A temperature-insensitive fiber grating stress sensor

Abstract

The utility model relates to the field of optical fiber sensing technology, concretely relates to a temperature-insensitive fiber grating stress sensor, including the shell sleeve, is equipped with the opening in the both sides of shell sleeve, is equipped with left loading plate, right loading plate in the outside of two openings, left loading plate is connected with left response device, right loading plate is connected with right response device, left response device includes the left slider fixed on left loading plate, and left grating fixing frame, is equipped with left grating and a plurality of left grating fixed blocks on left grating fixing frame, left slider and left grating fixing frame sliding connection, the temperature of this application is self -compensating, and the measurement precision is high, through adopting two fiber grating series connection, and utilize its wavelength shift difference to calculate, has eliminated the cross -sensitive influence of temperature change to the measurement result, makes the sensor still can keep very high measurement precision and long -term stability in the complex environment of temperature fluctuation, need not additional temperature compensation element or complex algorithm.

Description

Technical Field

[0001] This utility model relates to the field of fiber optic sensing technology, specifically to a temperature-insensitive fiber optic grating stress sensor. Background Technology

[0002] Stress sensors play a crucial role in energy exploration and mining, satellite navigation, industrial production, virtual reality, human posture analysis, automotive driving, and military navigation and guidance. Fiber Bragg grating (FBG) sensors, with their advantages of small size, resistance to electromagnetic interference, and ease of networking, have become the preferred solution for critical applications.

[0003] However, existing FBG stress sensors generally face the following technical bottlenecks in engineering practice:

[0004] The problem of temperature cross-sensitivity is prominent. The center wavelength of the FBG responds to both temperature and strain changes. In practical applications, ambient temperature fluctuations directly superimpose on the stress measurement results, leading to serious deviations. Traditional temperature compensation methods (such as introducing a reference grating) increase system complexity and cost, and their long-term stability in harsh environments is poor.

[0005] Limited sensing sensitivity and measurement accuracy mean that the strain response sensitivity of a single FBG is relatively fixed, making it difficult to meet the high-precision monitoring requirements of large structures for minute stress changes. Improving sensitivity often requires complex sensitivity enhancement structure design, which in turn brings new problems such as packaging difficulties and reduced reliability.

[0006] Lacking effective stress direction sensing capabilities, most commercial stress sensors can only acquire the magnitude of stress but cannot identify its direction of action. In many critical applications (such as wings, bridges, and tunnels), the vector information of stress (magnitude and direction) is crucial for a comprehensive assessment of structural health, and existing technologies have significant functional gaps.

[0007] On-site installation and long-term stability challenges: The complex environment of engineering sites means that the ease of installation, structural robustness, and long-term fatigue and corrosion resistance of sensors directly determine the availability and lifespan of the monitoring system. Some existing designs are insufficient in balancing high performance and engineering practicality.

[0008] Therefore, there is an urgent need in this field for a new type of stress sensor that can eliminate temperature interference, has high sensitivity, can measure stress direction, and is simple in structure and easy to install, in order to meet the increasingly stringent engineering monitoring requirements. Utility Model Content

[0009] To address the problems existing in the prior art, this utility model provides a temperature-insensitive fiber Bragg grating stress sensor, which solves the problem of deviation caused by temperature influence in existing fiber Bragg grating stress sensors.

[0010] To solve the above problems, the technical solution of this utility model is as follows: A temperature-sensitive fiber optic grating stress sensor includes a housing sleeve with openings on both sides. A left loading plate and a right loading plate are provided on the outside of the two openings. The left loading plate is connected to a left sensing device that passes through the opening and is located inside the housing sleeve. The right loading plate is connected to a right sensing device that passes through the opening on the other side and is located inside the housing sleeve.

[0011] Furthermore, the left sensing device includes a left slider fixedly mounted on the left loading plate and a left grating fixing frame disposed within the outer casing sleeve. The left grating fixing frame is provided with a left grating and a plurality of left grating fixing blocks, and the left slider is slidably connected to the left grating fixing frame.

[0012] Furthermore, a left slider is provided on one side of the left slider, and a groove adapted to the left slider is provided on the outer side of the left grating fixing frame.

[0013] Furthermore, the right sensing device includes a right slider fixedly mounted on the right loading plate and a right grating fixing frame disposed within the outer casing sleeve. The right grating fixing frame is provided with a right grating and a plurality of right grating fixing blocks, and the right slider is slidably connected to the right grating fixing frame.

[0014] Furthermore, a right slider is provided on one side of the right slider, and a groove adapted to the right slider is provided on the outside of the right grating fixing frame.

[0015] Furthermore, the left grating fixing frame is U-shaped, and the right grating fixing frame is T-shaped.

[0016] Furthermore, the left grating is disposed between the left grating fixing frame and the right grating fixing frame, the right grating is disposed above the right grating fixing frame, and the left grating and the right grating are connected in series via single-mode optical fiber.

[0017] Furthermore, a cable outlet is provided on one side of the outer casing sleeve, through which an armored optical cable for inputting and outputting optical signals is provided, which is connected to a single-mode optical fiber.

[0018] Furthermore, fasteners are provided on the outside of the left and right grating fixing brackets to fix them inside the outer casing sleeve.

[0019] Compared with the prior art, the present invention has the following beneficial effects:

[0020] 1. Temperature self-compensation and high measurement accuracy: By using two fiber gratings connected in series and using the difference in their wavelength drift for calculation, the cross-sensitivity of temperature changes to the measurement results is eliminated. This allows the sensor to maintain extremely high measurement accuracy and long-term stability in complex environments with temperature fluctuations, without the need for additional temperature compensation components or complex algorithms.

[0021] 2. Increased sensitivity and high resolution: The unique mechanical structure design ensures that when subjected to force, one grating is stretched while the other is compressed. This differential effect greatly improves the sensor's response sensitivity to force, significantly outperforming traditional single grating sensors. Combined with high-precision demodulation technology, the stress resolution can easily reach 0.1N, with a stress direction sensing capability of ±45°, enabling the capture of minute stress changes.

[0022] 3. Vector strain measurement provides richer information dimensions. The innovative slider-groove structure enables the sensor to not only measure the magnitude of stress but also accurately sense the direction of stress. This provides more comprehensive vector strain information for structural health monitoring and is of great significance for assessing structural safety under complex working conditions.

[0023] 4. The structure is compact and reliable, easy to install and maintain. The overall structure of the sensor is simple and highly integrated. The outer sleeve provides effective protection. The standardized stress loading fixing device and optical cable exit design make it very convenient for installation, wiring and long-term maintenance in the engineering site. Attached Figure Description

[0024] Figure 1 This is a schematic diagram of the internal structure of the outer sleeve of this utility model;

[0025] Figure 2 This is a schematic diagram of the outer sleeve of this utility model;

[0026] Figure 3 This is a schematic diagram of the slide groove of this utility model;

[0027] Figure 4 This is a schematic diagram of the left slider of this utility model;

[0028] Figure 5 This is a schematic diagram of the installation of the left slider of this utility model;

[0029] Figure 6 The experimental curves show how the center wavelengths of the two Bragg fiber gratings of this invention change with increasing applied stress.

[0030] Figure 7 The curves showing the wavelength difference between the two Bragg fiber gratings of this invention as a function of temperature are shown.

[0031] Figure 8 The sensor input-output curves change with different angles when stress is applied to the present invention at different angles.

[0032] In the diagram: 1. Outer sleeve; 2. Opening; 31. Left grating fixing bracket; 32. Right grating fixing bracket; 4. Outlet hole; 5. Slide groove; 61. Left grating; 62. Right grating; 7. Grating fixing block; 81. Left slider; 82. Right slider; 91. Left loading plate; 92. Right loading plate; 101. Left slider; 11. Fixing component. Detailed Implementation

[0033] like Figure 1-5 As shown, this utility model provides a temperature-sensitive fiber optic stress sensor, including a housing sleeve 1, with an opening 2 on each side of the housing sleeve 1. The housing sleeve 1 is mounted on an internal sensing structure by a fixing member 11. The internal sensing structure mainly includes a left sensing device and a right sensing device arranged symmetrically.

[0034] like Figure 1 As shown, the left sensing device includes a left grating fixing frame 31, a left slider 81, and a left loading plate 91. The left grating fixing frame 31 is preferably U-shaped and is fixed inside the outer casing sleeve 1 by a fixing member 11. Figure 3 , 4 As described in section 5, a groove 5 is machined on the outer side of the left grating fixing frame 31, and a left slider 101 is provided at one end of the left slider 81. The left slider 101 is slidably embedded in the groove 5 of the left grating fixing frame 31, realizing the sliding connection between the left slider 81 and the left grating fixing frame 31. The other end of the left slider 81 is fixedly connected to the left loading plate 91. The left loading plate 91 is located outside the opening 2 on the left side of the outer casing sleeve 1 and is exposed to the outside to receive stress applied from the outside.

[0035] Similarly, the right sensing device includes a right grating fixing frame 32, a right slider 82, and a right loading plate 92. The right grating fixing frame 32 is preferably in the shape of a "T" and is fixed inside the outer casing sleeve 1 by a fixing member 11. It is arranged opposite to the left grating fixing frame 31. The outer side of the right grating fixing frame 32 is also machined with a sliding groove. One end of the right slider 82 is provided with a right sliding head, which is slidably embedded in the sliding groove of the right grating fixing frame 32. The other end of the right slider 82 is fixedly connected to the right loading plate 92. The right loading plate 92 is located outside the opening 2 on the right side of the outer casing sleeve 1 and is exposed to the outside to receive stress applied by the outside.

[0036] Multiple sets of grating fixing blocks 7 are respectively provided on the left grating fixing frame 31 and the right grating fixing frame 32. The left grating 61 is fixed between the left grating fixing frame 31 and the right grating fixing frame 32 by the grating fixing blocks 7, and the right grating 62 is fixed above the right grating fixing frame 32 by the grating fixing blocks 7. The left grating 61 and the right grating 62 are Bragg fiber gratings (FBG) and are connected in series inside the sensor through a single-mode optical fiber 13.

[0037] like Figure 2As shown, a cable outlet 4 is opened on one side of the outer casing sleeve 1. The other end of the series-connected optical fiber passes through the cable outlet 4 through the optical fiber fixing component, and the optical signal is transmitted to the external demodulation equipment by the armored optical cable 14.

[0038] When external stress F is applied to the sensor through the left and right loading plates (91, 92), the force is transmitted to the left and right grating holders (31, 32) through the left and right sliders (81, 82). Due to the unique structural design, one grating holder (e.g., the left grating holder 31) is subjected to a force that stretches it, while the other grating holder (e.g., the right grating holder 32) is subjected to a force that compresses it, thereby causing the left grating 61 and the right grating 62 fixed thereon to undergo tensile and compressive deformations, respectively.

[0039] The specific analysis method is as follows:

[0040] The basic expression for the FBG reflection wavelength is:

[0041] λ b =2n eff Λ(1)

[0042] Where, λ b n is the center wavelength of the grating eff Let Λ be the effective refractive index of the grating, and Λ be the period of the grating, such as... Figure 6 As shown, the performance test curves of the fiber Bragg grating strain sensor of this application are experimental curves showing the change of the center wavelength of the two Bragg fiber gratings as the applied stress increases. The square curve in the figure represents the drift curve of the left grating 61, and the circular curve represents the drift curve of the right grating 62.

[0043] The center wavelength variation of a Bragg fiber grating is influenced by both its period and effective refractive index. Under external stress, the fiber grating is stretched or compressed, thus altering its period Λ. Furthermore, due to the photoelastic effect, the effective refractive index of the grating also changes with external stress. When a Bragg fiber grating is subjected to the combined effects of external temperature and stress, its center wavelength shifts by Δλ. b It can be represented as:

[0044] Δλ b =2Δn eff，温度 Λ+2n eff ΔΛ 温度 +2Δn eff，应力 Λ+2n eff ΔΛ 应力 (2)

[0045] Among them, ΔΛ 温度 ΔΛ 应力 These are the effects of temperature or stress on the period Λ of the grating. These represent the thermo-optical effect caused by temperature or the elasto-optical effect caused by stress, respectively, affecting the effective refractive index n. eff The impact.

[0046] When the sensor's main body is subjected to stress, the two gratings are subjected to compressive and tensile forces respectively. The temperature-dependent drift on the center wavelengths of both gratings is identical. Therefore, by calculating the difference in the drift of the center wavelengths of the two gratings, the influence of temperature on their center wavelength drift can be eliminated. This yields the center wavelength difference Δλ between the two gratings. 总 for:

[0047] Δλ 总 =4Δn eff，应力 Λ+4n eff ΔΛ 应力 (3)

[0048] As can be seen, the sensor's stress sensitivity is increased to twice that of a single grating, and the cross-sensitivity of temperature is effectively eliminated, giving the sensor temperature-insensitive characteristics, such as... Figure 7 As shown in the figure, the performance test curve of the fiber optic strain sensor of this application is a curve of the wavelength difference between the two gratings changing with temperature. The horizontal triangle curve in the figure represents the final output temperature compensation effect of the sensor, which means that the sensor is not sensitive to temperature. The oblique square curve is actually the curve of the two gratings changing with temperature, which is completely redrawn on one side.

[0049] It is known that when a Bragg fiber grating is subjected to axial stress, the drift of the center wavelength of the sensor grating changes linearly with the axial stress, which can be expressed as the following equation:

[0050] Δλ 总 =k i ΔF+c i (4)

[0051] Where, k i c is the linear coefficient of the sensor grating wavelength difference as a function of stress. i ΔF is a constant, and ΔF is the stress variation value.

[0052] When the stress direction changes, the slider connected to the sensor in the groove on the outside of the main force-bearing body will change position accordingly. For example, if the stress direction rotates counterclockwise by an angle θ from the horizontal direction, the slider will slide up and down to the equilibrium position respectively. The force at this time is a vector, which can be expressed as follows:

[0053] Δλ 总 =k i ΔF(θ)+c i (5)

[0054] At this point, ΔF(θ) is a quantity related to the stress direction. Through experiments, the magnitude and direction of the stress in the sensor can be calibrated, thereby obtaining a series of specific expressions (5) corresponding to specific stress and direction conditions, and thus obtaining the sensing performance of the strain sensor, such as Figure 8 As shown in the figure, the performance test curve of the fiber optic strain sensor of this application is a curve showing how the sensor input and output curves change with different angles when stress is applied at different angles. Different graphs in the figure represent the output curves corresponding to different angles, which means that the sensor can distinguish the stress conditions at different angles.

[0055] Based on a grating resolution of 1 pm, it can be calculated that the stress resolution of this sensor can reach ±0.1N, and the stress direction angle ratio can reach ±1°.

[0056] The above specific embodiments are only used to illustrate the technical solution of this utility model and are not intended to limit it. Although this utility model has been described in detail with reference to examples, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solution of this utility model without departing from the scope of the technical solution of this utility model, and all such modifications or substitutions should be covered within the scope of the claims of this utility model.

Claims

1. A temperature-sensitive fiber optic stress sensor, comprising a housing sleeve (1), with openings (2) on both sides of the housing sleeve (1), characterized in that: A left loading plate (91) and a right loading plate (92) are provided on the outside of the two openings (2). The left loading plate (91) is connected to a left sensing device that passes through the opening (2) and is located inside the outer casing sleeve (1). The right loading plate (92) is connected to a right sensing device that passes through the other side opening (2) and is located inside the outer casing sleeve (1).

2. The temperature-sensitive fiber optic grating stress sensor according to claim 1, characterized in that: The left sensing device includes a left slider (81) fixed on the left loading plate (91) and a left grating fixing frame (31) inside the outer casing sleeve (1). The left grating fixing frame (31) is provided with a left grating (61) and a number of grating fixing blocks (7). The left slider (81) is slidably connected to the left grating fixing frame (31).

3. The temperature-sensitive fiber optic stress sensor according to claim 2, characterized in that: The left slider (81) has a left slider head (101) on one side, and the left grating fixing frame (31) has a groove (5) on the outside that is adapted to the left slider head (101).

4. The temperature-sensitive fiber optic stress sensor according to claim 3, characterized in that: The right sensing device includes a right slider (82) fixed on the right loading plate (92) and a right grating fixing frame (32) located inside the outer sleeve (1). The right grating fixing frame (32) is provided with a right grating (62) and a plurality of grating fixing blocks (7). The right slider (82) is slidably connected to the right grating fixing frame (32).

5. A temperature-sensitive fiber optic stress sensor according to claim 4, characterized in that: The right slider (82) has a right slider head on one side, and the right grating fixing frame (32) has a groove on the outside that is adapted to the right slider head.

6. A temperature-sensitive fiber optic grating stress sensor according to claim 5, characterized in that: The left grating holder (31) is U-shaped, and the right grating holder (32) is T-shaped.

7. A temperature-sensitive fiber Bragg grating stress sensor according to claim 6, characterized in that: The left grating (61) is located between the left grating fixture (31) and the right grating fixture (32), and the right grating (62) is located above the right grating fixture (32). The left grating (61) and the right grating (62) are connected in series by a single-mode optical fiber (13).

8. A temperature-sensitive fiber optic stress sensor according to claim 7, characterized in that: A cable outlet (4) is provided on one side of the outer casing sleeve (1), and an armored optical cable (14) for inputting and outputting optical signals is provided through the cable outlet (4) and connected to the single-mode optical fiber (13).

9. A temperature-sensitive fiber optic grating stress sensor according to claim 8, characterized in that: On the outside of the left grating holder (31) and the right grating holder (32), there are fasteners (11) that fix them in the outer casing sleeve (1).

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