Fiber grating vibration sensor based on s-shaped elastomers and wedge-shaped sensitization beams

Abstract

A fiber grating vibration sensor based on S-shaped elastomers and wedge-shaped sensitization beams. The fiber grating vibration sensor comprises a fixed base (1) and two counterweight mass blocks (4) symmetrically arranged on the fixed base (1) one in front of the other, wherein S-shaped elastomers (31) are symmetrically provided above and below each counterweight mass block (4), and tail ends of two S-shaped elastomers (31) in the same horizontal direction are connected to each other; a wedge-shaped sensitization beam (32) is provided between each S-shaped elastomer (31) and the counterweight mass block (4), and the wedge-shaped sensitization beams (32) are used for amplifying the vibration amplitudes of the counterweight mass blocks (4); and a dual-fiber grating string (7) is provided between the two counterweight mass blocks (4), one end of the dual-fiber grating string (7) passing through the fixed base (1) and then being connected to a sealing end (9) and an armored optical fiber cable (11), and the other end thereof being arranged inside the fixed base (1). Picking-up of ultra-low-frequency vibration signals is achieved, and the sensitivity is relatively high.

Description

A fiber Bragg grating vibration sensor based on an S-shaped elastic body and a sensitive wedge beam Technical Field

[0001] The invention belongs to the field of fiber grating sensors, and in particular relates to a fiber grating vibration sensor based on an S-shaped elastic body and a sensitivity-enhancing wedge beam. Background Art

[0002] Vibration is present in all aspects of production and life, including large structures like bridges, high-rise buildings, and mines; vehicles like airplanes, high-speed trains, and ships; and various large-scale instruments and equipment. Abnormal vibration in these structures often indicates structural health issues. Low-frequency vibration monitoring plays a crucial role in vibration monitoring. For example, a large hydroelectric generator operates at approximately 60 rpm (1 Hz). The vibration caused by water vortexes is approximately one-third of the rotational speed, or about 0.3 Hz. Highway and railway bridges with a typical span of 30 to 60 meters have a natural frequency of approximately 2 Hz. A high-rise building reaching 400 meters has a natural frequency of 0.16 Hz. The first-order natural frequency of a heavier gravity dam is around 3 Hz, while that of a lighter arch dam is around 1.5 Hz. Therefore, real-time online monitoring of key load-bearing components of large-scale projects is essential through a series of testing and analysis methods.

[0003] In low-frequency vibration sensing and monitoring applications, fiber Bragg grating (FBG) sensors offer advantages over traditional electromagnetic sensors, including simple structure, high stability, high precision, wide dynamic range, and resistance to electromagnetic interference. Fiber Bragg grating (FBG) sensors can utilize wavelength division multiplexing technology to form a fiber-optic sensing network. Connecting to FBG demodulation equipment enables wide-range, long-distance status monitoring of diverse signals.

[0004] Research on low-frequency fiber Bragg grating (FBG) vibration sensors currently focuses on enhancing the sensitivity of low-frequency vibration signal pickup through different elastic structures and material packaging. Elastic structures primarily include embedded, cantilever, and mandrel spring oscillator types. Fiber Bragg grating (FBG) vibration sensors based on these structures each have their own advantages and disadvantages. Embedded structures have a high resonant frequency and low sensitivity, making them difficult to measure low-frequency, weak vibration signals. The cantilever beam type has a simple structure and has become a classic elastic element for low-frequency vibration fiber Bragg grating sensors. Hollow beam, double cantilever, and U-shaped beam structures have also emerged. However, because the sensitive grating is directly glued to the cantilever beam surface, chirping or multiple peaks can easily occur, resulting in inaccurate testing, low sensitivity, and poor stability. While the mandrel spring oscillator structure can achieve low-frequency vibration signal pickup, it is complex, difficult to package, and susceptible to lateral interference. Based on the design concept of the main vibration elastic element, domestic and foreign experts have conducted extensive and in-depth research on the design of low-frequency vibration fiber Bragg grating sensors. Flexible hinge fiber Bragg grating vibration sensors have also emerged. Zhang Faye designed an FBG accelerometer based on a flexible hinge structure with a response frequency of 10 to 240 Hz and a sensitivity of 236 pm / g, but it lacks temperature compensation. Current vibration sensors mainly measure frequencies above 10 Hz, but sensors that can pick up signals below 10 Hz or even at ultra-low frequencies are rare. Therefore, the development of low-frequency fiber Bragg grating vibration sensors with high sensitivity, ultra-low frequency vibration feedback, a wide response frequency range, strong lateral interference resistance, and temperature compensation has become a major focus of low-frequency fiber Bragg grating vibration sensor design.

[0005] Summary of the Invention

[0006] Purpose of the invention: The purpose of the present invention is to provide a fiber Bragg grating vibration sensor based on an S-shaped elastomer and a sensitive wedge beam, which can realize the pickup of ultra-low frequency vibration signals with high sensitivity.

[0007] Technical solution: The fiber optic Bragg grating vibration sensor based on an S-shaped elastomer and a sensitivity-enhancing wedge beam of the present invention includes a fixed base, two groups of counterweight mass blocks symmetrically arranged on the fixed base in front and back, S-shaped elastomers symmetrically arranged above and below each counterweight mass block, and the ends of the two S-shaped elastomers in the same horizontal direction are connected; a sensitivity-enhancing wedge beam is arranged between each of the S-shaped elastomers and the counterweight mass block, and the sensitivity-enhancing wedge beam is used to amplify the vibration amplitude of the counterweight mass block; a dual fiber optic Bragg grating string is arranged between the two counterweight mass blocks, one end of the dual fiber optic Bragg grating string passes through the fixed base and is connected to the sealed and armored optical cable, and the other end is arranged inside the fixed base.

[0008] Furthermore, the fixed base, S-shaped elastomer, and sensitive wedge beam are made of the same elastic alloy material by wire cutting, so the elastic sensitive component has no other associated components, which reduces redundant errors and improves the stability of the sensor.

[0009] Furthermore, all the S-shaped elastomers and all the sensitive wedge-shaped beams on the fixed base constitute the vibration elastic system of the sensor. The elastic coefficient K of the vibration elastic system has a direct influence on the sensitivity S and the natural resonance frequency f0 of the sensor, and the elastic coefficient K of the vibration elastic system is determined by the elastic modulus E of its material, the structural parameters of the S-shaped elastomer and the sensitive wedge-shaped beam.

[0010] Furthermore, the elastic coefficient K of the vibration elastic system, the sensitivity S of the sensor, and the natural resonance frequency f0 are calculated as follows:

[0011] Where L is the length of the S-shaped elastic body; t is the height of the S-shaped elastic body; b is the width of the cross section of the S-shaped elastic body; h is the thickness of the cross section of the S-shaped elastic body; n is the number of elastic units; W is the length of the wedge beam; m is the total mass of the central component of the fixed base and all the counterweight blocks; λ B is the wavelength of the Bragg grating; L, t, b, h, n, and W are obtained by optimizing the parameters according to the sensitivity S and the natural resonance frequency f0.

[0012] Furthermore, the counterweight mass block is made of hard alloy material and is fixedly connected to the central component of the fixed base by fixing screws to form a vibration mass block.

[0013] Furthermore, the dual fiber Bragg grating string is inscribed on one optical fiber and arranged in a vertically symmetrical package. The wavelength of the inscribed dual fiber Bragg grating string is between 1525 and 1565 nm, and the wavelength difference between the two gratings inscribed on both sides of the dual fiber Bragg grating string exceeds 5 nm.

[0014] Furthermore, a first groove and a second groove distributed vertically are provided in the middle of the fixed base, and the two gratings of the dual fiber grating string are placed in the first groove and the second groove respectively.

[0015] Furthermore, a third groove, a fourth groove and a fifth groove are provided on the fixed base, and the bare fiber parts at both ends and the middle of the dual fiber grating string are respectively encapsulated in the third groove, the fifth groove and the fourth groove of the fixed base by optical glue.

[0016] Furthermore, the mounting surface of the fixed base is processed with a threaded hole and is fixed to the sensor mounting surface by a reducing adapter screw.

[0017] Furthermore, a groove is formed between the vibrating mass block and the fixed base, so that an elastic buffer area exists when the vibrating mass block and the optical fiber deform and move up and down, thereby causing the vibrating mass block to have a large vertical displacement, and also ensuring that the optical fiber will not be broken when the sensor is subjected to a large vibration shock.

[0018] The technical solution of the present invention utilizes a vibration response system composed of symmetrically distributed S-shaped elastic bodies, a sensitivity-enhancing wedge-shaped beam, and a vibrating mass to pick up external excitations. Dual gratings serve as vibration-sensing sensitive elements. When the vibration response system is subjected to external excitation acceleration in the vertical direction, the inertia of the vibrating mass applies tensile and compressive forces to the elastic components composed of the upper and lower symmetrical S-shaped elastic bodies and the wedge-shaped beam. Consequently, the upper and lower gratings are stretched and compressed, respectively, experiencing equal and opposite strains. The grating wavelengths shift in opposite directions, doubling the vibration sensitivity. This converts the external vibration signal into a wavelength-modulated signal of a fiber Bragg grating (FBG), which is then connected to a fiber Bragg grating demodulation device for demodulation.

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

[0020] (1) The S-shaped elastic structure that reduces the structural stiffness, the wedge-shaped beam that amplifies the vibration feedback, and the increase in the mass of the mass block are used to improve the vibration pickup sensitivity in many aspects, and the temperature compensation function is realized by using the double grating packaging method. As a result, the sensor has the advantages of high sensitivity, good ultra-low frequency vibration pickup capability, a wide response frequency band, stable signal output, strong lateral anti-interference ability, simple structure, and easy to realize multi-dimensional vibration measurement.

[0021] (2) The present invention reduces the structural elastic coefficient through the parametric design of the S-shaped elastic body, amplifies the vibration amplitude of the mass block through the wedge-shaped beam, and increases the vibration response mass to increase the vibration sensitivity, thereby realizing the pickup of ultra-low frequency vibration signals, with a sensitivity of about 840pm / g and a minimum vibration pickup frequency of 0.5Hz.

[0022] (3) The present invention uses the same elastic alloy material to integrally process the fixed base and the elastic structure. The elastic sensitive component has no other associated components, which reduces redundant errors and improves the stability of the sensor.

[0023] (4) There are grooves of a certain width between the S-shaped elastic structures, which creates an elastic buffer area between the vibrating mass block and the optical fiber, so that the vibrating mass block has a large vertical displacement, which also ensures that the optical fiber will not be broken when the sensor is subjected to a large vibration shock, thereby improving the reliability of the sensor.

[0024] (5) The present invention realizes temperature self-compensation through a dual grating structure. Since the dual gratings written on the same optical fiber are symmetrically packaged, the induced external vibration strain is exactly opposite and equal in amplitude, and the two packaged gratings are subjected to the same temperature environment. Therefore, the signal matching of the dual sensing gratings can eliminate the influence of temperature drift (the difference in the demodulated symmetrical grating wavelength signals) and increase the sensitivity multiplication, which can effectively improve the low-frequency vibration pickup capability of the sensor. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] FIG1 is a front view of a fiber Bragg grating vibration sensor according to the present invention;

[0026] FIG2 is a left side view of the fiber Bragg grating vibration sensor of the present invention;

[0027] FIG3 is a schematic structural diagram of an S-shaped elastic body (1 / 4 basic elastic unit) and a sensitive wedge beam according to the present invention;

[0028] FIG4 is a time domain response diagram of the fiber Bragg grating vibration sensor based on the S-shaped elastic body and the sensitive wedge beam of the present invention;

[0029] FIG5 is a linear response diagram of the fiber Bragg grating vibration sensor based on the S-shaped elastic body and the sensitive wedge beam of the present invention. DETAILED DESCRIPTION

[0030] The technical solution of the present invention is described in detail below in conjunction with specific implementation methods and the accompanying drawings.

[0031] First, it should be noted that the directions mentioned in the present invention, such as front-back, left-right, up-down, horizontal, vertical, and so on, are defined relative to the directions in the respective drawings. They are relative concepts and can therefore vary depending on the position and application conditions. Therefore, these or other directions should not be understood as restrictive terms.

[0032] As shown in Figures 1-2, the fiber Bragg grating vibration sensor based on an S-shaped elastomer and a sensitive wedge beam of the present invention comprises a fixed base 1, a set screw 2, an S-shaped elastomer 31, a sensitive wedge beam 32, a counterweight mass 4, a fixing screw 5, a central component 6, a dual fiber Bragg grating string 7, an elastic buffer region 8, an end cap 9, a plastic sleeve 10, an armored optical cable 11, a first groove 12, a second groove 13, a third groove 14, a fourth groove 15, a fifth groove 16, and a vibration mass 17. The fixed base 1, the S-shaped elastomer 31, the sensitive wedge beam 32, and the central component 6 are made of the same elastic alloy material by wire cutting. There are four counterweight masses 4, which are symmetrically arranged front-to-back on the horizontal center line of the fixed base 1. In this embodiment, the counterweight masses 4 are fixed to the threaded holes machined in the center of the fixed base 1 by fixing screws 5. Each counterweight mass 4 is symmetrically positioned above and below a wire-cut S-shaped elastic body 31. The ends of two S-shaped elastic bodies 31 on the same horizontal axis are connected. A sensitivity-enhancing wedge beam 32 is positioned between each S-shaped elastic body 31 and the counterweight mass 4. The two vertical sensitivity-enhancing wedge beams 32 are symmetrical, and the two horizontal sensitivity-enhancing wedge beams 32 are also symmetrical. The two horizontal S-shaped elastic bodies 31 are also symmetrical. The four counterweight masses 4, located on the left and right sides and front and back, are positioned between the upper and lower S-shaped elastic bodies 31.

[0033] The mounting surface of the fixed base 1 is processed with a threaded hole, and the sensor needs to be fixed to the mounting surface through a reducing adapter screw. The reducing adapter screw is an adapter accessory with external threads at both ends. The sizes of the external threads at both ends are inconsistent. The thread size of one end is consistent with the size of the threaded hole at the bottom of the sensor, and the thread at the other end is consistent with the threaded hole on the mounting surface.

[0034] A dual fiber grating string 7 is set between the two counterweight masses 4. The dual fiber grating string 7 is engraved on an optical fiber and is symmetrically packaged in an upper and lower manner. The wavelength is selected between 1525 and 1565 nm. The wavelength difference between the two gratings engraved on both sides of the dual fiber grating string 7 exceeds 5 nm. The first groove 12 and the second groove 13 are processed and formed in the middle of the fixed base 1. The first groove 12 and the second groove 13 are distributed vertically. The two gratings of the dual fiber grating string 7 are placed in the first groove 12 and the second groove 13 respectively. The third groove 14, the fourth groove 15, and the fifth groove 16 are also processed and formed on the fixed base 1. The two ends and the middle bare fiber part of the dual fiber grating string 7 are respectively encapsulated in the third groove 14, the fifth groove 16, and the fourth groove 15 of the fixed base 1 by optical glue. One end of the dual fiber grating string 7 passes through the fixed base 1 and is connected to the end cap 9 and the armored optical cable 11, and the other end is arranged inside the fixed base 1; specifically, the optical fiber at one end of the stretched and fixed dual fiber grating string 7 passes through the threaded hole of the fixed base 1, the end cap 9 and the armored optical cable 11 respectively, and the bare fiber glued at the other end is terminated in the groove 14 of the fixed base 1, and is tightened in the threaded hole on the mounting surface of the fixed base 1 by the set screw 2. One end of the end cap 9 is fixed in the threaded hole machined and formed on the upper surface of the fixed base 1, and the other end of the end cap 9 is fixed to the armored optical cable 11 by cold-pressed tube extrusion molding, and the plastic sleeve 10 passes through the armored optical cable 11 and is connected to the end cap 9 through sealing silicone.

[0035] All S-shaped elastic bodies 31 and all sensitive wedge-shaped beams 32 on fixed base 1 constitute the sensor's vibroelastic system. The elastic coefficient K of this vibroelastic system directly affects the sensor's sensitivity S and natural resonant frequency f0. This elastic coefficient K is primarily determined by the material's elastic modulus E and the structural parameters of the S-shaped elastic bodies 31 and sensitive wedge-shaped beams 32. Because the S-shaped elastic body 31 has a relatively symmetrical structure, a quarter of the basic unit is used for structural mechanics analysis, as shown in Figure 3. The energy method from material mechanics is used below to split this unit into two parts to analyze its displacement under a vertical upward force F applied along the axis of symmetry.

[0036] Part 1: M1(x)=Fx, N1(x)=0, 0≦x≦Lb;

[0037] Part 2: M2(x)=F(Lb / 2), N2(x)=F, 0≦x≦tb;

[0038] Then the total displacement δ of 1 / 4 basic unit of S-type elastic body is 1 / 4总 where A = bh, I = b3h / 12:

[0039] The total displacement of a basic unit under the action of axial force F is:

[0040] According to the linear elastic theory K = F / δ, the axial elastic coefficient K of the n basic units of the S-type elastic body is S for:

[0041] The sensitivity-enhancing wedge-shaped beam 32 is simplified to an isotropic cantilever beam with a constant cross-section, from which the elastic coefficient K of the end face of the wedge-shaped beam along the axial direction can be obtained: L for:

[0042] Then the axial elastic coefficient K of the sensor elastic system is 总 for:

[0043] According to the definition of acceleration sensor sensitivity, the sensor sensitivity S is the ratio of the change in the central wavelength of the fiber Bragg grating to the acceleration a, that is, S = Δλ / a, where Δλ is the change in the central wavelength of the sensing grating due to strain, which can be expressed as:

[0044] Δλ B =(1-P e )δ αx λ B (8)

[0045] Where P e is the effective elastic-optic coefficient, which is related to the elastic-optic effect of the optical fiber; δ αx is the strain on the fiber Bragg grating along the axial direction. αx Substituting =F / K and F=ma into S=Δλ / a, we can get the expression of the sensor's single-sided strain grating sensitivity S1:

[0046] According to the structural natural frequency formula, the resonant frequency f0 of the sensor can be obtained as:

[0047] Wherein, L represents the length of the S-shaped elastic body; t represents the height of the S-shaped elastic body; b represents the width of the cross section of the S-shaped elastic body; h represents the thickness of the cross section of the S-shaped elastic body; n represents the number of elastic units; W represents the length of the wedge beam; m represents the total mass of the central component of the fixed base and all the counterweight blocks; E is the elastic modulus of the structural material; the dual fiber Bragg grating string (7) is a Bragg grating, λ B is the wavelength of the Bragg grating; L, t, b, h, n, and W are obtained by optimizing the parameters according to the sensitivity S and the natural resonance frequency f0.

[0048] Referring to Figure 2 , the central component 6 is symmetrically machined with four rectangular grooves of a certain depth, front and back, left and right. Through-threaded holes are machined in the middle of the rectangular grooves on both sides. Four counterweights 4 are embedded in the rectangular grooves and fixed to the central component 6 via fixing screws 5 to form a vibration mass 17. The counterweights 4 are made of cemented carbide, which has a density of 14.7 g / cm³, which is heavier than the density of the fixed base substrate (8.0 g / cm³). As can be seen from Equation (10), the heavier the vibration mass 17, the higher the sensor sensitivity.

[0049] As shown in FIG1 , a groove of a certain width is formed between the vibration mass block 17 and the fixed base 1 so that an elastic buffer area 8 exists between the vibration mass block 17 and the optical fiber when they deform and move up and down. In this embodiment, the width of the groove is greater than three times the width b of the cross section of the S-shaped elastomer.

[0050] During the packaging process, the dual fiber grating string 7 needs to be clamped in a displacement fixture to apply a certain amount of tension. The bare fibers on both sides and in the middle of the dual grating are sealed in the grooves of the fixed base using optical adhesive. When the sensor vibrates due to external excitation, the center wavelengths of FBG1 and FBG2 change as follows:

[0051] In formulas (11) and (12), Δλ B1 , Δλ B2 ,λ B1 ,λ B2 are the center wavelength change and center wavelength of FBG1 and FBG2 respectively; P is the elastic-optic coefficient; α1 and α2 are the thermal expansion coefficients of FBG1 and FBG2 respectively; ξ1 and ξ2 are the thermo-optic coefficients of FBG1 and FBG2 respectively; ΔT is the temperature change value; ε1 and ε2 are the strains of FBG1 and FBG2 respectively.

[0052] Since the two Bragg gratings have the same temperature sensitivity coefficient, when the elastic body vibrates up and down, the strains of the two gratings are equal in magnitude and opposite in direction, that is, ε1 = -ε2 = ε. Therefore, by subtracting equation (11) from equation (12), we can get:

[0053] According to the vibration acceleration sensitivity formula S = Δλ / a, the wavelength difference of the dual fiber Bragg grating string is twice that of the single fiber Bragg grating. Therefore, the sensitivity of the vibration sensor using the dual fiber Bragg grating string will be doubled, and the influence of external temperature on the measurement results can be compensated.

[0054] In order to verify the beneficial effects of the present invention, an experimental study was conducted on a vibration test environment using a fiber Bragg grating vibration sensor based on an S-shaped elastic body and a sensitive wedge beam of the present invention. The experimental results are as follows:

[0055] The experimental instruments used are: standard vertical vibration table, ultra-low frequency vibration table motion tester, vibration calibration device measurement and control instrument, dynamic fiber Bragg grating demodulator.

[0056] 1. Sensitivity test

[0057] According to the operating procedures of the low-frequency standard vibration table system, the standard vibration table is controlled to apply an external excitation of 10 Hz and 1 g, so that the central wavelengths of the vibration gratings on both sides of the fiber Bragg grating vibration sensor based on the S-type elastomer and the sensitive wedge beam fixed on the surface of the vibration table drift, and the wavelength drift of the gratings on both sides is detected by a dynamic fiber Bragg grating demodulator. As shown in Figure 4, it is a vibration time-domain wavelength response diagram of the fiber Bragg grating vibration sensor based on the S-type elastomer and the sensitive wedge beam of this invention.

[0058] As can be seen from Figure 4, the waveform amplitudes of the gratings on both sides of the fiber Bragg grating vibration sensor based on the S-shaped elastomer and the sensitive wedge beam of the invention are equal when excited in the vertical direction, and are symmetrical up and down. The wavelength change of the grating on one side is 420pm / g, and the wavelength change of the grating on the other side is 419.5pm / g. According to formula (11), the sensitivity of the vibration sensor is twice the grating change, and the sensitivity of the vibration sensor is about 840pm / g.

[0059] 2. Amplitude-frequency response

[0060] According to the operating procedures of the low-frequency standard vibration table system, the standard vibration table is controlled to apply external excitations of the same amplitude but different frequencies. The excitation amplitude is set to 0.02g, and the excitation frequency is continuously adjusted within the range of 0.5, 1, 2, 4, 6, 8, 10, 20, 40, 60, and 80Hz, so that the center wavelengths of the vibrating gratings on both sides of the fiber Bragg grating vibration sensor based on the S-type elastomer and the sensitive wedge beam fixed on the surface of the vibration table drift. The wavelength drift of the gratings on both sides is detected using a dynamic fiber Bragg grating demodulator. Table 1 below shows the dynamic characteristic data of the fiber Bragg grating vibration sensor based on the S-type elastomer and the sensitive wedge beam of the invention at the same amplitude but different frequencies.

[0061] As can be seen from the above table, the fiber Bragg grating vibration sensor based on the S-shaped elastomer and the sensitive wedge beam of this invention has a relatively stable wavelength change under external excitation of the same amplitude but different frequencies. The lowest responsive operating frequency can reach 0.5Hz, and the highest responsive operating frequency can reach 80Hz, that is, the vibration response working range is 0.5Hz~80Hz, and the response flatness is <3dB.

[0062] 3. Linear characteristic response

[0063] According to the operating procedures of the low-frequency standard vibration table system, the standard vibration table is controlled to apply external excitations of the same frequency but different amplitudes. The excitation amplitude is set to 10 Hz, and the excitation amplitude is continuously adjusted within the range of 0.2, 0.4, 0.6, 0.8, and 1 g, so that the central wavelengths of the vibration gratings on both sides of the fiber Bragg grating vibration sensor based on the S-type elastomer and the sensitive wedge beam fixed on the surface of the vibration table drift, and the wavelength drift of the gratings on both sides is detected by a dynamic fiber Bragg grating demodulator. Figure 5 is a linear response diagram of the fiber Bragg grating vibration sensor based on the S-type elastomer and the sensitive wedge beam under external excitations of the same frequency but different amplitudes.

[0064] As can be seen from FIG5 , the linear response fitting curve of the vibration sensor is R2=0.9955, and the nonlinearity is 0.06%. It can be seen that the linear response of the fiber Bragg grating vibration sensor is good.

[0065] In summary, the technical solution of the present invention adopts a symmetrically packaged dual grating structure to sense the external vibration strain in the opposite direction with equal amplitude. The signal matching of the dual sensing grating can eliminate the influence of temperature drift and improve sensitivity, which can effectively improve the low-frequency vibration pickup capability of the sensor. The present invention can have a wide working response area, achieve high sensitivity and linearity, and eliminate the influence of temperature drift, realize low-frequency vibration pickup capability, and can be easily expanded to three-dimensional vibration sensing.

Claims

1. A fiber Bragg grating vibration sensor based on an S-shaped elastic body and a sensitive wedge beam, characterized in that: It comprises a fixed base (1), two groups of counterweight mass blocks (4) symmetrically arranged on the fixed base (1) in the front and rear directions, an S-shaped elastic body (31) symmetrically arranged above and below each counterweight mass block (4), and the ends of the two S-shaped elastic bodies (31) in the same horizontal direction are connected; A sensitivity-enhancing wedge-shaped beam (32) is arranged between each of the S-shaped elastic bodies (31) and the counterweight mass block (4), and the sensitivity-enhancing wedge-shaped beam (32) is used to amplify the vibration amplitude of the counterweight mass block (4); A dual fiber grating string (7) is arranged between the two counterweight mass blocks (4); one end of the dual fiber grating string (7) passes through the fixed base (1) and is then connected to the end cap (9) and the armored optical cable (11); and the other end of the dual fiber grating string (7) is arranged inside the fixed base (1).

2. The fiber Bragg grating vibration sensor based on an S-shaped elastic body and a sensitive wedge beam according to claim 1, characterized in that: The fixed base (1), the S-shaped elastic body (31), and the sensitivity-enhancing wedge-shaped beam (32) are made of the same elastic alloy material through wire cutting.

3. The fiber Bragg grating vibration sensor based on an S-shaped elastic body and a sensitive wedge beam according to claim 1, characterized in that: All the S-shaped elastic bodies (31) and all the sensitivity-enhancing wedge-shaped beams (32) on the fixed base (1) form a vibration elastic system of the sensor. The elastic coefficient K of the vibration elastic system has a direct influence on the sensitivity S and the natural resonance frequency f0 of the sensor, and the elastic coefficient K of the vibration elastic system is determined by the elastic modulus E of the material, the structural parameters of the S-shaped elastic body (31) and the sensitivity-enhancing wedge-shaped beam (32).

4. The fiber Bragg grating vibration sensor based on an S-shaped elastic body and a sensitive wedge beam according to claim 3, characterized in that: The calculation formulas of the elastic coefficient K of the vibration elastic system, the sensitivity S of the sensor and the natural resonance frequency f0 are as follows: Wherein, L represents the length of the S-shaped elastic body; t represents the height of the S-shaped elastic body; b represents the width of the cross section of the S-shaped elastic body; h represents the thickness of the cross section of the S-shaped elastic body; n represents the number of elastic units; W represents the length of the wedge beam; m represents the total mass of the central component of the fixed base and all the counterweight blocks; λ B is the wavelength of the Bragg grating; L, t, b, h, n, and W are obtained by optimizing the parameters according to the sensitivity S and the inherent resonance frequency f0.

5. The fiber Bragg grating vibration sensor based on an S-shaped elastic body and a sensitive wedge beam according to claim 1, characterized in that: The counterweight mass block (4) is made of hard alloy material and is fixedly connected to a central component (6) in a fixed base (1) via fixing screws (5) to form a vibration mass block (17).

6. The fiber Bragg grating vibration sensor based on an S-shaped elastic body and a sensitive wedge beam according to claim 1, characterized in that: The dual fiber grating string (7) is inscribed on an optical fiber and is arranged in a vertically symmetrical package. The wavelength of the inscribed dual fiber grating string (7) is between 1525 and 1565 nm, and the wavelength difference between the two gratings of the dual fiber grating string (7) exceeds 5 nm.

7. The fiber Bragg grating vibration sensor based on an S-shaped elastic body and a sensitive wedge beam according to claim 1, characterized in that: A first groove (12) and a second groove (13) distributed vertically are arranged in the middle of the fixed base (1), and two gratings of the dual-fiber grating string (7) are placed in the first groove (12) and the second groove (13) respectively.

8. The fiber Bragg grating vibration sensor based on an S-shaped elastic body and a sensitive wedge beam according to claim 7, characterized in that: The fixed base (1) is provided with a third groove (14), a fourth groove (15), and a fifth groove (16); the two ends and the middle bare fiber portion of the dual fiber grating string (7) are respectively encapsulated in the third groove (14), the fifth groove (16), and the fourth groove (15) of the fixed base (1) by optical glue.

9. The fiber Bragg grating vibration sensor based on an S-shaped elastic body and a sensitive wedge beam according to claim 1, characterized in that: The mounting surface of the fixed base (1) is processed with a threaded hole and is fixed to the sensor mounting surface by means of a reducing adapter screw.

10. The fiber Bragg grating vibration sensor based on an S-shaped elastic body and a sensitive wedge beam according to claim 5, characterized in that: A groove is formed between the vibration mass block (17) and the fixed base (1), so that an elastic buffer area (8) exists between the vibration mass block and the optical fiber when they deform and move up and down.

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