A fiber grating three-dimensional vector acceleration sensor

Abstract

The present application discloses a fiber Bragg grating three-dimensional vector acceleration sensor, which uses an inertial mass block through an integrated core structure. Compared with other three-dimensional sensors with multiple inertial mass blocks, one inertial mass block can avoid the problem of inconsistent mass centers of multiple mass blocks, making the acquisition of three-dimensional signals more accurate. Moreover, the resonance frequency and sensitivity in three directions are roughly the same, avoiding the problem of inconsistent sensitivity in three directions of traditional three-dimensional sensors, and the problem of excessive sensitivity in one direction easily causing damage to the sensor during use, enhancing the stability of the sensor and improving the accuracy of the measurement results.

Description

Technical Field

[0001] This application relates to the technical field of fiber optic sensors, and particularly to a fiber Bragg grating three-dimensional vector acceleration sensor. Background Art

[0002] As a passive device, a fiber Bragg grating (FGB) is a diffraction grating formed by axially modulating the refractive index of the fiber core through a certain technical method. Its essence is to write a series of phase gratings with periodic and permanent refractive index changes on the fiber core, forming a narrowband reflective optical wavelength selector that can reflect light near a specific wavelength. The wavelength of the reflected or transmitted wave of the fiber Bragg grating is related to the refractive index modulation period of the grating and the refractive index of the fiber core. When the external temperature or strain changes, it will affect the refractive index modulation period and the refractive index of the fiber core of the fiber Bragg grating, thereby causing a change in the reflected or transmitted wavelength of the fiber Bragg grating. The change in the external physical quantity is obtained by detecting the change in the center wavelength of the grating reflection.

[0003] Compared with traditional intensity modulation and phase modulation fiber optic sensors, fiber Bragg grating acceleration sensors not only have the advantages of high temperature resistance, corrosion resistance, and electromagnetic interference resistance, but also have the unique advantages of wavelength modulation type, which is conducive to wavelength division multiplexing and easy to implement a sensing network. Currently, most fiber Bragg grating acceleration sensors are one-dimensional. In practical applications, the acquisition of three-dimensional signals is more important. Therefore, one-dimensional acceleration sensors cannot meet the existing requirements. There are split-type three-dimensional acceleration sensors and integrated three-dimensional acceleration sensors for three-dimensional fiber Bragg grating acceleration sensors. The split type combines multiple one-dimensional fiber Bragg grating acceleration sensors. Generally, due to its own limitations, the split-type sensor has high installation complexity and cost, and because the inertial bodies in each direction are not at the same monitoring point, the finally detected data cannot truly reflect the three-dimensional acceleration signal of the monitoring point. The integrated type uses a single mass block to measure the three-dimensional acceleration signal. Compared with the split type, the integrated structure has an inertial mass block, and the sensitivity and resonance frequency in each direction are in good consistency, with high measurement accuracy, and it is also beneficial to the miniaturization of three-dimensional acceleration sensors.

[0004] Existing integrated acceleration sensors usually set a mass block in each of the three directions of the space coordinate system, and obtain the acceleration signals in the three directions received by the sensor through the drift amount of the center wavelength of the fiber Bragg grating. However, since different mass blocks are used in the three directions of the sensor, when a three-dimensional acceleration signal is transmitted to the sensor, the different mass blocks cause inconsistent reception of vibration signals in each direction, resulting in poor direction accuracy of the measured acceleration signal. Summary of the Invention

[0005] The embodiments of the present application provide a fiber Bragg grating three-dimensional vector acceleration sensor, which solves the problem of poor direction accuracy in measuring acceleration signals in the prior art.

[0006] To achieve the above object, the technical solution of the embodiments of the present invention is as follows:

[0007] In a first aspect, the embodiments of the present invention provide a fiber Bragg grating three-dimensional vector acceleration sensor, including: an integrated core structure, a housing, and fiber Bragg gratings; both the core structure and the housing are cube structures, and the core structure is supported and fixed at the center of the housing through a first fixing structure; the core structure includes an elastic body frame, a cube-shaped inertial mass block, and elastic structures respectively arranged on six surfaces of the elastic body frame; among them, the parameters of each elastic structure are the same, and each elastic structure has a through hole at the center, and a second fixing structure fixes the inertial mass block at the center of the elastic body frame through the through hole; on one side surface of three of the elastic structures facing the housing, one fiber Bragg grating is arranged respectively, and the central axes of any two of the three fiber Bragg gratings are skew lines and orthogonal to each other.

[0008] In some possible implementation manners, the elastic structure includes four rhombus structures, and the four rhombus structures form a symmetric structure, and the through hole is arranged at the intersection center of the four rhombus structures.

[0009] In some possible implementation manners, the fiber Bragg grating is fixed on the surface of the elastic structure through two-point encapsulation, and the fiber Bragg grating is along the diagonal of the rhombus structure, with one end fixed on the second fixing structure and the other end fixed on the elastic body frame.

[0010] In some possible implementation manners, the first fixing structure includes fixing buckles arranged at eight vertex positions of the elastic body frame, and the material of the fixing buckles is the same as that of the core structure.

[0011] In some possible implementation manners, the second fixing structure includes a single-pass hexagonal copper column arranged at the center of each elastic structure and a corresponding screw, and a threaded hole is arranged at the center of each surface of the inertial mass block; the bottom of the single-pass hexagonal copper column is fixed in the threaded hole at the center of the inertial mass block, and the threaded end of the screw passes through the through hole of the elastic structure and is threadedly connected to the top of the single-pass hexagonal copper column.

[0012] In some possible implementation manners, the materials of the elastic body frame, the elastic structure, and the inertial mass block are all brass.

[0013] In some possible implementation manners, the parameters of each fiber Bragg grating are the same, and the fiber Bragg grating is prestressed in advance so that the change amount of the central wavelength of the fiber Bragg grating meets a preset condition.

[0014] In some possible implementations, an optical fiber outlet hole is provided at the center of each of the three faces of the housing corresponding to the fiber Bragg grating, for leading out the fiber Bragg grating so that the fiber Bragg grating is connected to an external adjustment unit.

[0015] In some possible implementations, the position of the optical fiber outlet hole is cured by glue sealing.

[0016] One or more technical solutions provided in the embodiments of the present invention have at least the following technical effects or advantages:

[0017] In the embodiments of the present invention, through an integrated core structure and using one inertial mass block, compared with other three-dimensional sensors with multiple inertial mass blocks, one inertial mass block can avoid the problem of inconsistent centroid of multiple mass blocks, making the acquisition of three-dimensional signals more accurate. Moreover, the resonance frequencies and sensitivities in three directions are roughly the same, avoiding the problem of inconsistent sensitivities in three directions of traditional three-dimensional sensors, where excessive sensitivity in one direction during use is likely to cause damage to the sensor, enhancing the stability of the sensor and improving the accuracy of measurement results. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] To more clearly illustrate the embodiments of the present invention, the following will briefly introduce the drawings required for use in the embodiments of the present invention. Obviously, the drawings in the following description are some embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other drawings can also be obtained based on these drawings.

[0019] Figure 1 FIG. is a schematic three-dimensional structure diagram of an optical fiber Bragg grating three-dimensional vector acceleration sensor provided for the implementation of the present invention;

[0020] Figure 2 FIG. is a schematic Z-direction plane structure diagram of an optical fiber Bragg grating three-dimensional vector acceleration sensor in an embodiment of the present invention;

[0021] Figure 3 FIG. is a schematic structure diagram of an elastic structure of an optical fiber Bragg grating three-dimensional vector acceleration sensor in an embodiment of the present invention;

[0022] Figure 4a FIG. is a curve graph showing the change of resonance frequency and sensitivity at different thicknesses of the elastic structure;

[0023] Figure 4b FIG. is a curve graph showing the change of resonance frequency and sensitivity at different outer beam widths of the diamond structure of the elastic structure;

[0024] Figure 4c FIG. is a curve graph showing the change of resonance frequency and sensitivity at different inner beam widths of the diamond structure of the elastic structure;

[0025] Figure 4dThe graph of the resonant frequency and sensitivity variation of a rhombic structure with an elastic structure at different angles;

[0026] Figure 5 The schematic diagram of the amplitude-frequency characteristic curve of the acceleration sensor in the embodiment of the present invention;

[0027] Figure 6 The schematic diagram of the linearity curve of the acceleration sensor in the embodiment of the present invention;

[0028] Figure 7 The time-domain waveform diagram of the acceleration sensor in the X direction of the sensor at 200 Hz in the embodiment of the present invention;

[0029] Figure 8 The time-domain waveform diagram of the acceleration sensor in the Y direction of the sensor at 200 Hz in the embodiment of the present invention;

[0030] Figure 9 The time-domain waveform diagram of the acceleration sensor in the Z direction of the sensor at 200 Hz in the embodiment of the present invention.

[0031] In the figure, 11 is the core structure; 12 is the housing; 13 is the fiber grating; 14 is the first fixing structure; 111 is the elastic body frame; 112 is the inertial mass block; 113 is the elastic structure; 1131 is the through hole; 114 is the second fixing structure; 141 is the fixing buckle; 1132 is the rhombic structure; 1141 is the single-pass hexagonal copper column; 1142 is the screw; 121 is the fiber outlet hole. Specific Embodiments

[0032] Next, the technical solutions in the embodiments of the present application will be clearly and completely described in conjunction with the accompanying drawings in the embodiments of the present application. Obviously, the described embodiments are only a part of the embodiments of the present application, rather than all of the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the scope of protection of the present application.

[0033] In the relevant descriptions of this embodiment, terms such as "including, containing, having" are all open terms, generally preferably understood as including but not limited to; the term "at least one" is generally preferably understood as one or more, where "multiple" means two or more; the term "at least one (item) of the following" or its similar expression refers to any combination of these items, including any combination of single item (item) or plural items (items). For example, "at least one (item) of a, b or c", or, "at least one (item) of a, b and c" can all represent: a, b, c, a-b (i.e., a and b), a-c, b-c, or a-b-c, where a, b, c can be single or multiple respectively; the symbol "A / B" is used to describe the selection relationship of associated objects, generally representing an "or" relationship before and after.

[0034] In the following description of this embodiment, the terms used in the embodiments of this application are for the purpose of describing specific embodiments only and are not intended to limit this application. The singular forms "a" and "the" used in the embodiments of this application and the appended claims are also intended to include the plural forms unless the context clearly indicates otherwise.

[0035] Those skilled in the art should understand that in the following description of the embodiments of this application, the sequence numbers do not imply the order of execution, and some or all of the steps can be executed in parallel or sequentially. The execution order of each process should be determined by its function and internal logic, and should not constitute any limitation to the implementation process of the embodiments of this application.

[0036] Those skilled in the art should understand that the numerical ranges in the embodiments of this application should be understood to specifically disclose each intermediate value between the upper and lower limits of the range. The intermediate value within any stated value or range, as well as each smaller range between any other stated value or intermediate value within the range, is also included in the present invention. The upper and lower limits of these smaller ranges can be independently included or excluded from the range.

[0037] Unless otherwise specified, the technical / scientific terms used herein have the same meaning as commonly understood by those of ordinary skill in the art to which this application belongs. Although this application only describes preferred methods and materials, any methods and materials similar or equivalent to those described herein can also be used in the implementation or testing of this application. All documents mentioned in this specification are incorporated by reference to disclose and describe the methods and / or materials related to the documents. In case of conflict with any incorporated document, the content of this specification shall prevail.

[0038] In order to illustrate the technical solution of the present invention, specific embodiments will be used for illustration below.

[0039] As a passive device, a fiber Bragg grating is a diffraction grating formed by axially modulating the refractive index of the fiber core through a certain technical method. Its essence is to write a series of phase gratings with periodic and permanent refractive index changes on the fiber core to form a narrow-band reflective optical wavelength selector, which can reflect light near a specific wavelength. The wavelength of the reflected or transmitted wave of the fiber Bragg grating is related to the refractive index modulation period of the grating and the refractive index of the fiber core. When the external temperature or strain changes, it will affect the refractive index modulation period and the refractive index of the fiber core of the fiber Bragg grating, thereby causing a change in the reflected or transmitted wavelength of the fiber Bragg grating. By detecting the change in the center wavelength of the grating reflection, the change in the external physical quantity can be obtained.

[0040] Compared with traditional intensity - modulated and phase - modulated fiber optic sensors, fiber Bragg grating acceleration sensors not only have the advantages of high temperature resistance, corrosion resistance, and electromagnetic interference resistance, but also have unique advantages of wavelength modulation type, which is conducive to wavelength - division multiplexing and easy to implement a sensing network. Currently, most fiber Bragg grating acceleration sensors are one - dimensional. In practical applications, the acquisition of three - dimensional signals is more important. Therefore, one - dimensional acceleration sensors cannot meet the existing requirements. There are split - type three - dimensional acceleration sensors and integrated three - dimensional acceleration sensors for three - dimensional fiber Bragg grating acceleration sensors. The split - type combines multiple one - dimensional fiber Bragg grating acceleration sensors. Generally, due to its own limitations, the split - type sensor has high installation complexity and cost. Moreover, since the inertial bodies in each direction are not at the same monitoring point, the finally detected data cannot truly reflect the three - dimensional acceleration signal of the monitoring point. The integrated type uses a single mass block to measure three - dimensional acceleration signals. Compared with the split - type, the integrated structure has an inertial mass block, with good consistency of sensitivity and resonance frequency in each direction, high measurement accuracy, and is conducive to the miniaturization of three - dimensional acceleration sensors.

[0041] Existing integrated acceleration sensors usually set a mass block in each of the three directions of the space coordinate system, and obtain the acceleration signals in the three directions received by the sensor through the central wavelength drift of the fiber Bragg grating. However, since different mass blocks are used in the three directions of the sensor, when a three - dimensional acceleration signal is transmitted to the sensor, the different mass blocks cause inconsistent reception of vibration signals in each direction, resulting in poor direction accuracy of the measured acceleration signal.

[0042] Based on this, the embodiment of the present invention provides a fiber Bragg grating three - dimensional vector acceleration sensor to solve the problem of poor measurement result accuracy in the prior art.

[0043] See Figure 1 and Figure 2 as shown, Figure 1 is a three - dimensional structure schematic diagram of a fiber Bragg grating three - dimensional vector acceleration sensor provided by the embodiment of the present invention, Figure 2 is a schematic diagram of the Z - direction plane structure of a fiber Bragg grating three - dimensional vector acceleration sensor in the embodiment of the present invention. The above - mentioned fiber Bragg grating three - dimensional vector acceleration sensor may include:

[0044] An integrated core structure 11, a housing 12, and a fiber Bragg grating 13; both the core structure 11 and the housing 12 are cube structures, and the core structure 11 is supported and fixed at the center of the housing 12 through a first fixing structure 14;

[0045] The core structure 11 includes an elastic body frame 111, a cube - shaped inertial mass block 112, and elastic structures 113 respectively arranged on six faces of the elastic body frame 111, Figures 1 to 2In the figure, a1, a2, b1, b2, c1, and c2 respectively represent six elastic structures 113 disposed on six surfaces of the elastomeric frame 111. Among them, the parameters of each elastic structure 113 are the same. Each elastic structure 113 has a through hole 1131 at its center. The second fixing structure 114 fixes the inertial mass block 112 at the center of the elastomeric frame 111 through the through hole 1131;

[0046] One fiber Bragg grating 13 is disposed on the surface of each of the three elastic structures 113 facing the housing 12 in the elastic structure 113, Figure 1 In the figure, the fiber Bragg gratings 13 are respectively denoted as 13a, 13b, and 13c. The parameters of the fiber Bragg grating 13a, the fiber Bragg grating 13b, and the fiber Bragg grating 13c are the same; the central axes of any two of the three fiber Bragg gratings 13 are skew lines and perpendicular to each other.

[0047] It should be noted that the above core structure 11 is the core design or structure inside the acceleration sensor in the embodiment of the present invention for directly sensing and measuring acceleration changes. The core structure 11 is a structural module capable of responding to acceleration changes. When the sensor is subjected to acceleration, this core structure 11 will change, thereby generating a wavelength signal related to the acceleration.

[0048] It can be understood that in a complex vibration environment, if the connection between the core structure 11 and the housing 12 is not firm enough, then the external vibration may be transmitted to the core structure 11 through the housing 12, thereby interfering with the acceleration measurement. By supporting and fixing with the first fixing structure 14, this kind of vibration interference can be effectively isolated or reduced. At the same time, through precise support and fixing, it can be ensured that the core structure 11 only undergoes the expected deformation when subjected to acceleration, thereby improving the measurement accuracy.

[0049] In some embodiments, the first fixing structure 14 includes fixing buckles 141 disposed at eight vertex positions of the elastomeric frame 111, as Figure 1 shown, the fixing buckles 141 at eight vertex positions of the cubic elastomeric frame 111 are respectively denoted as 1411, 1412,..., 1418.

[0050] In some embodiments, the material of the fixing buckle 141 is the same as that of the core structure 11. Among them, the fixing buckle 141 and the core structure 11 can be fixed by welding, gluing, etc.

[0051] It can be understood that since different materials have different coefficients of thermal expansion, they will undergo different degrees of deformation when the temperature changes. If the materials of the fixing buckle 141 and the core structure 11 are different, the temperature change may cause relative displacement between the two, thereby affecting the performance of the sensor. Using the same material can ensure that they have similar deformations when the temperature changes, thus maintaining the structural stability. In addition, there may also be differences in the mechanical properties of different materials. Using the same material can ensure that the fixing buckle 141 and the core structure 11 have similar mechanical responses when subjected to external forces, thereby improving the measurement accuracy and reliability of the sensor. Finally, using the same material can also simplify the manufacturing process of the sensor and reduce the production cost.

[0052] In some embodiments, the materials of the above-mentioned elastomeric frame 111, elastic structure 113, and inertial mass block 112 can all be the same material. For example, brass, piezoelectric ceramics, semiconductors, etc. Which material to specifically select can depend on factors such as the actual application scenario, performance requirements, and cost of the acceleration sensor. In a preferred embodiment of the present invention, the materials of the above-mentioned structures can be brass.

[0053] In some embodiments, the elastic structure 113 includes four diamond structures 1132. Figure 3 It is a schematic structural diagram of the elastic structure 113 of a fiber Bragg grating three-dimensional vector acceleration sensor in an embodiment of the present invention. Refer to Figure 3 As shown, the four diamond structures 1132 form a symmetric structure, and the through hole 1131 is provided at the intersection center of the four diamond structures 1132.

[0054] In some embodiments, the fiber Bragg grating 13 can be fixed on the surface of the elastic structure 113 by two-point packaging. The fiber Bragg grating 13 is installed on the diagonal line of one of the four diamond structures 1132 of the elastic structure 113. And on the surface of the elastic structure 113 where the fiber Bragg grating 13 is installed, one end of the fiber Bragg grating 13 is fixed on the second fixing structure 114, and the other end passes through the diagonal line of the diamond structure 1132 and is fixed on the elastomeric frame 111. Among them, the fiber Bragg grating 13 can be fixed on the elastic structure 113 by gluing.

[0055] Exemplarily, also refer to Figure 1 As shown, in Figure 1Among them, the elastic structures 113 in the X direction are a1 and a2 respectively, the elastic structures 113 in the Y direction are b1 and b2 respectively, and the elastic structures 113 in the Z direction are c1 and c2 respectively. In the embodiment of the present invention, the fiber grating 13a is arranged on the elastic structure a1, and the central axis of the fiber grating 13a is along the Y-axis direction. The fiber grating 13b is arranged on the elastic structure b1, and the central axis of the fiber grating 13b is along the Z-axis direction. The fiber grating 13c is arranged on the elastic structure c1, and the central axis of the fiber grating 13c is along the X-axis direction.

[0056] It should be noted that the central axis of the fiber grating 13 refers to the center line of the optical fiber itself, that is, the geometric center of the optical fiber. In the optical fiber, the optical signal propagates along the core layer of the optical fiber, and the core layer is usually located at the center of the optical fiber.

[0057] In the embodiment of the present invention, the fiber grating 13 adopts a two-point packaging method, which can greatly simplify the packaging process and avoid the problem that the full adhesion packaging will cause the grating to generate a chirp effect. Since the elastomer frame 111 is a cube and the elastic structure 113 is symmetric, it is easier to find the orthogonal state of the gratings in the three directions of the split three-dimensional sensor. The three fiber gratings 13 are orthogonal to each other. Therefore, the signals received in the cross direction and the main vibration direction are in a sine angle relationship. When the signal is received in the main vibration direction of the sensor, it can effectively avoid sensitivity in other directions and improve the anti-lateral interference performance of the above acceleration sensor.

[0058] In some embodiments, the fiber grating 13 is prestressed in advance so that the change amount of the central wavelength of the fiber grating 13 meets a preset condition.

[0059] It can be understood that in the acceleration sensor, the wavelength response characteristic of the fiber grating is one of its key performance indicators. The central wavelength of the fiber grating will shift due to the change of physical quantities (such as temperature, strain, etc.) in its environment. In order to precisely control and utilize this wavelength shift, a prestress method can be adopted to adjust the performance of the fiber grating.

[0060] Among them, the preset condition can be an empirical value of a fiber grating 13, or it can also be specifically determined based on the requirements in the actual application process. For example, in the embodiment of the present invention, the preset condition can be that the change amount of the central wavelength of the fiber grating 13 is 4nm.

[0061] In some embodiments, the second fixing structure 114 includes a single-pass hexagonal copper column 1141 arranged at the center of each elastic structure 113 and a corresponding screw 1142. Also see Figure 1As shown, the bottom of the single-pass hexagonal copper column 1141 is fixed at the center of the inertial mass 112. Threaded holes matching the threads at the bottom of the single-pass hexagonal copper column 1141 are provided at the center of each face of the inertial mass 112. One end of the screw 1142 with threads can pass through the through hole 1131 of the elastic structure 113 and be threadedly connected to the top of the single-pass hexagonal copper column 1141.

[0062] In some embodiments, when one end of the fiber Bragg grating 13 is fixed to the second fixing structure 114, it can be fixed to the nut of the screw 1142 in the second fixing structure 114.

[0063] In some embodiments, fiber outlet holes 121 are provided at the centers of three faces of the housing 12 corresponding to the fiber Bragg grating 13. Also refer to Figure 1 As shown, the fiber outlet holes 121 are respectively provided on three faces corresponding to the elastic structure a1, the elastic structure b1, and the elastic structure c1. The fiber outlet holes 121 are used to lead out the fiber Bragg grating 13 so that the fiber Bragg grating 13 is connected to an external modulation unit.

[0064] Furthermore, the position of the fiber outlet hole 121 is solidified by glue sealing.

[0065] When the acceleration sensor provided by the embodiment of the present invention is in use, the acceleration sensor is installed on the object to be measured, and the signal transmission optical fiber is connected to the demodulation module of the fiber Bragg grating 13. When an external vibration signal acts on the object to be measured, under the action of inertia, the elastic diamond structures 1132 in the main vibration direction and the orthogonal direction of the inertial mass 112 will deform, causing the fiber Bragg grating 13 pasted in the middle of the elastic structure 113 and on the elastic body frame 111 to be stretched or compressed, thereby causing the spectral bandwidth to broaden and the reflected light intensity to change periodically. By collecting through a photoelectric detection device and processing the data, the change amplitude of the reflected light intensity is detected, so as to measure the amplitude and frequency of the object.

[0066] It should be noted that in the embodiment of the present invention, the elastic structure 113 is the main component in the core structure 11 that can generate a response based on the action of the inertial mass 112. By using different structural parameters of the elastic structure 113, such as the thickness of the elastic structure 113, the diagonal distance and width of the diamond structure 1132 of the elastic structure 113, etc., the performance of the sensor can be changed. In the embodiment of the present invention, the performance parameters are mainly reflected in the stability of the sensor, including the resonant frequency and sensitivity of the sensor, etc.

[0067] Exemplarily, FIG. 4 is a curve graph showing the change of the resonant frequency and sensitivity of the sensor under different structural parameters of the elastic structure 113 in the embodiment of the present invention. Among them, Figure 4a is the curve graph of the change of the resonant frequency and sensitivity under different thicknesses of the elastic structure 113, Figure 4bThe graph shows the changes in the resonance frequency and sensitivity of the rhombic structure 1132 of the elastic structure 113 under different outer beam widths. Figure 4c The graph shows the changes in the resonance frequency and sensitivity of the rhombic structure 1132 of the elastic structure 113 under different inner beam widths. Figure 4d The graph shows the changes in the resonance frequency and sensitivity of the rhombic structure 1132 of the elastic structure 113 under different angles.

[0068] Specifically, in the above embodiments, when other component parameters of the acceleration sensor remain unchanged, in the above Figure 4a the thickness of the elastic structure 113 in each direction, the diagonal distance of the rhombic structure 1132 in the elastic structure is 12.5 mm, its width is 1.25 mm, and its thickness becomes 0.2 mm, 0.3 mm and 0.4 mm. In Figure 4b the width of the rhombic structure 1132 in the elastic structure 113, the diagonal distance of the rhombic structure 1132 is 12.5 mm, the thickness is 0.1 mm, and its width starts from 1 mm and increases in steps of 0.05 mm to 1.4 mm in turn. In Figure 4c the connection angle of the rhombic structure 1132 in the elastic structure 113, the diagonal distance of the rhombic structure 1132 is 12.5 mm, the thickness is 0.1 mm, the width is 1.25 mm, and the connection angle between two sides of the rhombic structure 1132 starts from 90 degrees and increases in steps of 5 degrees to 180 degrees in turn. In Figure 4d the diagonal distance of the rhombic structure 1132 is 12.5 mm, the width is 1.25 mm, the thickness is 0.1 mm, and its inertial mass block 112 increases from 75 g in increments of 5 g respectively.

[0069] It can be understood that based on the above Figures 4a to 4b as shown, by changing the parameters of the elastic structure 113, the sensitivity and resonance frequency of the sensor will change synchronously. There is a mutual constraint between the sensitivity and the resonance frequency. When one increases, the other will decrease. Therefore, in order to ensure the optimal stability of the sensor, the parameters of the elastic structure 113 can be determined according to the requirements in actual applications to balance the relationship between the sensitivity and the resonance frequency, so as to achieve the most ideal performance.

[0070] It should be noted that the specific parameter values of the above Figures 4a to 4d corresponding elastic structure 113 are only an exemplary description. The specific parameters of the elastic structure 113 in the embodiments of the present invention can be determined based on the requirements in the actual application process.

[0071] The working principle of the acceleration sensor in the embodiments of the present invention is described below:

[0072] A FGB is encapsulated on the elastic structure of the acceleration sensor as described above. When the object under test vibrates, the inertial mass block vibrates. Under the action of inertia, deformation occurs on the elastic structure, which in turn causes the FGB adhered to the elastic structure to be stretched or compressed, and then causes the central wavelength of the FGB to drift. Therefore, by determining the corresponding relationship between the drift amount of the central wavelength of the FGB and the change of the acceleration signal, the acceleration signal can be measured by wavelength modulation.

[0073] Specifically, according to the coupled-mode theory, the FGB reflection spectrum can be expressed by the following formula (1):

[0074] (1)

[0075] Where, is the central wavelength of the FGB, is the effective refractive index of the optical fiber mode, is the period of the FGB.

[0076] When stress acts on the optical fiber, it will cause changes in the radius and length of the optical fiber, which in turn leads to changes in the grating period and effective refractive index. At this time, the change amount of the FBG central wavelength can be expressed by the following formula (2):

[0077] (2)

[0078] Where, is the radial strain of the FBG, is the change amount of the FBG diameter, is the photoelastic effect of the optical fiber, is the waveguide effect of the optical fiber, is the partial derivative symbol, is the diameter of the FBG, is the effective encapsulation length of the FBG.

[0079] Then the relative change amount of the wavelength of the FBG under the action of axial stress can be expressed by the following formula (3):

[0080] (3)

[0081] Where, Δλ B is the change amount of the FBG central wavelength, is the axial strain of the optical fiber, is the effective photoelastic coefficient. For fused silica optical fiber, the photoelastic coefficient

[0082] The acceleration sensor can be regarded as an inertial acceleration sensor. When an external acceleration excitation signal Acting on the inertial body, it will cause the inertial body to deviate from the equilibrium position. The external signal is a continuous sine signal , where is the amplitude of the vibration signal, is the angular frequency of the vibration signal. According to the inertia theory, the displacement motion equation of the inertial body can be expressed by the following formula (4):

[0083] (4)

[0084] where is the derivative symbol, is the displacement of the inertial body deviating from the equilibrium position, is the mass of the inertial body, is the damping of the system, eff is the equivalent stiffness of the system, is the time of the time-domain signal.

[0085] The amplitude of the system can be expressed by the following formula (5):

[0086] (5)

[0087] where is the damping ratio of the system, is the angular frequency of the system, is the frequency ratio, is the acceleration signal received by the sensor.

[0088] According to Newton's law, when the external acceleration signal changes, the acceleration signal can be expressed by the following formula (6):

[0089] (6)

[0090] where is the force acting on the system, is the change in FBG, is the equivalent stiffness of the sensor.

[0091] The sensitivity of the FBG acceleration sensor is defined as the ratio of the change in the central wavelength of FBG to and can be expressed by the following formula (7):

[0092] (7)

[0093] Combining the above formulas (3), (5), and (6), the sensitivity of the FBG acceleration detector can be expressed by the following formula (8):

[0094] (8)

[0095] When the frequency ratio approaches 0, the ideal acceleration sensitivity in the above formula (8) can be expressed by the following formula (9):

[0096] (9)

[0097] According to the vibration principle, the resonance frequency expression of the sensor can be obtained and can be expressed by the following formula (10):

[0098] (10)

[0099] Among them, the equivalent stiffness of the sensor , can be expressed by the following formula (11):

[0100] (11)

[0101] Among them, is the influence stiffness of the orthogonal direction on the main vibration direction, is the stiffness of the elastic structure in the main vibration direction, is the fiber optic stiffness in three directions.

[0102] In some embodiments, in order to verify the detection effect of the above acceleration sensor, the embodiments of the present invention conducted experiments on the above acceleration sensor, specifically including:[[]]

[0103] 1) Amplitude-frequency characteristic experiment:

[0104] The amplitude-frequency characteristic is one of the response characteristic parameters for measuring the FBG acceleration detector, which can reflect the resonance frequency, flat region, working frequency band, and flat region sensitivity of the detector. In the amplitude-frequency response experiment of the sensor, in the embodiments of the present invention, taking the example of applying an acceleration of 0.5g to the sensor at different frequencies, and then obtaining the wavelength drift amount of the same acceleration signal at different frequencies, the amplitude-frequency characteristic curve of the sensor is obtained as Figure 5 shown. Figure 5 is a schematic diagram of the amplitude-frequency characteristic curve of the acceleration sensor of the present invention example, see Figure 5 shown. The flat regions in the three directions are roughly the same. It can be determined that the flat regions in the X, Y, and Z directions of the sensor are 20~190Hz, 20~205Hz, and 30~205Hz respectively, and the sensor can work normally within this frequency range.

[0105] 2) Linear sensitivity curve:

[0106] The sensitivity is the ratio between the output wavelength of the detector and the acceleration amplitude. In the linear sensitivity experiment of the sensor, in the embodiments of the present invention, taking the wavelength change at 100 Hz in three directions as an example, where the acceleration peak value of the sensor is used as the output signal, the amplitude of the acceleration sensor increases from 0.2 G to 3.0 G in steps of 0.2 G, and the linear relationship between the wavelength peak change of the sensor and the acceleration signal can be as Figure 6 shown. Figure 6 It is a schematic diagram of the linearity curve of the acceleration sensor in the embodiments of the present invention, Figure 6 indicating that the sensor has a good linear relationship. The sensitivity in the X direction at a frequency of 150 Hz is 168 pm / G (R 2 = 0.998), the sensitivity in the Y direction is 158 pm / G (R 2 = 0.999), and the sensitivity in the Z direction is 133 pm / G (R 2 = 0.999).

[0107] 3) Time-domain waveform curve:

[0108] See Figure 7 、 Figure 8 and Figure 9 shown, where Figure 7 is the time-domain waveform diagram of the acceleration sensor in the X direction of the embodiments of the present invention at 200 Hz, Figure 8 is the time-domain waveform diagram of the acceleration sensor in the Y direction of the embodiments of the present invention at 200 Hz, Figure 9 is the time-domain waveform diagram of the acceleration sensor in the Z direction of the embodiments of the present invention at 200 Hz. The waveforms in the X, Y, and Z directions of the sensor at 200 Hz are intact sine curves, which are consistent with the waveform of the input signal of the vibration table, indicating that the linear relationship between the input and output signals of the sensor is good.

[0109] In the embodiments of the present invention, first, the elastic structures on the six surfaces of the elastic body frame adopt four diamond structures as the sensitive elements for vibration signals. This sensitive element can well concentrate the strain area on the elastic structure. Compared with the straight beams, hinges, multi-beams, etc. of other three-dimensional sensors, it can improve the sensitivity of the sensor and reduce the boundary effect, enabling the vibration signal to be well received.

[0110] Secondly, the embodiments of the present invention adopt an inertial mass block. Compared with other three-dimensional sensors with multiple inertial mass blocks, adopting one inertial mass block can avoid the problem of inconsistent centroid of multiple mass blocks, making the acquisition of three-dimensional signals more accurate. Moreover, the resonant frequencies and sensitivities in the three directions are roughly the same, avoiding the problem of inconsistent sensitivities in the three directions of traditional three-dimensional sensors. In use, if the sensitivity in one direction is too large, it is easy to cause damage to the sensor, enhancing the stability of the sensor.

[0111] In addition, an inertial mass block is adopted to integrate the elastic bodies in three directions, greatly reducing the volume of the sensor. Since the resonance frequencies and sensitivities in three directions are nearly the same, the directionality of the sensor is not strict during actual installation and use, and any surface can be used as the main vibration direction, so it will bring great convenience in actual use.

[0112] Finally, in the embodiment of the present invention, the grating adopts a two-point packaging method, which greatly simplifies the packaging process of the optical fiber and avoids the problem that the full-adhesive packaging will cause the grating to generate a chirp effect. Since the sensor frame is a cube and the elastic body is symmetric, it is easier to find the orthogonal state of the gratings in three directions compared with the split three-dimensional sensor, and the three optical fibers are orthogonal to each other. Therefore, the signals received in the cross direction and the main vibration direction are in a relationship of a sine angle. When the signal is received in the main vibration direction of the sensor, it can effectively avoid sensitivity in other directions. Therefore, the sensor has strong anti-lateral interference performance.

[0113] The various embodiments in this specification are described in a progressive manner. For the same or similar parts between the various embodiments, reference can be made to each other. The key points of each embodiment are the differences from other embodiments.

[0114] The above embodiments are only used to illustrate the technical solutions of the present application, rather than limiting the present application; although the present application has been described in detail with reference to the foregoing embodiments, those of ordinary skill in the art should understand that they can still modify the technical solutions recorded in the foregoing embodiments, or perform equivalent replacements on some or all of the technical features; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the scope of the technical solutions of the present application.

Claims

1. A fiber Bragg grating three-dimensional vector acceleration sensor, characterized in that: include: An integrated core structure, shell and optical fiber Bragg grating; the core structure and the shell are both cube structures, and the core structure is supported and fixed at the center of the shell by a first fixing structure; The core structure includes an elastic body frame, an inertial mass block of a cube structure, and elastic structures respectively arranged on six faces of the elastic body frame; wherein the parameters of each of the elastic structures are the same, each of the elastic structures has a through hole at the center, and the second fixing structure fixes the inertial mass block at the center of the elastic body frame through the through hole; The elastic structure includes four rhombus structures, the four rhombus structures form a symmetrical structure, and the through hole is arranged at the center of the intersection of the four rhombus structures; A fiber Bragg grating is respectively arranged on a side surface of three of the elastic structures facing the shell, and the central axes of any two of the three fiber Bragg gratings are skew lines and orthogonal to each other; wherein the fiber Bragg grating is fixed to the surface of the elastic structure through a two-point package, and one end of the fiber Bragg grating is fixed to the second fixed structure along the diagonal of the diamond structure, and the other end is fixed to the elastic body frame; the acceleration sensor measures the acceleration signal by wavelength modulation by determining the corresponding relationship between the drift amount of the central wavelength of the fiber Bragg grating and the change of the acceleration signal.

2. The acceleration sensor according to claim 1, characterized in that The first fixing structure includes fixing buckles arranged at eight vertices of the elastic frame, and the material of the fixing buckles is the same as that of the core structure.

3. The acceleration sensor according to claim 1, characterized in that: The second fixing structure includes a single-pass hexagonal copper column and a corresponding screw arranged in the center of each elastic structure, and a threaded hole is arranged in the center of each face of the inertial mass block; the bottom of the single-pass hexagonal copper column is fixed in the threaded hole in the center of the inertial mass block, and the screw has a threaded end that passes through the through hole of the elastic structure and is threadedly connected to the top of the single-pass hexagonal copper column.

4. The acceleration sensor according to claim 1, characterized in that: The elastic frame, the elastic structure and the inertial mass block are all made of brass.

5. The acceleration sensor according to claim 1, characterized in that: The parameters of each fiber Bragg grating are the same, and the fiber Bragg grating is pre-stressed in advance so that the variation of the central wavelength of the fiber Bragg grating meets the preset conditions.

6. The acceleration sensor according to claim 1, characterized in that: The center of each of the three surfaces of the shell corresponding to the fiber Bragg grating is provided with a fiber outlet hole for leading out the fiber Bragg grating so as to connect the fiber Bragg grating with an external mediation unit.

7. The acceleration sensor according to claim 6, characterized in that: The fiber outlet hole position is solidified by glue sealing.

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