A high-sensitivity fiber grating acceleration sensor

Abstract

A kind of high-sensitivity fiber grating acceleration sensor, including pedestal, through fiber block, intermediate beam and mass block, the top of the through fiber block is provided with a fiber slot, the bottom of through fiber block is connected with the top of pedestal, the bottom of pedestal is fixedly connected with the object to be measured, the middle part of pedestal is fixedly connected with the tail end of intermediate beam, the free end of intermediate beam is fixedly connected with the middle part of mass block, the top of mass block is provided with a second fiber slot, one end of monitoring optical fiber is arranged in the second fiber slot, the other end of monitoring optical fiber extends to the outside of sensor after passing through the first fiber slot, the bottom of mass block is higher than the bottom of pedestal;The part between the first fiber slot and the second fiber slot on the monitoring optical fiber is the suspended optical fiber with fiber grating arranged thereon, and the fiber beam spacing is clamped between the suspended optical fiber arranged in parallel and the intermediate beam.This design is less affected by the mutual restriction of natural frequency and sensitivity, and there is less limitation in sensitivity improvement.

Description

TECHNICAL FIELD

[0001] The application relates to an optical fiber grating acceleration sensor and belongs to the technical field of mechanical vibration measurement. BACKGROUND

[0002] In recent years, China's economy and technology have developed rapidly, and various engineering and technical fields have made rapid progress. The demand for high-quality measurement and analysis of vibration signals of engineering structures is becoming increasingly urgent. When abnormal vibration occurs in engineering structures, it usually causes damage to the vibrating object and leads to varying degrees of economic loss, and in severe cases, it can even cause catastrophic safety accidents. Therefore, it is of great significance to monitor the vibration of engineering structures.

[0003] The sensors that pick up vibration signals are mostly electrical sensors. Although such sensors can meet the vibration measurement requirements of most engineering applications, they have poor anti-electromagnetic interference ability and stability in high-voltage strong electromagnetic environments, are not convenient for multi-point arrangement, are difficult to implement distributed network monitoring, and the metal structure of their shell may cause discharge, which can pose a dangerous hidden danger to engineering, such as in high-voltage strong electromagnetic engineering environments such as water turbines. The signals of electrical sensors are very susceptible to interference. As a new type of passive sensor, optical fiber grating has the advantages of high sensitivity, corrosion resistance, anti-electromagnetic interference, and easy networking, so it is increasingly used in signal monitoring in complex environments such as high voltage and strong electromagnetism in the prior art.

[0004] At present, in most engineering applications, the most commonly used optical fiber grating sensor for picking up one-dimensional vibration signals is a cantilever beam type acceleration sensor due to its simple structure. However, due to the mutual restriction of the natural frequency and the sensitivity of the sensor, there is a limitation in the improvement of the sensitivity, which makes it difficult to meet the existing monitoring requirements, especially the pickup of low-frequency vibration with a vibration frequency below 50 Hz, or even ultralow-frequency vibration. In the industrial field, many large rotating equipment, especially the structure of the hydroelectric generator set, first shows failure in low-frequency vibration signals, so extra attention should be paid to the pickup and analysis of low-frequency vibration signals.

[0005] The information disclosed in this BACKGROUND section is for the purpose of increasing the understanding of the general background of the application and is not admitted to be prior art against the present application. SUMMARY

[0006] The application aims to overcome the defects and problems in the prior art that the inherent frequency and the sensitivity are greatly influenced by each other and the sensitivity is greatly limited in improvement, and provide a high-sensitivity fiber grating acceleration sensor which is less influenced by the inherent frequency and the sensitivity and has less limitation in sensitivity improvement.

[0007] To achieve the above object, the technical solution of the application is: a high-sensitivity fiber grating acceleration sensor, comprising a base, a fiber passing block, an intermediate cross beam and a mass block, a first fiber slot is formed in the top of the fiber passing block, the bottom of the fiber passing block is connected with the top of the base, the bottom of the base is fixedly connected with a to-be-measured object, the middle part of the base is fixedly connected with the tail end of the intermediate cross beam, the free end of the intermediate cross beam is fixedly connected with the middle part of the mass block, a second fiber slot is formed in the top of the mass block, one end of a monitoring optical fiber is arranged in the second fiber slot, the other end of the monitoring optical fiber extends to the outside of the sensor after passing through the first fiber slot, and the bottom of the mass block is higher than the bottom of the base.

[0008] The part of the monitoring optical fiber located in the first fiber slot and the second fiber slot is connected with the first fiber slot and the second fiber slot, respectively, and the part of the monitoring optical fiber located between the first fiber slot and the second fiber slot is a suspended optical fiber, a fiber grating is arranged on the suspended optical fiber, and the suspended optical fiber and the intermediate cross beam are arranged in parallel.

[0009] The middle part of the base is connected with the tail end of the intermediate cross beam perpendicularly, and the free end of the intermediate cross beam is connected with the middle part of the mass block perpendicularly.

[0010] The width of the intermediate cross beam is ten times or more than ten times of the thickness of the intermediate cross beam.

[0011] The fiber passing block is a cuboid structure, one end of the fiber passing block is connected with the top of the base in a flush manner, the other end of the fiber passing block extends towards the mass block, the vertical projection of the other end of the fiber passing block is located on the intermediate cross beam, and the fiber passing block, the base and the intermediate cross beam jointly form a block-beam clamping cavity which is open in one direction towards the mass block.

[0012] The vertical projection of one end of the suspended optical fiber is located on the intermediate cross beam, and the vertical projection of the other end of the suspended optical fiber is located on the mass block.

[0013] The mass block is a T-shaped structure, comprising a narrow top block and a wide bottom block which are connected in a vertical manner, the side part of the wide bottom block near the top thereof is connected with the free end of the intermediate cross beam, the top of the wide bottom block is connected with the bottom of the narrow top block, and the top of the narrow top block is provided with the second fiber slot which is formed in a transverse manner.

[0014] The sensitivity s of the sensor is:

[0015]

[0016] Where Pe is the optical elastic coefficient of the optical fiber, and λ B λ is the center wavelength of the optical fiber, h is the thickness of the intermediate beam, d is the spacing between the beams, m is the mass of the mass block, L is the length of the intermediate beam, l1 and l2 are the distances between any two points on the suspended optical fiber and the tail end, E is the elastic modulus of the intermediate beam, and b is the width of the intermediate beam.

[0017] The sensor also includes a housing that encloses the base, fiber optic block, intermediate crossbeam, mass block, and fiber optic grating. The bottom of the base is fixedly connected to the inner side of the bottom plate of the housing, and the outer side of the bottom plate is fixedly connected to the object to be measured. The bottom of the mass block is suspended above the bottom plate of the housing, and the other end of the monitoring fiber passes through the first fiber channel and the housing in sequence before extending to the outside of the sensor.

[0018] A through-hole for fiber optic cable is provided on the left side plate of the housing. The other end of the monitoring optical fiber passes through the first fiber slot and the through-hole in sequence and extends to the outside of the sensor.

[0019] The base, fiber optic block, intermediate crossbeam, and mass block are an integrated structure, all made of 304 steel.

[0020] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0021] 1. This invention discloses a high-sensitivity fiber Bragg grating accelerometer, comprising a base, a fiber optic block, a central crossbeam, and a mass block. The top of the fiber optic block has a transversely penetrating first fiber slot, the bottom of the fiber optic block is connected to the top of the base, the middle of the base is fixedly connected to the tail end of the central crossbeam, the free end of the central crossbeam is fixedly connected to the middle of the mass block, and the top of the mass block has a transversely penetrating second fiber slot. The portion of the monitoring fiber located between the first and second fiber slots is a suspended fiber, on which a fiber Bragg grating is mounted. The suspended fibers arranged parallel to each other and the central crossbeam are spaced at a fiber beam spacing. In application, the bottom of the base is fixedly connected to the object being measured. When measuring the vibration of an object, the mass block, under the influence of inertia, undergoes displacement relative to the object being measured. This relative displacement causes deformation of the intermediate crossbeam and the suspended optical fiber. Compared with existing technologies, this invention separates the suspended optical fiber with a fiber Bragg grating from the intermediate crossbeam, thus isolating the deformation of the fiber Bragg grating from the influence of the intermediate crossbeam. This achieves the goal of preventing chirping effects from the fiber Bragg grating without affecting the sensor's inherent frequency. Furthermore, it introduces a new parameter, "fiber beam spacing," to adjust the sensor's sensitivity. Adjusting this parameter does not affect the sensor's inherent frequency, and its relationship with sensitivity improvement is roughly proportional, greatly reducing the limitations on sensitivity enhancement. Therefore, this invention is less affected by the interaction between inherent frequency and sensitivity, and also has fewer limitations in terms of sensitivity improvement.

[0022] 2. In the high-sensitivity fiber grating acceleration sensor, the sensitivity s of the sensor is obtained according to the following formula:

[0023]

[0024] wherein Pe is the photoelastic coefficient of the fiber, is the center wavelength of the fiber, h is the thickness of the intermediate beam, d is the value of the fiber-beam spacing, m is the mass of the mass block, L is the beam length of the intermediate beam, l1 and l2 are the distances between any two points on the suspended fiber and the tail end, E is the elastic modulus of the intermediate beam, and b is the width of the intermediate beam. As can be seen, when the remaining values are fixed or known, the overall sensitivity of the sensor can be improved by increasing the value of d, with less limitation and better improvement effect, which is beneficial to picking up lower frequency, such as low-frequency vibration below 50 Hz, or even ultra-low frequency vibration, and is very beneficial to monitoring the vibration signals of large rotating equipment, especially the structure of the hydroelectric generator set, thereby improving the fault diagnosis effect. Therefore, the present application not only has less limitation in sensitivity improvement, but also is beneficial to monitoring the low-frequency vibration signals in the structure of the hydroelectric generator set.

[0025] 3. In the high-sensitivity fiber grating acceleration sensor, an outer shell is additionally provided, which covers the base, the fiber passing block, the intermediate beam, the mass block and the fiber grating, the bottom of the base is fixedly connected to the inner side surface of the shell bottom plate in the outer shell, the outer side surface of the shell bottom plate is fixedly connected to the object to be measured, the bottom of the mass block is suspended above the shell bottom plate, and the other end of the monitoring fiber extends to the outside of the sensor in sequence through the No. 1 fiber groove and the outer shell. The provision of the outer shell not only protects the main components of the sensor, but also is preferably made of non-metallic material, which does not produce discharge phenomenon, avoids dangerous hidden troubles for engineering, and especially has better effect when the material is ceramic. Therefore, the present application has good protection effect and does not produce discharge phenomenon.

[0026] 4. In the high-sensitivity fiber grating acceleration sensor, the width of the intermediate beam is ten times or more than the thickness of the intermediate beam, which is beneficial to reducing the influence of lateral interference and further improving the overall sensitivity of the sensor. Therefore, the sensitivity of the present application is higher. BRIEF DESCRIPTION OF DRAWINGS

[0027] Figure 1 is a structural schematic diagram of the present application.

[0028] Figure 2 is a top view of the present application.

[0029] Figure 3 is a front view of the present application.

[0030] Figure 4 is a bottom view of the present application.

[0031] Figure 5 is a structural schematic diagram after adding a shell in the present application.

[0032] Figure 6 is a left view of Figure 5 .

[0033] Figure 7 is a time-domain waveform diagram of example 3 in the present application.

[0034] Figure 8 is a frequency spectrum diagram of example 3 in the present application.

[0035] Figure 9 is an experimental result schematic diagram of the natural frequency of example 4 in the present application.

[0036] Figure 10 is an experimental result schematic diagram of the sensitivity of example 5 in the present application.

[0037] Figure 11 is an experimental result schematic diagram of the transverse anti-interference of example 6 in the present application.

[0038] In the figure: base 1, base through hole 11, through fiber block 2, first fiber groove 21, through fiber through hole 22, intermediate cross beam 3, tail end 31, free end 32, block beam clamping cavity 33, mass block 4, second fiber groove 41, narrow top block 42, wide bottom block 43, monitoring optical fiber 5, suspended optical fiber 51, optical fiber grating 52, fiber beam spacing 53, shell 6, shell bottom plate 61, left side plate 62, fiber passing hole 63, limiting device 7. DETAILED DESCRIPTION

[0039] The present application is further described in detail below in conjunction with the accompanying drawings and specific embodiments.

[0040] Referring to Figure 1 — Figure 11 , a high-sensitivity fiber grating acceleration sensor, comprising a base 1, a through fiber block 2, an intermediate cross beam 3 and a mass block 4, the top of the through fiber block 2 is provided with a transversely penetrating first fiber groove 21, the bottom of the through fiber block 2 is connected with the top of the base 1, the bottom of the base 1 is fixedly connected with a to-be-measured object, the middle part of the base 1 is fixedly connected with the tail end 31 of the intermediate cross beam 3, the free end 32 of the intermediate cross beam 3 is fixedly connected with the middle part of the mass block 4, the top of the mass block 4 is provided with a transversely penetrating second fiber groove 41, one end of a monitoring optical fiber 5 is arranged in the second fiber groove 41, the other end of the monitoring optical fiber 5 extends to the outside of the sensor after passing through the first fiber groove 21, and the bottom of the mass block 4 is higher than the bottom of the base 1.

[0041] The part of the monitoring optical fiber 5 located in the first fiber groove 21 and the second fiber groove 41 is connected with the first fiber groove 21 and the second fiber groove 41 correspondingly, and the part of the monitoring optical fiber 5 located between the first fiber groove 21 and the second fiber groove 41 is a suspended optical fiber 51, and the suspended optical fiber 51 is provided with an optical fiber grating 52, and the suspended optical fiber 51 and the middle cross beam 3 are clamped with a fiber-beam spacing 53.

[0042] The middle part of the base 1 is connected with the tail end 31 of the middle cross beam 3 vertically, and the free end 32 of the middle cross beam 3 is connected with the middle part of the mass block 4 vertically.

[0043] The width of the middle cross beam 3 is ten times or more than ten times of the thickness of the middle cross beam 3.

[0044] The through-fiber block 2 is a cuboid structure, one end of the through-fiber block 2 is connected with the top of the base 1 flushly, the other end of the through-fiber block 2 extends to the direction close to the mass block 4, the vertical projection of the other end of the through-fiber block 2 is located on the middle cross beam 3, and the through-fiber block 2, the base 1 and the middle cross beam 3 together enclose a block-beam clamping cavity 33 which is unidirectionally opened to the mass block 4.

[0045] The vertical projection of one end of the suspended optical fiber 51 is located on the middle cross beam 3, and the vertical projection of the other end of the suspended optical fiber 51 is located on the mass block 4.

[0046] The mass block 4 is a T-shaped structure, including a narrow top block 42 and a wide bottom block 43 connected vertically, the side part of the wide bottom block 43 close to the top thereof is connected with the free end 32 of the middle cross beam 3, the top of the wide bottom block 43 is connected with the bottom of the narrow top block 42, and the top of the narrow top block 42 is provided with a second fiber groove 41 which is transversely and penetratively formed.

[0047] The sensitivity s of the sensor is:

[0048]

[0049] Wherein, Pe is the photoelastic coefficient of the optical fiber, λ B is the central wavelength of the optical fiber, h is the thickness of the middle cross beam 3, d is the value of the fiber-beam spacing 53, m is the mass of the mass block 4, L is the beam length of the middle cross beam 3, l1 and l2 are the distances between any two points of the suspended optical fiber 51 and the tail end 31, E is the elastic modulus of the middle cross beam 3, and b is the width of the middle cross beam 3.

[0050] The sensor further comprises a shell 6 covering the base 1, the through-fiber block 2, the intermediate cross beam 3, the mass block 4 and the fiber grating 52, the bottom of the base 1 is fixedly connected with the inner side of a shell bottom plate 61 in the shell 6, the outer side of the shell bottom plate 61 is fixedly connected with the object to be measured, the bottom of the mass block 4 is suspended above the shell bottom plate 61, and the other end of the monitoring optical fiber 5 extends to the outside of the sensor in sequence through the first fiber groove 21 and the shell 6.

[0051] The shell 6 is provided with a fiber-penetrating hole 63 penetrating through the left side plate 62, and the other end of the monitoring optical fiber 5 extends to the outside of the sensor in sequence through the first fiber groove 21 and the fiber-penetrating hole 63.

[0052] The base 1, the through-fiber block 2, the intermediate cross beam 3 and the mass block 4 are integrated (processed by integrated cutting to avoid the problem that the characteristics of the sensor are affected by installation errors), and are made of 304 steel.

[0053] The principle of the present application is described as follows:

[0054] The cantilever beam type acceleration sensor has two important indexes, namely the natural frequency and the sensitivity. Among them, the higher natural frequency can have a wider dynamic measurement range, and the higher sensitivity coefficient is conducive to measuring weak signals. However, it can be known from the calculation formula of the natural frequency and the sensitivity that the two indexes are mutually restricted, and this defect cannot be overcome. Therefore, the improvement of the sensitivity and the natural frequency are separated, so that the restriction can be overcome to the greatest extent. The present application is to suspend the fiber grating 52 above the intermediate cross beam 3 to improve the sensitivity without restriction.

[0055] In the ordinary cantilever beam type acceleration sensor, the fiber grating is attached to the surface of the cantilever beam. If the fiber grating is attached to the surface of the intermediate cross beam in the present application, the calculation formula of the sensitivity is as follows:

[0056]

[0057] Compared with the calculation formula of the sensitivity of the sensor in which the fiber grating is suspended in the present application (as follows):

[0058]

[0059] It can be seen that the sensitivity in the present application is equivalent to being amplified by (h+2d) / h times, so the desired sensitivity can be obtained by setting the height d of the suspension fixation (i.e. the value of the fiber beam spacing 53), and this sensitivity increasing parameter d does not appear in the calculation formula of the natural frequency f (as follows), so adding the parameter d will not affect the natural frequency of the sensor, so the purpose of improving the sensitivity of the sensor without changing the natural frequency is achieved.

[0060]

[0061] In this invention, a protruding limiting device 7 is provided below the mass block 4. If the outer shell 6 is present, the limiting device 7 is connected to the top surface of the shell bottom plate 61.

[0062] In this invention, the outer shell 6 is preferably made of a non-magnetic, high-temperature resistant non-metallic material, such as ceramic.

[0063] In this invention, a through hole 11 extending vertically is provided inside the base 1, and a fiber through hole 22 corresponding to the through hole 11 is provided inside the fiber through block 2. During assembly, bolts or similar fasteners are used to pass through the shell bottom plate 61, the through hole 11, and the fiber through hole 22 in sequence to fix the base 1 and the shell 6.

[0064] Example 1:

[0065] See Figure 1 — Figure 3 A high-sensitivity fiber Bragg grating accelerometer includes a base 1, a fiber optic block 2, a central crossbeam 3, and a mass block 4. The top of the fiber optic block 2 has a transversely penetrating fiber groove 21. The bottom of the fiber optic block 2 is connected to the top of the base 1. The bottom of the base 1 is fixedly connected to the object to be measured. The middle part of the base 1 is fixedly connected to the tail end 31 of the central crossbeam 3. The free end 32 of the central crossbeam 3 is fixedly connected to the middle part of the mass block 4. The top of the mass block 4 has a transversely penetrating fiber groove 41, in which one end of a monitoring optical fiber 5 is disposed, and the other end of the monitoring optical fiber 5... After passing through the first fiber slot 21, the fiber extends to the outside of the sensor and connects to the fiber optic demodulator or is connected in series with other sensors to form a sensor network. The bottom of the mass block 4 is set higher than the bottom of the base 1. The parts of the monitoring fiber 5 located in the first fiber slot 21 and the second fiber slot 41 are connected to the first fiber slot 21 and the second fiber slot 41 respectively. The part of the monitoring fiber 5 located between the first fiber slot 21 and the second fiber slot 41 is a suspended fiber 51. A fiber optic grating 52 is set on the suspended fiber 51. The suspended fiber 51 arranged vertically and the middle crossbeam 3 are sandwiched together to form a fiber beam spacing 53. Preferably, the middle part of the base 1 is perpendicularly connected to the tail end 31 of the middle crossbeam 3, and the free end 32 of the middle crossbeam 3 is perpendicularly connected to the middle part of the mass block 4.

[0066] Example 2:

[0067] The basic content is the same as in Example 1, except that:

[0068] See Figure 4 and Figure 5The sensor further comprises a shell 6 in which the base 1, the fiber block 2, the intermediate cross beam 3, the mass block 4 and the fiber Bragg grating 52 are covered, the bottom of the base 1 is fixedly connected with the inner side of a shell bottom plate 61 in the shell 6, the outer side of the shell bottom plate 61 is fixedly connected with the object to be measured, the bottom of the mass block 4 is suspended above the shell bottom plate 61, and the other end of the monitoring optical fiber 5 extends to the outside of the sensor in sequence through the first fiber groove 21 and the shell 6. A fiber passing hole 63 is formed in the left side plate 62 in the shell 6, and the other end of the monitoring optical fiber 5 extends to the outside of the sensor in sequence through the first fiber groove 21 and the fiber passing hole 63.

[0069] Example 3

[0070] The basic content is the same as that in Example 1, except that:

[0071] The excitation signal frequency is set to 40 Hz, and the amplitude is 5 m / s 2 The experiment is carried out.

[0072] Figure 7 is a time-domain waveform diagram of vibration obtained after the sensor responds, Figure 8 is a frequency spectrum diagram of vibration obtained after the sensor responds, and the experimental results show that:

[0073] The present application can pick up low-frequency vibration signals, especially frequencies below 50 Hz.

[0074] Example 4

[0075] The basic content is the same as that in Example 1, except that:

[0076] As shown in Figure 9 , the fixed vibration signal amplitude is 5 m / s 2 , a sweep frequency test is carried out, the sweep frequency range is 0-300 Hz, the step is 20 Hz, three repeated experiments are carried out, when approaching the natural frequency, the step is appropriately reduced, and the experimental results of the natural frequency of the sensor are obtained. The experimental results show that:

[0077] The natural frequency of the present application is 168 Hz, which is close to the theoretical value, and the amplitude-frequency response curve is relatively flat in the range of 0-100 Hz, so the working frequency range of the present application is below 100 Hz, the measurement range is relatively wide, and the flatness is good below 50 Hz, so the frequency range requirement of picking up low-frequency vibration signals can be met.

[0078] Example 5

[0079] The basic content is the same as that in Example 4, except that:

[0080] As shown in Figure 10As shown, the exciter frequency was adjusted to 20, 50, and 80 Hz, with the acceleration varying from 2 to 12 m / s². 2 Three sets of experiments were conducted, and the average value of three repeated experiments was taken for each set. The sensor sensitivity experimental results were obtained. The experimental results show that:

[0081] The sensitivity (slope) at 20Hz, 50Hz, and 80Hz is 16pm / m·s. -2 16.65 pm / m·s -2 18.96 pm / m·s -2 Therefore, the sensitivity of this invention can meet the requirement of high sensitivity in picking up vibration signals.

[0082] Example 6:

[0083] The basic content is the same as in Example 4, except that:

[0084] like Figure 11 As shown, the amplitude of the fixed vibration signal is 5 m / s. 2 The wavelength shift of the sensor was measured at a frequency of 40Hz in the principal axis direction and in the non-principal axis direction (perpendicular to the principal axis direction). The lateral anti-interference experimental results of the sensor were obtained. The experimental results show that:

[0085] The wavelength drift of the sensor in the main axis direction is 77 pm, and the wavelength drift in the non-main axis direction is 7 pm. Therefore, the lateral anti-interference degree of the present invention is about 9%, which can meet the engineering requirements.

[0086] The above description is only a preferred embodiment of the present invention. The scope of protection of the present invention is not limited to the above embodiments. Any equivalent modifications or changes made by those skilled in the art based on the content disclosed in the present invention should be included within the scope of protection set forth in the claims.

Claims

1. A high-sensitivity fiber-optic grating acceleration sensor, characterized by: The sensor comprises a base (1), a through-fiber block (2), an intermediate crossbeam (3) and a mass block (4), the top of the through-fiber block (2) is provided with a first fiber slot (21) which is transversely penetrated, the bottom of the through-fiber block (2) is connected with the top of the base (1), the bottom of the base (1) is fixedly connected with a to-be-measured object, the middle part of the base (1) is fixedly connected with the tail end (31) of the intermediate crossbeam (3), the free end (32) of the intermediate crossbeam (3) is fixedly connected with the middle part of the mass block (4), the top of the mass block (4) is provided with a second fiber slot (41) which is transversely penetrated, one end of a monitoring optical fiber (5) is arranged in the second fiber slot (41), the other end of the monitoring optical fiber (5) extends to the outside of the sensor after penetrating through the first fiber slot (21), and the bottom of the mass block (4) is higher than the bottom of the base (1). The parts of the monitoring optical fiber (5) which are located in the first fiber slot (21) and the second fiber slot (41) are connected with the first fiber slot (21) and the second fiber slot (41) correspondingly, the part of the monitoring optical fiber (5) which is located between the first fiber slot (21) and the second fiber slot (41) is a suspended optical fiber (51), the suspended optical fiber (51) is provided with a fiber grating (52), and the suspended optical fiber (51) and the intermediate crossbeam (3) which are arranged in parallel are clamped to form a fiber-beam spacing (53). The value of the fiber-beam spacing (53) is positively correlated with the sensitivity of the sensor and is irrelevant to the inherent frequency of the sensor.

2. The high-sensitivity fiber grating acceleration sensor according to claim 1, characterized in that: The middle part of the base (1) is connected with the tail end (31) of the intermediate crossbeam (3) perpendicularly, and the free end (32) of the intermediate crossbeam (3) is connected with the middle part of the mass block (4) perpendicularly.

3. The high-sensitivity fiber grating acceleration sensor according to claim 1 or 2, characterized in that: The width of the intermediate crossbeam (3) is ten times or more than ten times of the thickness of the intermediate crossbeam (3).

4. The high-sensitivity fiber grating acceleration sensor according to claim 1 or 2, characterized in that: The through-fiber block (2) is a cuboid structure, one end of the through-fiber block (2) is connected with the top of the base (1) in a flush manner, the other end of the through-fiber block (2) extends towards the mass block (4), the vertical projection of the other end of the through-fiber block (2) is located on the intermediate crossbeam (3), and the through-fiber block (2), the base (1) and the intermediate crossbeam (3) jointly form a block-beam clamping cavity (33) which is unidirectionally opened towards the mass block (4).

5. The high-sensitivity fiber grating acceleration sensor according to claim 1 or 2, characterized in that: The vertical projection of one end of the suspended optical fiber (51) is located on the intermediate crossbeam (3), and the vertical projection of the other end of the suspended optical fiber (51) is located on the mass block (4).

6. The high-sensitivity fiber grating acceleration sensor according to claim 5, characterized in that: The mass block (4) is a T-shaped structure, comprising a narrow top block (42) and a wide bottom block (43) which are connected in sequence, the side part of the wide bottom block (43) near the top thereof is connected with the free end (32) of the intermediate crossbeam (3), the top of the wide bottom block (43) is connected with the bottom of the narrow top block (42), and the top of the narrow top block (42) is provided with the second fiber slot (41) which is transversely penetrated.

7. The high-sensitivity fiber grating acceleration sensor according to claim 1 or 2, characterized in that: The sensitivity s of the sensor is wherein Pe is the photoelastic coefficient of the optical fiber, is the center wavelength of the optical fiber, h is the thickness of the intermediate beam (3), d is the value of the fiber-beam spacing (53), m is the mass of the mass block (4), L is the beam length of the intermediate beam (3), li, l2 are the horizontal distances between the two ends of the optical fiber grating (52) and the tail end (31), E is the elastic modulus of the intermediate beam (3), and b is the width of the intermediate beam (3).

8. The high-sensitivity fiber grating acceleration sensor according to claim 1 or 2, characterized in that: The sensor further comprises a shell (6) covering the base (1), the fiber passing block (2), the intermediate cross beam (3), the mass block (4) and the fiber grating (52), the bottom of the base (1) is fixedly connected with the inner side of a shell bottom plate (61) in the shell (6), the outer side of the shell bottom plate (61) is fixedly connected with the object to be measured, the bottom of the mass block (4) is suspended above the shell bottom plate (61), and the other end of the monitoring optical fiber (5) extends to the outside of the sensor after passing through the first fiber slot (21) and the shell (6) in sequence.

9. The high-sensitivity fiber-optic grating acceleration sensor of claim 8, wherein: The shell (6) is provided with a fiber passing hole (63) penetrating through the left side plate (62), and the other end of the monitoring optical fiber (5) extends to the outside of the sensor after passing through the first fiber slot (21) and the fiber passing hole (63) in sequence.

10. The high-sensitivity fiber grating acceleration sensor according to claim 1 or 2, characterized in that: The base (1), the fiber passing block (2), the intermediate cross beam (3) and the mass block (4) are integrated structures, and the manufacturing materials thereof are all 304 steel.

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