Socket-type end face lead-out device for fiber grating sensor embedded in structure and its preparation method and application

Abstract

The present invention relates to a socket-type end-face lead-out device for an embedded fiber optic Bragg grating sensor, and its preparation method and application. First, the fiber optic Bragg grating sensor is connected and fixed to the fiber optic ferrule, and then a positioning sleeve and an outer protective sleeve are sequentially put on the surface of the fiber optic ferrule to obtain an end-face lead-out kit. The fiber optic Bragg grating sensor and the end-face lead-out kit are placed together in a molding material for curing and molding. The end of the molded part pre-embedded with the end-face lead-out kit is trimmed and processed. Finally, the external optical fiber is connected and fixed to the fiber optic ferrule to form a docking plug, and the docking plug is inserted into the end-face lead-out kit of the molded part. The present invention uses the end-face lead-out kit and the docking plug to achieve reliable and convenient lead-out and connection of optical fibers. The wiring process is simple and efficient, which greatly improves the efficiency of optical fiber layout.

Description

Technical Field

[0001] The present invention relates to the technical field of composite materials and optical fiber monitoring, and in particular to a socket-type end face lead-out device of a structure-embedded optical fiber grating sensor, and a preparation method and application thereof. Background Art

[0002] Fiber optic sensors are widely used in structural health monitoring due to their lightweight, multi-point measurement capabilities using a single fiber, resistance to electromagnetic interference, corrosion resistance, and ease of embedding within structures. To monitor strain, temperature, and other data within large structures, fiber Bragg grating (FBG) sensors are often embedded within the structure, leveraging their compact size. Related technologies are described in Chinese patents CN107367523A, CN112519996A, and CN108759706A.

[0003] For embedded fiber Bragg grating (FBG) optical systems, the point where the fiber is pulled out from within the structure is most susceptible to fiber breakage and circuit interruption. The primary solution to this problem currently involves protecting the fiber extraction point during installation. Extensive research and experimentation has led to the conclusion that the most practical method for protecting the extraction point is to add a metal or non-metallic sleeve to the fiber extraction point and partially bury the sleeve within the structure, thereby achieving enhanced protection. Commonly used sleeves include polyimide tubing, Teflon heat shrink tubing, silicone rubber tubing, and metal steel tubing.

[0004] However, in the above fiber extraction protection methods, the sleeve and optical fiber are usually extracted from the end face of the object to be measured. In order to prevent the fiber matrix from breaking, the end face of the specimen cannot be trimmed. This is inconsistent with the preparation process requirements of most current structures and makes it difficult to meet the requirements of the structural dimensional tolerance. In addition, the above fiber extraction protection method has another difficult-to-overcome problem. That is, if the optical fiber breaks at the extraction position due to misoperation during the specimen processing, it is difficult to re-splice and cannot meet the requirements for continued structural health monitoring. This also increases the difficulty of implementing traditional fiber extraction protection measures. Summary of the Invention

[0005] One objective of the present invention is to provide a socket-type end-face extraction device for embedded fiber grating (FBG) sensors in a structure. The device comprises a structural body, a fiber grating (FBG) sensor, an end-face extraction kit, and a docking plug. The fiber grating (FBG) sensor is connected to the end-face extraction kit via optical fibers. The resulting assembly is pre-embedded in the structural body and cured. The docking plug plugs into the end-face extraction kit to achieve optical fiber connectivity and signal transmission.

[0006] Furthermore, the end face lead-out kit includes an optical fiber ferrule and at least one sleeve, the optical fiber connected to the fiber grating sensor is fixed in the optical fiber ferrule, and the sleeve is sleeved on the optical fiber ferrule and extends outward for a distance to form a plug-in cavity.

[0007] Furthermore, the number of the sleeves is two, including a positioning sleeve and an outer protective sleeve. The positioning sleeve is sleeved on the optical fiber ferrule, and the outer protective sleeve is sleeved on the positioning sleeve.

[0008] Furthermore, the cross section of the positioning sleeve is C-shaped. This structure facilitates smooth docking with the optical fiber ferrule and has a certain degree of deviation tolerance.

[0009] Furthermore, the length of the outer protective sleeve is greater than the length of the positioning sleeve and greater than the length of the optical fiber ferrule, and the diameter of the docking plug is less than the inner diameter of the positioning sleeve and less than the inner diameter of the outer protective sleeve.

[0010] Furthermore, the docking plug includes an external optical fiber and an optical fiber ferrule, and the external optical fiber is fixed in the optical fiber ferrule.

[0011] Furthermore, at least one layer of protective sleeve made of plastic or metal is provided on the surface of the optical fiber ferrule of the docking plug to protect the external optical fiber.

[0012] Furthermore, the material of the optical fiber ferrule, the positioning sleeve, and the outer protective sleeve is selected from at least one of ceramics, metals, and high-temperature resistant plastics.

[0013] Furthermore, the optical fiber or external optical fiber is specifically a single-mode optical fiber or a multi-mode optical fiber, preferably a single-mode optical fiber.

[0014] Furthermore, the fiber grating sensor is specifically at least one of a strain sensor, a temperature sensor, an acceleration sensor, a displacement sensor, a pressure sensor, a flow sensor, a liquid level sensor, and the like.

[0015] Furthermore, the structural body is specifically at least one of a carbon fiber reinforced composite plate, a glass fiber reinforced composite plate, a building reinforcement plate, and a cement-based composite material.

[0016] A second object of the present invention is to provide a method for preparing a socket-type end-face lead-out device of the above-mentioned embedded fiber grating sensor, the method comprising the following steps: (a) firstly connecting and fixing the fiber grating sensor to the fiber optic ferrule, then successively installing a positioning sleeve and an outer protective sleeve on the surface of the fiber optic ferrule and fixing them, thereby obtaining an end-face lead-out kit, wherein the fiber grating sensor and the end-face lead-out kit together constitute an embedded component; (b) placing the embedded component in a molding material for molding, and trimming the end of the molded part where the end-face lead-out kit is pre-embedded; (c) connecting an external optical fiber to the fiber optic ferrule and fixing them to form a docking plug, and then inserting the docking plug into the end-face lead-out kit of the molded part.

[0017] Furthermore, the material used for fixing in steps (a)-(c) is UV light curing resin.

[0018] Furthermore, after the trimming process in step (b), the end face lead-out kit is cleaned with an organic solvent (such as alcohol or acetone) and dried.

[0019] A third object of the present invention is to apply the socket-type end-face lead-out device of the fiber optic Bragg grating sensor embedded in the above structure to structural health monitoring.

[0020] The present invention proposes a new method for end-face lead-out of a fiber optic Bragg grating sensor embedded in a structure. The wiring of this solution is simple and convenient. It only requires pre-embedding the fiber optic Bragg grating sensor and the end-face lead-out kit in the composite material before curing and molding. After curing and molding, the edge trimming can be conveniently performed without damaging the optical fiber. Finally, it is only necessary to insert the docking plug into the plug cavity of the end-face lead-out kit.

[0021] Compared with the prior art, the present invention has the following advantages:

[0022] (1) The optical fiber connection method of the present invention is a socket-type connection, which facilitates the edge trimming of composite material structural parts without damaging the optical fiber or affecting the connectivity and transmission of optical fiber signals. In addition, the thickness of the edge trimming can be flexibly changed within a certain range, and the processing adaptability is good;

[0023] (2) The present invention changes the conventional design of ensuring the continuity of the optical fiber matrix in the traditional lead-out method, and overcomes the common shortcomings of such designs such as complex post-processing process and low survival rate;

[0024] (3) The optical fiber lead-out part is detachably connected with the end face lead-out kit and the docking plug. The optical fiber mother body is physically discontinuous at the end face lead-out part. This design eliminates the tedious operation of lead-out protection and greatly improves the efficiency of optical fiber layout.

[0025] (4) The socket-and-socket method is used for secondary connection of the optical path, which makes the wiring process simple and efficient. In addition, the multiple hollow tubes made of different materials mounted on the surface of the optical fiber improve the reliability and durability of the lead-out part. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 This is a schematic diagram of the connection between the fiber optic ferrule of the end face lead-out kit and the optical fiber;

[0027] Figure 2 This is a schematic diagram of installing a positioning sleeve on the optical fiber ferrule of the end face lead-out kit;

[0028] Figure 3 This is a schematic diagram of fitting an outer protective sleeve onto the positioning sleeve of the end face lead-out kit;

[0029] Figure 4 A schematic diagram of embedding the end face lead-out kit in the molding material;

[0030] Figure 5 This is a schematic diagram of the sample connection after trimming;

[0031] Figure 6 This is the connection effect diagram of the sample after trimming;

[0032] Figure 7 A photo of the end face of the actual product;

[0033] Figure 8 Photos of the end-face lead-out parts of the actual product;

[0034] Figure 9 The following are photos of the test results of the actual product. DETAILED DESCRIPTION

[0035] In order to enable those skilled in the art to fully understand the technical solutions and beneficial effects of the present invention, further description will be given below in conjunction with specific embodiments and drawings.

[0036] Example 1

[0037] like Figure 1-9 As shown in the figure, the process of leading the embedded fiber Bragg grating sensor from the end face of the carbon fiber composite plate using a new socket structure is as follows:

[0038] (1) Peel off the outer coating of one end of the fiber grating sensor pigtail and cut it, leaving a bare fiber length of 6-7 mm.

[0039] (2) Insert the cut optical fiber into the ceramic ferrule with the flat end face and fix it with light-curing resin at the lead-out end.

[0040] (3) Put the ceramic positioning sleeve on the ceramic ferrule to ensure that the end face of the ceramic ferrule (corresponding to Figure 2A depth of 6 mm is reserved (on the right side of the figure), and the ceramic positioning sleeve is bonded and fixed to the ceramic ferrule using light-curing resin.

[0041] (4) Insert the ceramic ferrule and ceramic positioning sleeve assembly into a stainless steel metal tube approximately 1 mm in diameter and 40 mm in length. Secure the metal tube to the ceramic ferrule using a light-curing resin to create an end-face lead-out assembly. Mark the location of the ceramic positioning sleeve and seal both ends of the metal tube with light-curing resin.

[0042] (5) During the carbon fiber prepreg laying process, the fiber grating sensor assembly encapsulated by the metal tube is embedded in the composite material, and the ceramic positioning sleeve end marked in step (4) (corresponding to Figure 4 The middle right end is about 2mm away from the later cutting position.

[0043] (6) The carbon fiber composite material of the above pre-buried optical fiber lead-out kit is solidified and formed, and the edge is cut after being taken out to expose the metal protection sleeve section of the optical fiber lead-out kit. At this time, the end of the ceramic positioning sleeve in the pre-buried end face lead-out kit (corresponding to Figure 4 The right end in the figure is 2 mm inside the cutting line.

[0044] (7) Referring to steps (1) and (2), the external optical fiber is fixedly connected to another ceramic ferrule, and a heat shrink tube is applied to the surface of the ceramic ferrule to obtain a docking plug.

[0045] (8) Insert the butt plug into the end face lead-out kit on one side of the carbon fiber composite plate, thus completing the socket-type end face lead-out of the embedded optical fiber.

[0046] With the help of the above lead-out method, the demodulation of the fiber Bragg grating signal embedded in the carbon fiber composite plate was successfully realized. The specific process is as follows: After connecting the fiber lead-out end to the FAZT-I4 Bragg grating demodulator, the reflection spectrum of the fiber Bragg grating sensor embedded in the sample and its central wavelength signal were successfully captured. The results are as follows: Figure 9 This result shows that the lead-out solution provided by the present invention can successfully achieve the end-face lead-out of the optical fiber signal.

Claims

1. A method for preparing a socket-type end-face lead-out device for an embedded fiber Bragg grating sensor, characterized in that The method comprises the following steps: (a) First, the fiber Bragg grating sensor is connected to the optical fiber ferrule and fixed. Then, a positioning sleeve and an outer protective sleeve are installed on the surface of the optical fiber ferrule and fixed. Thus, an end-face lead-out kit is obtained. The fiber Bragg grating sensor and the end-face lead-out kit together constitute an embedded component. (b) placing the embedded component in a molding material for molding, and after molding, trimming the end of the molded component where the end face lead-out sleeve is pre-embedded, and cleaning the end face lead-out sleeve with an organic solvent and drying it; (c) Connect the external optical fiber and the optical fiber ferrule and fix them to form a docking plug, and insert the docking plug into the end face lead-out kit of the molded part.

2. The method according to claim 1, wherein: The material used for fixing in steps (a)-(c) is UV light curing resin.

3. A device obtained by the method for preparing the socket-type end-face lead-out device for a structure-embedded fiber Bragg grating sensor according to any one of claims 1 to 2, characterized in that: The device includes a structural body, a fiber grating sensor, an end face lead-out kit, and a docking plug. The fiber grating sensor is connected to the end face lead-out kit via an optical fiber. The resulting assembly is pre-embedded in the structural body and cured into shape. After curing, the end of the molded part where the end face lead-out kit is pre-embedded is trimmed. The docking plug is plugged into the end face lead-out kit to achieve optical fiber connectivity and signal transmission. The end face lead-out kit includes an optical fiber ferrule and at least one sleeve, the optical fiber connected to the fiber grating sensor is fixed in the optical fiber ferrule, and the sleeve is sleeved on the optical fiber ferrule and extends outward for a distance to form a plug-in cavity; There are two sleeves, including a positioning sleeve and an outer protective sleeve, and the cross section of the positioning sleeve is C-shaped; the positioning sleeve is sleeved on the optical fiber ferrule, and the outer protective sleeve is sleeved on the positioning sleeve; The length of the outer protective sleeve is greater than the length of the positioning sleeve and greater than the length of the optical fiber ferrule, and the diameter of the docking plug is less than the inner diameter of the positioning sleeve and less than the inner diameter of the outer protective sleeve. The material of the optical fiber ferrule, positioning sleeve and outer protective sleeve is selected from at least one of ceramic, metal and high-temperature resistant plastic.

4. The device according to claim 3, wherein: The butt plug includes an external optical fiber and an optical fiber ferrule. The external optical fiber is fixed in the optical fiber ferrule. At least one layer of protective sleeve made of plastic or metal is provided on the surface of the optical fiber ferrule of the butt plug.

5. The device according to claim 3, wherein: The optical fiber or external optical fiber connected to the fiber Bragg grating sensor is specifically a single-mode optical fiber or a multi-mode optical fiber; the fiber Bragg grating sensor is specifically at least one of a strain sensor, a temperature sensor, an acceleration sensor, a displacement sensor, a pressure sensor, a flow sensor, and a liquid level sensor; the structural body is specifically at least one of a carbon fiber reinforced composite plate, a glass fiber reinforced composite plate, and a cement-based composite material.

6. Application of the socket-type end-face lead-out device of the structure-embedded fiber Bragg grating sensor according to any one of claims 3 to 5 in structural health monitoring.

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