Self-temperature-compensation flexible fiber bragg grating strain rosette based on glass solder packaging

Abstract

The invention discloses a self-temperature-compensation flexible fiber bragg grating strain rosette based on glass solder packaging, and belongs to the technical field of optical fiber sensing. The strain rosette comprises a flexible polyimide (PI) substrate, the substrate is of a Y-shaped structure with three arms forming an included angle of 120 degrees, a sensitization window is arranged in the middle of each arm, and a strain isolation island is arranged in the center of each arm; the single sensing optical fibers are arranged in series in a non-crossed loop path in the substrate, and sequentially pass through the measuring grating in each window and the temperature compensation grating in the isolation island; the optical fiber sensing sections are solidified at the two ends of the window through glass solder. According to the invention, the problem of creep deformation of organic glue is solved by using the inorganic characteristic of glass solder, the cross stress of the optical fiber is eliminated and the packaging thickness is reduced through the full built-in loopback routing, and high-precision and in-situ self-temperature-compensation measurement in a high-temperature and complex strain environment can be realized.

Description

Technical Field

[0001] This invention relates to the field of fiber optic sensing and structural health monitoring technology, and in particular to a self-temperature compensated flexible fiber Bragg grating strain gauge based on glass solder encapsulation. Background Technology

[0002] In fields such as aerospace and power equipment, there is a need for real-time monitoring of the principal strain of complex surfaces. Traditional fiber optic grating (FBG) strain gauges are typically encapsulated using organic adhesives. However, at high temperatures, organic materials are prone to viscoelastic creep and hysteresis, leading to decreased measurement accuracy and zero-point drift.

[0003] Furthermore, FBG sensors exhibit cross-sensitivity to both temperature and strain. Existing technologies often employ a method of additionally attaching temperature sensors to the outside of the strain gauge, which results in a spatial thermal gradient between the temperature compensation point and the actual measurement point, leading to compensation errors under unsteady thermal conditions.

[0004] In terms of physical wiring, traditional routing methods are prone to fiber optic crossing and overlapping at the center of the substrate, which not only increases the sensor's package thickness but also causes localized stress concentration. Therefore, developing a novel strain gauge with high stability, in-situ temperature compensation, and optimized structure is of great significance. Summary of the Invention

[0005] The purpose of this invention is to provide a self-temperature-compensated flexible fiber Bragg grating strain roser based on glass solder encapsulation, which aims to solve the technical problems of traditional fiber bragg gratings such as easy creep of the encapsulation material under high temperature environment, measurement errors caused by inconsistent temperature compensation space, and thickness increase and stress concentration caused by fiber cross wiring.

[0006] To achieve the above objectives, the present invention adopts the following technical solution: A self-temperature compensated flexible fiber Bragg grating strain rose based on glass solder encapsulation includes a star-shaped polyimide flexible substrate (10), the substrate including three measuring arms at 120° angles to each other, the measuring arms being provided with sensitivity-enhancing windows (11, 12, 13); it also includes a sensing link composed of a single optical fiber, the link being connected in series with three measuring gratings (21, 23, 22) and a temperature compensated reference grating (24) located at the geometric center island (14) of the substrate; the optical fiber is arranged inside the substrate through a non-intersecting loop path, and the measuring grating is anchored to the substrate through glass solder curing points (30).

[0007] The temperature-compensated reference grating (24) adopts a single-end anchoring structure to achieve mechanical decoupling, and it is located in the central strain isolation island (14) formed by the substrate cut; the input end and output end of the optical fiber are located on the same side of the top of the substrate, and the glass solder curing point (30) is an inorganic material.

[0008] Compared with the prior art, the present invention has the following advantages: Significantly improved high-temperature stability of packaging: By using a combination of polyimide substrate and inorganic glass solder, a fully inorganic curing system was constructed, which completely eliminated the viscoelastic creep and strain hysteresis phenomena of traditional organic adhesives at high temperatures.

[0009] High-precision in-situ self-temperature compensation is achieved: by setting a physically isolated temperature compensation island at the geometric center of the substrate and using a single-end anchoring process, the temperature compensation grating and the measurement grating are ensured to be in the same instantaneous thermal field and completely isolated from mechanical strain, thus eliminating the compensation error caused by the spatial temperature gradient.

[0010] The physical structure was optimized and the sensitivity was improved: the design of the sensitivity-enhancing window cut off the redundant path of local mechanical transmission, so that the strain was concentrated in the grating area; the specific U-shaped loop routing realized the single-fiber plane cross-free traversal, which greatly reduced the packaging thickness and eliminated the stress concentration and micro-bending loss caused by fiber crossing.

[0011] Enhanced engineering practicality and reliability: The same-side entry and exit line design simplifies on-site wiring, reduces the risk of damage to fiber optic outlets in complex environments, and improves system integration. Attached Figure Description

[0012] Figure 1 is a planar structural diagram of the self-temperature compensated flexible fiber optic strain roser based on glass solder encapsulation according to the present invention. Figure 2 is a partial cross-sectional view of the present invention installed on the structure under test. Explanation of reference numerals in the attached figures

[0013] 10-Polyimide substrate; 11-First enhancement window; 12-Second enhancement window; 13-Third enhancement window; 14-Central strain isolation island; 20 - Fiber optic input; 25 - Fiber optic output; 21-First measuring grating; 22-Second measuring grating; 23-Third measuring grating; 24-Temperature compensation reference grating; 30 - Glass solder hardening point; 40 - Install adhesive layer; 50 - Structure under test. Detailed Implementation

[0014] The present invention will be further described below with reference to the accompanying drawings and embodiments.

[0015] Structure and wiring design: like Figure 1As shown, substrate 10 is made of a 50 μm thick polyimide film. The first, second, and third measurement gratings (21, 22, 23) are arranged along the three axes of the strain rosette. A corresponding sensitization window (11, 12, 13) is provided below each grating region. The sensing fiber enters vertically into the top arm from the input end 20, passes through the first measurement grating 21, and then smoothly arcs towards the lower left of the second measurement arm inside the substrate. At the end of this arm, it makes a U-shaped turn and passes through the second measurement grating 22 (sensing from the outside in). Subsequently, the fiber crosses the central region of the substrate and enters the lower right of the third measurement arm, passes through the third measurement grating 23 (sensing from the inside out), and makes a large-radius arc turn at the end of this arm. Finally, the fiber returns to the central island 14, connects to the vertically arranged temperature-compensated reference grating 24, and exits upwards from the output end 25. This path ensures that the fiber does not cross or overlap throughout its entire path within a single plane.

[0016] Packaging process: Low-melting-point glass paste is coated at both ends of each measuring grating. A laser beam is used for local scanning, melting and cooling the paste to form solidified points 30. Glass solder rigidly anchors the grating to the PI substrate. Considering the high sintering temperature of the glass solder, the grating used in this invention is preferably a femtosecond laser-written grating or a regenerated grating to ensure the spectral stability and long-term reliability of the grating region during high-temperature processing, perfectly matching the high-temperature processing characteristics of the glass solder. The temperature-compensated reference grating 24 is solidified only at one end, ensuring it is in a free-stretching state, does not bear the mechanical strain transmitted by the substrate, and only senses the temperature change at the center point.

[0017] Install application: like Figure 2 As shown, during installation, the bottom surface of the substrate 10 is integrally bonded to the surface of the structure under test 50 using a high-temperature resistant mounting adhesive layer 40. When the structure 50 experiences strain, the deformation is transmitted through the substrate to the sensitizing window area. Since there is no substrate constraint at the window, the strain is concentrated on the grating, causing a wavelength shift. By subtracting the wavelength shift of the temperature-compensated grating 24, the true strain value can be decoupled.

Claims

1. A self-temperature-compensated flexible fiber Bragg grating strain roser based on glass solder encapsulation, characterized in that, include: Flexible substrate (10): Made of polyimide material, it has a three-arm star structure with an included angle of 120° between adjacent measuring arms; Sensitization structure: The first sensitization window (11), the second sensitization window (12) and the third sensitization window (13) respectively penetrate the middle of the three measuring arms to generate local strain concentration; Central strain isolation island (14): Located at the geometric center of the flexible substrate (10), it is mechanically decoupled from the measuring arm through a slit structure; Fiber optic sensing link: includes a single sensing fiber, which is introduced from the fiber input end (20) at the top of the substrate, and sequentially passes through the first measurement grating (21), the second measurement grating (22), the third measurement grating (23) and the temperature compensation reference grating (24) at the center position, and is led out from the fiber output end (25); Solidification structure: Both ends of the measuring gratings (21, 22, 23) are anchored to both sides of the sensitizing window through glass solder solidification points (30); the temperature compensation reference grating (24) is arranged vertically in the central strain isolation island (14) and is anchored at one end through glass solder solidification points (30).

2. The self-temperature compensated flexible fiber optic strain gauge based on glass solder encapsulation according to claim 1, characterized in that: The sensing optical fiber is integrated in a planar layout inside the flexible substrate (10), and a large-radius U-shaped loop path for reversal is provided at the end of the measuring arm. The entire path is located within the physical boundary of the flexible substrate (10).

3. The self-temperature compensated flexible fiber optic strain gauge based on glass solder encapsulation according to claim 1, characterized in that: The fiber input end (20) and the fiber output end (25) are both located at the end of the measuring arm at the top of the flexible substrate (10) and are arranged in parallel and symmetrical order.

4. The self-temperature compensated flexible fiber optic strain gauge based on glass solder encapsulation according to claim 1, characterized in that: The glass solder curing point (30) is formed by laser local sintering of an inorganic glass slurry with a softening point between 320°C and 450°C.

5. The self-temperature compensated flexible fiber optic strain gauge based on glass solder encapsulation according to claim 1, characterized in that: The thickness of the flexible substrate (10) is 25 μm to 125 μm.

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