formed by molding multiple sets of serrated protrusions through an inner wall mold.
[0016] In one or more embodiments of this utility model, the fixing structure includes a flexible buffer layer disposed between the optical fiber and the encapsulation tube, wherein the flexible buffer layer is fixed to the end of the optical fiber by low-temperature curing.
[0017] In one or more embodiments of this utility model, the flexible buffer layer includes a flexible epoxy resin filling layer, which is formed by injecting flexible epoxy resin slurry and curing it at low temperature.
[0018] In one or more embodiments of this utility model, the thickness of the substrate is 0.2-2.0 mm.
[0019] In one or more embodiments of this utility model, the inner diameter of the encapsulation tube is 0.12-1.8 mm.
[0020] In one or more embodiments of this utility model, the encapsulation tube is a fusible polytetrafluoroethylene tube.
[0021] Compared with the prior art, the present invention has the following beneficial effects:
[0022] 1. High measurement accuracy
[0023] In this invention, the optical fiber is integrally cast and embedded in a substrate, wherein the substrate is a fully sealed structure, and the exposed end of the optical fiber is sealed by an encapsulation tube. By integrally casting the optical fiber and substrate, this invention forms a single unit. In use, fixing the substrate to the object being measured is equivalent to directly fixing the optical fiber to the object, ensuring complete contact between the strain gauge and the object, thus making the strain gauge measurements more accurate.
[0024] 2. The measurement results are reliable.
[0025] This invention, by integrally casting the optical fiber and substrate, ensures that the optical fiber and substrate form a whole, making them less prone to detachment or displacement, and resulting in more stable and reliable measurement results.
[0026] 3. Excellent overall performance and high strength
[0027] The optical fiber of this invention is integrally cast and embedded in the substrate, resulting in good overall performance and high strength.
[0028] 4. Long service life
[0029] This invention involves casting the optical fiber and substrate together as a single unit. This integral molding process makes the fiber less susceptible to damage or destruction from external forces, resulting in greater durability and a longer service life.
[0030] 5. Suitable for high-temperature environments
[0031] This invention involves integrally casting the optical fiber and substrate into a strain gauge. The integrally cast strain gauge provides excellent high-temperature protection and is suitable for strain measurement in high-temperature environments.
[0032] 6. Aesthetically pleasing
[0033] This invention involves integrally casting the optical fiber and substrate, resulting in a strain gauge that can be completely integrated with the object being measured, thus achieving a more aesthetically pleasing appearance.
[0034] 7. Easy to package and reliable structure.
[0035] The optical fiber of this invention is integrally cast and embedded in a substrate, making encapsulation easy. The exposed end of the optical fiber is sealed using an encapsulation tube. There are three encapsulation methods: First, the encapsulation tube is heated to achieve fusion bonding with the optical fiber and adhere to the fiber surface, while the substrate is simultaneously heated, creating a physical interlock between the encapsulation tube and the substrate. After cooling, an integrated sealed structure is formed. Second, the encapsulation tube is molded with serrated protrusions on its inner wall. After the optical fiber is inserted, the substrate expands during high-temperature casting, pushing the protrusions of the encapsulation tube into the fiber surface. After cooling, the substrate shrinks, and the protrusion structure permanently secures the optical fiber. Third, a flexible buffer layer is formed by injecting flexible epoxy resin slurry into the gap between the encapsulation tube and the optical fiber. Low-temperature curing achieves metal-free fixation, and the outer encapsulation tube is bonded to the substrate, providing high-temperature protection. All three encapsulation methods ensure reliable fixation of the optical fiber within the encapsulation tube.
[0036] 8. No need to select strain gauge orientation
[0037] The optical fiber of this invention is integrally cast and embedded in the substrate, avoiding the limitation of strain gauges with fixed ends that can only measure strain in a specific direction. Therefore, this invention eliminates the need to select a suitable strain gauge direction or perform corresponding calibration and correction in its application.
[0038] 9. High yield rate
[0039] The optical fiber of this invention is integrally cast and embedded in the substrate, which avoids the shortcomings of surface-mount adhesive bonding, such as glue leakage, poor sealing, and yield rate being limited by the bonding technique.
[0040] 10. Simple structure, small size, easy to process, easy to install, and low cost.
[0041] This utility model includes an optical fiber, a substrate, and a packaging tube. The optical fiber is integrally formed in the substrate by casting. The exposed end of the optical fiber is sealed by the packaging tube. It has a simple structure, small size, easy processing, convenient installation, and low cost. Attached Figure Description
[0042] To more clearly illustrate the technical solutions in the embodiments of this utility model or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments recorded in this utility model. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.
[0043] Figure 1 This is a structural diagram of a fiber optic strain gauge according to Embodiment 1 of this utility model;
[0044] Figure 2This is a structural diagram of a fiber optic strain gauge according to Embodiment 2 of this utility model;
[0045] Figure 3 This is a side cross-sectional view of the packaging tube of a fiber optic strain gauge according to Embodiment 2 of this utility model;
[0046] Figure 4 This is a structural diagram of a fiber optic strain gauge according to Embodiment 3 of this utility model;
[0047] Figure 5 This is a side cross-sectional view of the packaging tube of a fiber optic strain gauge according to Embodiment 3 of this utility model;
[0048] Figure 6 This is a structural diagram of the inner wall mold used to make the serrated protrusions in Embodiment 2 of this utility model.
[0049] Explanation of key figure labels:
[0050] 1. Optical fiber; 2. Substrate; 3. Encapsulation tube; 301. Fusion bond; 4. Serrated protrusion; 5. Flexible epoxy resin filler layer. Detailed Implementation
[0051] To enable those skilled in the art to better understand the technical solutions of this utility model, the technical solutions of the embodiments of this utility model will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this utility model, and not all embodiments. Based on the embodiments of this utility model, all other embodiments obtained by those skilled in the art without creative effort should fall within the protection scope of this utility model.
[0052] Example 1:
[0053] like Figure 1 A fiber grating strain gauge is disclosed, comprising an optical fiber 1, a substrate 2, and a packaging tube 3, wherein:
[0054] Optical fiber 1 is integrally cast and embedded in substrate 2, forming a single integral structure with the substrate material. The exposed end of optical fiber 1 is sealed by a pair of encapsulation tubes 3. Specifically, one end of each pair of encapsulation tubes 3 is inserted into the interior of substrate 2. A fusion bonding portion 301 is formed between the encapsulation tubes 3 and substrate 2 by heating substrate 2. The fusion bonding portion 301 physically interlocks the encapsulation tubes 3 with substrate 2, forming an integrated sealed structure after cooling. The length of the fusion bonding portion 301 accounts for 1 / 3 to 1 / 5 of the total length of the encapsulation tubes 3 to ensure stability.
[0055] The substrate 2 is a fully sealed sheet structure with a thickness of 0.2 mm; the substrate 2 can be made of materials such as filled modified PTFE composite matrix.
[0056] The encapsulation tube 3 is made of fusible polytetrafluoroethylene and has an inner diameter of 0.12 mm. The fixing structure between the encapsulation tube 3 and the optical fiber 1 is as follows: the encapsulation tube 3 and the optical fiber 1 are fused together by heating and attached to the surface of the optical fiber 1, while the substrate 2 is heated at the same time, so that the encapsulation tube 3 and the substrate 2 form a physical interlock. After cooling, an integrated sealed structure is formed.
[0057] Example 2:
[0058] like Figures 2-3 A fiber grating strain gauge is disclosed, comprising an optical fiber 1, a substrate 2, and a packaging tube 3, wherein:
[0059] Optical fiber 1 is integrally cast and embedded in substrate 2, forming a single integral structure with the substrate material. The exposed end of optical fiber 1 is sealed by a pair of encapsulation tubes 3. Specifically, one end of each pair of encapsulation tubes 3 is inserted into the interior of substrate 2. A fusion bonding portion 301 is formed between the encapsulation tubes 3 and substrate 2 by heating substrate 2. The fusion bonding portion 301 physically interlocks the encapsulation tubes 3 with substrate 2, forming an integrated sealed structure after cooling. The length of the fusion bonding portion 301 accounts for 1 / 3 to 1 / 5 of the total length of the encapsulation tubes 3 to ensure stability.
[0060] The substrate 2 is a fully sealed structure with a thickness of 1 mm. The substrate 2 can be made of materials such as filled modified PTFE composite material.
[0061] Encapsulation tube 3 is made of fusible polytetrafluoroethylene (PTFE) and has an inner diameter of 1 mm. The fixing structure between the encapsulation tube 3 and the optical fiber 1 is as follows: the encapsulation tube 3 is fixed through an inner wall mold (such as...). Figure 6 The substrate 2 expands during high-temperature casting after the optical fiber 1 is inserted, which pushes the serrated protrusion 4 on the inner wall of the encapsulation tube 3 into the surface of the optical fiber 1. After cooling, the substrate 2 shrinks and the protrusion structure permanently clamps the optical fiber 1.
[0062] Example 3:
[0063] like Figures 4-5 A fiber grating strain gauge is disclosed, comprising an optical fiber 1, a substrate 2, and a packaging tube 3, wherein:
[0064] Optical fiber 1 is integrally cast and embedded in substrate 2, forming a single integral structure with the substrate material. The exposed end of optical fiber 1 is sealed by a pair of encapsulation tubes 3. Specifically, one end of each pair of encapsulation tubes 3 is inserted into the interior of substrate 2. A fusion bonding portion 301 is formed between the encapsulation tubes 3 and substrate 2 by heating substrate 2. The fusion bonding portion 301 physically interlocks the encapsulation tubes 3 with substrate 2, forming an integrated sealed structure after cooling. The length of the fusion bonding portion 301 accounts for 1 / 3 to 1 / 5 of the total length of the encapsulation tubes 3 to ensure stability.
[0065] The substrate 2 is a fully sealed structure with a thickness of 2mm. The substrate 2 can be made of materials such as filled modified PTFE composite material.
[0066] The encapsulation tube 3 is made of fusible polytetrafluoroethylene and has an inner diameter of 1.8 mm. The fixing structure between the encapsulation tube 3 and the optical fiber 1 is as follows: the encapsulation tube 3 forms a flexible buffer layer by injecting a flexible epoxy resin filling layer 5 into the gap between it and the optical fiber 1. The metal-free fixing is achieved by low-temperature curing. The outer encapsulation tube 3 is combined with the substrate 2 to provide high-temperature protection.
[0067] As a variation of Embodiments 1 to 3, the thickness of the substrate 2 is any value between 0.2 and 2.0 mm; and the inner diameter of the encapsulation tube 3 is any value between 0.12 and 1.8 mm.
[0068] The fabrication process of a fiber Bragg grating strain gauge according to this invention is as follows:
[0069] S1. Fabrication of substrate mold: Fabricate a substrate mold for casting substrate material, divide the substrate mold into at least one small square, and use the small square as the position for casting substrate material. Each small square is uniformly engraved with multiple long strip-shaped grooves for placing optical fiber 1.
[0070] S2. The exposed end of optical fiber 1 is encapsulated using encapsulation tube 3; there are three encapsulation methods:
[0071] ① The encapsulation tube 3 is heated to achieve fusion bonding with the optical fiber 1 and to adhere to the surface of the optical fiber. The substrate 2 is heated simultaneously, so that the encapsulation tube 3 and the substrate 2 form a physical interlock. After cooling, an integrated sealed structure is formed.
[0072] ②The encapsulation tube 3 is formed by the inner wall mold to form a sawtooth protrusion 4. After the optical fiber 1 is inserted, the substrate 2 expands during high temperature casting, pushing the protrusion of the encapsulation tube 3 into the surface of the optical fiber 1. After cooling, the substrate 2 shrinks, and the sawtooth protrusion 4 permanently clamps the optical fiber 1.
[0073] ③ The encapsulation tube 3 forms a flexible buffer layer by injecting flexible epoxy resin slurry into the gap with the optical fiber 1. It achieves metal-free fixation through low-temperature curing. The outer encapsulation tube 3 is combined with the substrate 2 to provide high-temperature protection.
[0074] S3. Casting substrate 2: Cast the substrate material and optical fiber 1 as a whole on the pre-made substrate mold, with one optical fiber 1 placed in each small groove.
[0075] Compared with existing technologies, the fiber optic strain gauge of this invention integrally casts the fiber optic cable 1 and the substrate 2, forming a single unit with superior overall performance, high strength, and resistance to damage or destruction from external forces. It also boasts a long service life and is less prone to detachment or displacement, resulting in more stable and reliable measurement results. Furthermore, it avoids the limitation of fixed-end strain gauges, which can only measure strain in specific directions. In application, there is no need to select a suitable strain gauge direction or perform corresponding calibration and correction. During use, fixing the substrate 2 to the object being measured is equivalent to directly fixing the fiber optic cable 1 to the object, ensuring complete contact between the strain gauge and the object, thus making the strain gauge measurement more accurate.
[0076] The exposed end of the fiber 1 of the fiber grating strain gauge of this invention is sealed by the encapsulation tube 3, so that the fiber is reliably fixed in the encapsulation tube. The encapsulation is simple and reliable, convenient to process, and low in cost.
[0077] It will be apparent to those skilled in the art that this invention is not limited to the details of the exemplary embodiments described above, and that it can be implemented in other specific forms without departing from the spirit or essential characteristics of this invention. Therefore, the embodiments should be considered illustrative and non-limiting in all respects, and the scope of this invention is defined by the appended claims rather than the foregoing description. Thus, it is intended that all variations falling within the meaning and scope of equivalents of the claims be included within this invention. No reference numerals in the claims should be construed as limiting the scope of the claims.
[0078] Furthermore, it should be understood that although this specification describes embodiments, not every embodiment contains only one independent technical solution. This narrative style is merely for clarity. Those skilled in the art should consider the specification as a whole, and the technical solutions in each embodiment can also be appropriately combined to form other embodiments that can be understood by those skilled in the art.
Claims
1. A fiber optic strain gauge, characterized in that, It includes an optical fiber, a substrate, and a pair of encapsulation tubes. The optical fiber is integrally embedded in the substrate by casting. The substrate has a fully sealed structure. Both ends of the optical fiber are exposed. The exposed ends of the optical fiber are sealed by a pair of encapsulation tubes. A fixing structure is provided between the optical fiber and the encapsulation tubes. One end of each of the two encapsulation tubes is inserted into the interior of the substrate, and a fusion bonding portion is provided between each of the two encapsulation tubes and the substrate. The length of the fusion bonding portion accounts for 1 / 3 to 1 / 5 of the total length of the encapsulation tube.
2. The fiber optic strain gauge according to claim 1, characterized in that, The fixed structure is formed directly by fusing the heated encapsulation tube with the optical fiber and bonding it to the surface of the optical fiber.
3. A fiber optic strain gauge according to claim 1, characterized in that, The fixing structure includes a protrusion structure disposed inside the encapsulation tube, which clamps the end of the optical fiber through the protrusion structure.
4. A fiber optic strain gauge according to claim 3, characterized in that, The protrusion structure includes multiple sets of serrated protrusions, which are circumferentially distributed on the inner wall of the encapsulation tube. These serrated protrusions are embedded in the surface of the optical fiber during high-temperature casting of the substrate.
5. A fiber optic strain gauge according to claim 4, characterized in that, The encapsulation tube is formed by molding multiple sets of serrated protrusions through an inner wall mold.
6. A fiber optic strain gauge according to claim 1, characterized in that, The fixing structure includes a flexible buffer layer disposed between the optical fiber and the encapsulation tube, and the flexible buffer layer is fixed to the end of the optical fiber by low-temperature curing.
7. A fiber optic strain gauge according to claim 6, characterized in that, The flexible buffer layer includes a flexible epoxy resin filler layer, which is formed by injecting flexible epoxy resin slurry and curing it at low temperature.
8. A fiber optic strain gauge according to claim 1, characterized in that, The thickness of the substrate is 0.2-2.0 mm.
9. A fiber optic strain gauge according to claim 1, characterized in that, The inner diameter of the encapsulation tube is 0.12-1.8 mm.
10. A fiber optic strain gauge according to claim 9, characterized in that, The encapsulation tube is a fusible polytetrafluoroethylene tube.