Fiber bragg grating low-frequency vibration sensor

Abstract

A fiber bragg grating low-frequency vibration sensor is characterized in that the end part of a cross rod of an L-shaped base is connected with a first mass block through a first flexible hinge, the upper surface of the first mass block is connected with a second mass block through a second flexible hinge, and a certain distance is formed between the second mass block and the end part of a vertical rod of the L-shaped base; the upper surface of the second mass block is flush with the upper surface of the end part of the vertical rod of the L-shaped base, optical fibers are adhered to the upper surface of the end part of the vertical rod of the L-shaped base and the upper surface of the second mass block through glue, and a grating is inscribed on an optical fiber section between the vertical rod of the L-shaped base and the second mass block. Through the synergistic effect of the two stages of mass blocks and the flexible hinges, a multi-stage vibration amplification transmission path is formed, the overall bending rigidity of the structure is effectively reduced, low-frequency vibration signals can be accurately captured, and the sensitivity is remarkably improved.

Description

Technical Field

[0001] This invention belongs to the field of earthquake service technology, and specifically relates to a fiber optic grating low-frequency vibration sensor. Background Technology

[0002] Fiber Bragg grating sensing is based on the linear drift characteristics of Bragg wavelength with strain and temperature. With its significant advantages such as strong anti-electromagnetic interference capability, distributed multiplexing capability, high measurement accuracy, and strong environmental adaptability, it has been widely used in many fields such as structural health monitoring, seismic detection, and oil and gas exploration.

[0003] In technical solutions for detecting FBG vibration signals, classic sensing structures mainly include single-layer cantilever beam structures, symmetrical double-beam structures, and piezoelectric elastic structures. However, these traditional structures generally suffer from the following common technical defects: First, the high single-stage bending stiffness results in a small strain output, making it difficult to accurately capture weak vibration signals; second, the structural design has stringent requirements for processing precision, and the assembly process is complex, which is not conducive to large-scale production and application; third, in low-frequency vibration signal detection scenarios, the problem of insufficient mechanical gain is particularly prominent, severely limiting the detection sensitivity of the sensing structure.

[0004] In existing technologies, Chen Y, Li X, Xia W, et al. proposed a cantilever-hinge FBG accelerometer structure in "Design and experimental validation of an FBG accelerometer using Cantilever-Hinge structures" (Optical Fiber Technology, 2025, 91: 104156), attempting to achieve low-frequency vibration signal detection through structural optimization. However, the results show that the sensing sensitivity of this cantilever-hinge structure can only reach 54.12 pm / g. Furthermore, in order to reduce the mechanical stiffness and resonant frequency of the structure to meet the requirements of low-frequency vibration detection, a more complex structural design was adopted, which not only further increased the difficulty of processing and assembly but also led to a significant increase in manufacturing costs, failing to fundamentally solve the technical problems existing in traditional FBG vibration sensing structures. Summary of the Invention

[0005] The technical problem to be solved by the present invention is to overcome the shortcomings of the prior art and provide a fiber optic grating low-frequency vibration sensor that is simple to construct, highly sensitive, and can significantly amplify low-frequency weak vibration signals.

[0006] The technical solution adopted to solve the above technical problems is: a fiber optic grating low-frequency vibration sensor, wherein the end of the crossbar of the L-shaped base is connected to a first mass block through a first flexible hinge, the upper surface of the first mass block is connected to a second mass block through a second flexible hinge, the second mass block is spaced a certain distance from the end of the vertical rod of the L-shaped base, the upper surface of the second mass block is flush with the upper surface of the end of the vertical rod of the L-shaped base, optical fibers are glued to the upper surface of the end of the vertical rod of the L-shaped base and the upper surface of the second mass block, and a grating is engraved on the optical fiber segment located between the vertical rod of the L-shaped base and the second mass block.

[0007] As a preferred technical solution, the horizontal distance between the first flexible hinge and the second flexible hinge is 5 to 10 mm.

[0008] As a preferred technical solution, the first flexible hinge has an arc shape on the side near the vertical rod of the L-shaped base and a flat surface on the opposite side, and the second flexible hinge has the same structure as the first flexible hinge.

[0009] As a preferred technical solution, the arc diameter of the first flexible hinge is 5 to 8 mm, and the minimum thickness is 0.5 to 1 mm.

[0010] As a preferred technical solution, the first mass block is the same as the second mass block.

[0011] As a preferred technical solution, the grating has a grating region length of 3 to 8 mm and a center wavelength of 1530 to 1560 nm.

[0012] As a preferred technical solution, the sensitivity of the sensor for:

[0013]

[0014] In the formula, It is the effective elastic coefficient. It is the mass of the mass block. It is the center wavelength of the grating. It is the cross-sectional area of ​​the optical fiber. It is the elastic modulus of the optical fiber. It is the stiffness coefficient of the elastic structure. This represents the effective length of the optical fiber.

[0015] The beneficial effects of this invention are as follows:

[0016] This invention forms a multi-stage vibration amplification and transmission path through the synergistic effect of two-stage mass blocks and flexible hinges, effectively reducing the overall bending stiffness of the structure, accurately capturing low-frequency vibration signals, and significantly improving sensitivity, with the highest sensitivity reaching 102.88 pm / g.

[0017] The present invention also features a simple structure, small size, and the ability to be deployed in an array. Attached Figure Description

[0018] Figure 1 This is a schematic diagram of the structure of a fiber optic grating low-frequency vibration sensor according to the present invention.

[0019] Figure 2 This is the sensitivity test curve at 0.5Hz.

[0020] Figure 3 It is a sensitivity test curve of 5-50Hz.

[0021] Figure 4 It is a dynamic response graph of different accelerations at a frequency of 40Hz.

[0022] L-shaped base 1, first flexible hinge 2, first mass block 3, second flexible hinge 4, second mass block 5, grating 6. Detailed Implementation

[0023] The present invention will be further described in detail below with reference to the accompanying drawings and embodiments, but the present invention is not limited to the following embodiments.

[0024] Example 1

[0025] exist Figure 1 In this embodiment, an L-shaped base 1 of a fiber optic grating low-frequency vibration sensor has a first mass block 3 connected to the end of its horizontal bar via a first flexible hinge 2. A second mass block 5 is connected to the upper surface of the first mass block 3 via a second flexible hinge 4. The second mass block 5 is spaced a certain distance from the end of the vertical bar of the L-shaped base 1. The upper surface of the second mass block 5 is flush with the upper surface of the end of the vertical bar of the L-shaped base 1. Optical fibers are glued to the upper surface of the end of the vertical bar of the L-shaped base 1 and the upper surface of the second mass block 5. A grating 6 is engraved on the optical fiber segment between the vertical bar of the L-shaped base 1 and the second mass block 5. The grating 6 has a grating area length of 5 mm and a center wavelength of 1540 nm. The horizontal distance between the first flexible hinge 2 and the second flexible hinge 4 is 8 mm. The side of the first flexible hinge 2 closest to the vertical bar of the L-shaped base 1 is arc-shaped, and the opposite side is flat. The arc diameter of the first flexible hinge 2 is 7 mm, and the minimum thickness is 0.8 mm. The second flexible hinge 4 has the same structure as the first flexible hinge 2.

[0026] Among them, the sensitivity of the sensor for:

[0027]

[0028] In the formula, It is the effective elastic coefficient. It is the mass of the mass block. It is the center wavelength of grating 6. It is the cross-sectional area of ​​the optical fiber. It is the elastic modulus of the optical fiber. It is the stiffness coefficient of the elastic structure. This represents the effective length of the optical fiber.

[0029] The working principle is as follows:

[0030] When low-frequency vibrations act on the sensor's environment, the L-shaped base remains stationary. The vibration excitation is indirectly transmitted through the base to the elastic system composed of the first mass block 3, the second mass block 5, the first flexible hinge 2, and the second flexible hinge 4. Under inertia, the first mass block 3 displaces along the vibration direction. The initial transmission of vibration is achieved through the elastic deformation of the first flexible hinge 2. The displacement of the first mass block 3 is transmitted to the second mass block 5 through the second flexible hinge 4, creating a two-stage vibration amplification effect. The amplified vibration displacement of the second mass block 5 directly acts on the optical fiber attached to it. When the second mass block 5 moves away from or towards the vertical rod of the base, it causes the grating 6 on the optical fiber to be stretched or compressed, thereby achieving a regular change in the grating pitch. By detecting the drift of the center wavelength of the grating 6 using an optical fiber demodulation device, the amplitude, frequency, and other key parameters of the low-frequency vibration can be deduced, enabling accurate detection of weak low-frequency vibration signals.

[0031] Example 2

[0032] In this embodiment, the horizontal distance between the first flexible hinge 2 and the second flexible hinge 4 is 5mm, the arc diameter of the first flexible hinge 2 is 5mm, the minimum thickness is 0.5mm, the grating 6 has a grating area length of 3mm and a center wavelength of 1530nm. Other components and their connection relationships are the same as in Embodiment 1.

[0033] Example 3

[0034] In this embodiment, the horizontal distance between the first flexible hinge 2 and the second flexible hinge 4 is 8mm, the arc diameter of the first flexible hinge 2 is 5mm, the minimum thickness is 0.5mm, the grating 6 has a grating area length of 5mm and a center wavelength of 1550nm. Other components and their connection relationships are the same as in Embodiment 1.

[0035] experiment:

[0036] To verify the beneficial effects of the present invention, the inventors adopted the technical solution of Example 1 and conducted sensitivity tests.

[0037] For low-frequency vibrations of 0.5 Hz, an acceleration of 0.036–0.18 g was applied in steps of 0.036 g, and the wavelength shift was recorded. The data are as follows: Figure 2As shown, after fitting, the sensitivity is 90.3 pm / g. Then, points from 5 to 50 Hz were selected, and the acceleration was set to 0.2g as the starting point, with a step size of 0.2g, stopping at 1g. The drift data of the center wavelength was recorded, and the data was plotted as shown below. Figure 3 As shown, the average sensitivity is 102.88 pm / g. Figure 4 As can be seen from the data, the center wavelength change of the fiber optic grating under accelerations of 0.2 g, 0.4 g, 0.6 g, 0.8 g and 1.0 g are all smooth sine waves, thus demonstrating that the present invention can stably detect vibration signals with different accelerations within the working frequency range.

Claims

1. A fiber Bragg grating low-frequency vibration sensor, characterized in that: The end of the crossbar of the L-shaped base is connected to a first mass block via a first flexible hinge. The upper surface of the first mass block is connected to a second mass block via a second flexible hinge. The second mass block is spaced a certain distance from the end of the vertical bar of the L-shaped base. The upper surface of the second mass block is flush with the upper surface of the end of the vertical bar of the L-shaped base. Optical fibers are glued to the upper surface of the end of the vertical bar of the L-shaped base and the upper surface of the second mass block. A grating is engraved on the optical fiber segment located between the vertical bar of the L-shaped base and the second mass block.

2. The fiber Bragg grating low-frequency vibration sensor according to claim 1, characterized in that: The horizontal distance between the first flexible hinge and the second flexible hinge is 5 to 10 mm.

3. The fiber optic grating low-frequency vibration sensor according to claim 1 or 2, characterized in that: The first flexible hinge has an arc shape on one side near the vertical rod of the L-shaped base and a flat surface on the other side. The second flexible hinge has the same structure as the first flexible hinge.

4. The fiber Bragg grating low-frequency vibration sensor according to claim 3, characterized in that: The first flexible hinge has an arc diameter of 5 to 8 mm and a minimum thickness of 0.5 to 1 mm.

5. The fiber Bragg grating low-frequency vibration sensor according to claim 1, characterized in that: The first mass block is the same as the second mass block.

6. The fiber Bragg grating low-frequency vibration sensor according to claim 1, characterized in that: The grating has a grating area length of 3–8 mm and a center wavelength of 1530–1560 nm.

7. The fiber Bragg grating low-frequency vibration sensor according to claim 1, characterized in that: The sensitivity of the sensor for: In the formula, It is the effective elastic coefficient. It is the mass of the mass block. It is the center wavelength of the grating. It is the cross-sectional area of ​​the optical fiber. It is the elastic modulus of the optical fiber. It is the stiffness coefficient of the elastic structure. This represents the effective length of the optical fiber.

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