CN118624936A

CN118624936A - Fiber bragg grating three-dimensional vector acceleration sensor

Info

Publication number: CN118624936A
Application number: CN202410677694.6A
Authority: CN
Inventors: 刘钦朋; 闫诚; 刘波; 杨迪; 邢美华; 禹大宽; 高宏
Original assignee: Xian Shiyou University
Current assignee: Xian Shiyou University
Priority date: 2024-05-29
Filing date: 2024-05-29
Publication date: 2024-09-10

Abstract

The application discloses a fiber bragg grating three-dimensional vector acceleration sensor, which adopts an inertial mass block through an integrated core structure, and compared with other three-dimensional sensors with multiple inertial mass blocks, the three-dimensional vector acceleration sensor has the advantages that one inertial mass block can avoid the problem of inconsistent mass centers of the multiple mass blocks, so that the acquisition of three-dimensional signals is more accurate. And the resonance frequency and the sensitivity of the three directions are approximately the same, so that the problem that the sensor is damaged easily due to overlarge sensitivity of one direction in use is avoided, the stability of the sensor is enhanced, and the accuracy of a measuring result is improved.

Description

Fiber bragg grating three-dimensional vector acceleration sensor

Technical Field

The application relates to the technical field of optical fiber sensors, in particular to an optical fiber grating three-dimensional vector acceleration sensor.

Background

The fiber grating (Fiber Bragg Grating, FGB) is a passive device, and is a diffraction grating formed by axially modulating the refractive index of the fiber core by a certain technical method. The essence is to write a series of phase gratings with periodicity and permanently changed refractive index on the fiber core to form a narrow-band reflective optical wavelength selector which can reflect light with specific wavelength accessories. The wavelength of the reflected or transmitted wave of the fiber grating is related to the refractive index modulation period of the grating and the refractive index of the fiber core, when the change of the external temperature or strain affects the refractive index modulation period of the fiber grating and the refractive index of the fiber core, the change of the reflected or transmitted wavelength of the fiber grating is caused, and the change of the external physical quantity is obtained by detecting the change of the reflected central wavelength of the grating.

Compared with the traditional intensity-modulated and phase-modulated optical fiber sensor, the optical fiber grating acceleration sensor has the advantages of high temperature resistance, corrosion resistance and electromagnetic interference resistance, has the unique advantage of wavelength modulation, is beneficial to wavelength division multiplexing, and is easy to realize a sensing network. The existing fiber grating acceleration sensor is one-dimensional, in practical application, three-dimensional signal acquisition is more important, so that the one-dimensional acceleration sensor cannot meet the existing requirements, the three-dimensional fiber grating acceleration sensor is provided with a split three-dimensional acceleration sensor and an integrated three-dimensional acceleration sensor, the split three-dimensional fiber grating acceleration sensor is formed by combining a plurality of one-dimensional fiber grating acceleration sensors, the split three-dimensional fiber grating acceleration sensor is high in installation complexity and high in cost due to self limitation, and the three-dimensional acceleration signals of monitoring points cannot be truly reflected by finally detected data due to the fact that inertia bodies in all directions are not located on the same monitoring point; the integrated type is that a mass block is adopted to realize measurement of three-dimensional acceleration signals, compared with a split type, the integrated type structure is provided with an inertial mass block, the sensitivity and resonance frequency of each direction are good in consistency, the measurement accuracy is high, and the miniaturization of the three-dimensional acceleration sensor is facilitated.

The existing integrated acceleration sensor is generally provided with a mass block in three directions of a space coordinate system, and acceleration signals in the three directions of the sensor are obtained through the central wavelength drift amount of the fiber bragg grating. However, since the sensor adopts different mass blocks in three directions, when a three-dimensional acceleration signal is transmitted to the sensor, the vibration signals in different directions are received unevenly due to the different mass blocks, and the direction accuracy of the measured acceleration signal is poor.

Disclosure of Invention

The embodiment of the application solves the problem of poor direction accuracy of an acceleration signal measured by the prior art by providing the fiber bragg grating three-dimensional vector acceleration sensor.

In order to achieve the above object, the technical solution of the embodiment of the present invention is:

In a first aspect, an embodiment of the present invention provides a fiber bragg grating three-dimensional vector acceleration sensor, including: an integrated core structure, a shell and a fiber grating; the core structure and the shell are both of cube structures, and the core structure is supported and fixed at the center of the shell through a first fixing structure; the core structure comprises an elastomer frame, an inertial mass block of a cube structure and elastic structures respectively arranged on six surfaces of the elastomer frame; the second fixing structure fixes the inertial mass block at the center of the elastic body frame through the through holes; one side surface of each of the three elastic structures facing the shell is provided with one fiber bragg grating, and the central axes of any two fiber bragg gratings in the three fiber bragg gratings are different-plane straight lines and mutually orthogonal.

In some possible implementations, the elastic structure includes four diamond structures, the four diamond structures forming a symmetrical structure, the through hole being disposed at a center of intersection of the four diamond structures.

In some possible implementations, the fiber grating is fixed to the surface of the elastic structure through a two-point package, and the fiber grating is fixed to the second fixing structure along a diagonal line of the diamond structure, and is fixed to the elastic body frame at one end and the other end.

In some possible implementations, the first fixing structure includes fixing buckles disposed at eight vertex positions of the elastomer frame, and a material of the fixing buckles is the same as that of the core structure.

In some possible implementations, the second fixing structure includes a single-pass hexagonal copper column disposed at the center of each elastic structure and a corresponding screw, and each face center of the inertial mass block is provided with a threaded hole; the bottom of the single-pass hexagonal copper column is fixed in a threaded hole in the center of the inertial mass block, and one end with threads of the screw penetrates through a through hole of the elastic structure to be in threaded connection with the top of the single-pass hexagonal copper column.

In some possible implementations, the elastomeric frame, the elastomeric structure, and the inertial mass are all brass.

In some possible implementations, the parameters of each fiber grating are the same, and the fiber grating is pre-stressed to enable the variation of the center wavelength of the fiber grating to meet the preset condition.

In some possible implementations, the center of the three surfaces of the housing, where the fiber gratings are correspondingly disposed, is provided with a fiber outlet hole, for leading out the fiber gratings, so that the fiber gratings are connected with an external adjusting unit.

In some possible implementations, the fiber-exit locations are cured by glue sealing.

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

In the embodiment of the invention, through an integrated core structure, one inertial mass block is adopted, and compared with other three-dimensional sensors with multiple inertial mass blocks, one inertial mass block can avoid the problem of inconsistent mass centers of the multiple mass blocks, so that the acquisition of three-dimensional signals is more accurate. And the resonance frequency and the sensitivity of the three directions are approximately the same, so that the problem that the sensor is damaged easily due to overlarge sensitivity of one direction in use is avoided, the stability of the sensor is enhanced, and the accuracy of a measuring result is improved.

Drawings

In order to more clearly illustrate the embodiments of the present invention, the drawings that are required to be used in the embodiments of the present invention will be briefly described below, and it will be apparent that the drawings in the following description are some embodiments of the present invention, and other drawings may be obtained according to these drawings without inventive effort to those of ordinary skill in the art.

FIG. 1 is a schematic diagram of a three-dimensional structure of a fiber grating three-dimensional vector acceleration sensor according to the embodiment of the present invention;

FIG. 2 is a schematic view of a Z-direction plane structure of a fiber bragg grating three-dimensional vector acceleration sensor according to an embodiment of the present invention;

FIG. 3 is a schematic structural diagram of an elastic structure of a fiber grating three-dimensional vector acceleration sensor according to an embodiment of the present invention;

FIG. 4a is a graph showing the variation of resonant frequency and sensitivity of an elastic structure at different thicknesses;

FIG. 4b is a graph of the resonant frequency and sensitivity variation for different outer beam widths for a diamond-shaped structure of the spring structure;

FIG. 4c is a graph of the resonant frequency and sensitivity variation for different inner beam widths for a diamond-shaped structure of the spring structure;

FIG. 4d is a graph showing the variation of resonant frequency and sensitivity of a diamond-shaped structure of an elastic structure at different angles;

FIG. 5 is a schematic diagram showing an amplitude-frequency characteristic of an acceleration sensor according to an embodiment of the present invention;

FIG. 6 is a schematic diagram of a linear curve of an acceleration sensor according to an embodiment of the present invention;

FIG. 7 is a time domain waveform diagram of an acceleration sensor of an example of the present invention in the X direction of the sensor at 200 Hz;

FIG. 8 is a time domain waveform diagram of an acceleration sensor of an example of the present invention in the Y direction of the sensor at 200 Hz;

fig. 9 is a time domain waveform diagram of the acceleration sensor of the embodiment of the present invention in the Z direction of the sensor at 200 Hz.

11, Core structure; 12. a housing; 13. an optical fiber grating; 14. a first fixed structure; 111. an elastomeric frame; 112. an inertial mass; 113. an elastic structure; 1131. a through hole; 114. a second fixing structure; 141. a fixing buckle; 1132. a diamond structure; 1141. single pass hexagonal copper column; 1142. a screw; 121. and a fiber outlet hole.

Detailed Description

The technical solutions in the embodiments of the present application will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present application. It will be apparent that the described embodiments are some, but not all, embodiments of the application. All other embodiments, which can be made by those skilled in the art based on the embodiments of the application without making any inventive effort, are intended to be within the scope of the application.

In the description of the present embodiments, the terms "include, comprise, have," etc. are open-ended terms that generally and preferably include, but are not limited to; the term "at least one" is generally understood to mean one or more, where "plurality" means two or more; the term "at least one of (a)," or similar expressions thereof, refers to any combination of these items, including any combination of single item(s) or plural items(s), for example, "at least one of (a)," or "at least one of (a)," b and c ", each of which may represent: a, b, c, a-b (i.e., a and b), a-c, b-c, or a-b-c, wherein a, b, c may be single or multiple, respectively; the symbol "a/B" is used to describe a selected relationship of associated objects, and generally indicates a relationship of "or" before and after.

In the following description of the present embodiment, the terminology used in the embodiments of the application is for the purpose of describing particular embodiments only and is not intended to be limiting of the application. As used in this application and the appended claims, the singular forms "a," "an," and "the" are intended to include the plural forms as well, unless the context clearly indicates otherwise.

It should be understood by those skilled in the art that, in the following description of the present embodiment, the sequence number does not mean that the execution sequence is sequential, and some or all of the steps may be executed in parallel or sequentially, and the execution sequence of each process should be determined by its functions and inherent logic, and should not constitute any limitation on the implementation process of the embodiment of the present application.

It will be appreciated by those skilled in the art that the numerical ranges in the embodiments of the present application are to be understood as also specifically disclosing each intermediate value between the upper and lower limits of the range. Every smaller range between any stated value or stated range, and any other stated value or intermediate value within the range, is also encompassed by the application. The upper and lower limits of these smaller ranges may independently be included or excluded in the range.

Unless otherwise defined, technical/scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs. Although only preferred methods and materials are described herein, any methods and materials similar or equivalent to those described herein can be used in the practice or testing of the present application. All documents referred to in this specification are incorporated by reference herein to disclose and describe the methods and/or materials in connection with which the documents are to be. In case of conflict with any incorporated document, the present specification will control.

In order to illustrate the technical scheme of the invention, the following description is made by specific examples.

The fiber grating is a passive device, and is a diffraction grating formed by axially modulating the refractive index of a fiber core by a certain technical method. The essence is to write a series of phase gratings with periodicity and permanently changed refractive index on the fiber core to form a narrow-band reflective optical wavelength selector which can reflect light with specific wavelength accessories. The wavelength of the reflected or transmitted wave of the fiber grating is related to the refractive index modulation period of the grating and the refractive index of the fiber core, when the change of the external temperature or strain affects the refractive index modulation period of the fiber grating and the refractive index of the fiber core, the change of the reflected or transmitted wavelength of the fiber grating is caused, and the change of the external physical quantity is obtained by detecting the change of the reflected central wavelength of the grating.

Based on the above, the embodiment of the invention provides a fiber bragg grating three-dimensional vector acceleration sensor which is used for solving the problem of poor accuracy of measurement results in the prior art.

Referring to fig. 1 and fig. 2, fig. 1 is a schematic perspective view of a three-dimensional vector acceleration sensor with fiber bragg grating according to an embodiment of the present invention, and fig. 2 is a schematic view of a Z-direction plane structure of a three-dimensional vector acceleration sensor with fiber bragg grating according to an embodiment of the present invention. The fiber bragg grating three-dimensional vector acceleration sensor may include:

an integrated core structure 11, a shell 12 and a fiber grating 13; the core structure 11 and the shell 12 are both square structures, and the core structure 11 is supported and fixed in the center of the shell 12 through the first fixing structure 14;

The core structure 11 includes an elastomer frame 111, a inertial mass 112 of a square structure, and elastic structures 113 disposed on six sides of the elastomer frame 111, and in fig. 1 to 2, six elastic structures 113 disposed on six sides of the elastomer frame 111 are denoted by a1, a2, b1, b2, c1, and c2, respectively. Wherein, parameters of the elastic structures 113 are the same, a through hole 1131 is formed in the center of each elastic structure 113, and the second fixing structure 114 fixes the inertial mass 112 in the center of the elastic body frame 111 through the through hole 1131;

One optical fiber grating 13 is respectively arranged on one side surface of the three elastic structures 113 facing the shell 12, the optical fiber gratings 13 are respectively indicated as 13a, 13b and 13c in fig. 1, and parameters of the optical fiber gratings 13a, 13b and 13c are the same; the central axes of any two fiber gratings 13 in the three fiber gratings 13 are different-plane straight lines and are mutually orthogonal.

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

It will be appreciated that in a complex vibration environment, if the connection between the core structure 11 and the housing 12 is not sufficiently strong, external vibrations may be transmitted to the core structure 11 through the housing 12, thereby interfering with the measurement of acceleration. Such vibration disturbances may be effectively isolated or reduced by the supporting fixation of the first fixation structure 14. Meanwhile, through accurate support and fixation, the core structure 11 can be ensured to only deform expected when being subjected to acceleration, so that the measurement accuracy is improved.

In some embodiments, the first fixing structure 14 includes fixing snaps 141 disposed at eight vertex positions of the elastomer frame 111, and as shown in fig. 1, the fixing snaps 141 at eight vertex positions of the elastomer frame 111 of the square structure are denoted by 1411, 1412, …, 1418, respectively.

In some embodiments, the material of the fixing buckle 141 is the same as that of the core structure 11. The fixing buckle 141 and the core structure 11 may be fixed by welding, gluing, or the like.

It will be appreciated that different materials have different coefficients of thermal expansion and will deform to different extents as the temperature changes. If the materials of the fixing clasp 141 and the core structure 11 are different, a temperature change may cause a relative displacement between the two, thereby affecting the performance of the sensor. The use of the same materials ensures that they have similar deformations when temperature changes, thus maintaining structural stability. In addition, there may be differences in the mechanical properties of the different materials. The use of the same material ensures that the fixing clasp 141 and the core structure 11 have similar mechanical response when subjected to external forces, thereby improving the measurement accuracy and reliability of the sensor. Finally, the use of the same material can also simplify the manufacturing process of the sensor and reduce the production cost.

In some embodiments, the materials of the elastomer frame 111, the elastic structure 113, and the inertial mass 112 may all be the same. Such as brass, piezoelectric ceramics, semiconductors, etc. The specific choice of which material may 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 structures may be brass.

In some embodiments, the elastic structure 113 includes four diamond-shaped structures 1132. Fig. 3 is a schematic structural diagram of an elastic structure 113 of a fiber bragg grating three-dimensional vector acceleration sensor according to an embodiment of the present invention. Referring to fig. 3, four diamond structures 1132 form a symmetrical structure, and a through hole 1131 is disposed at the center of the intersection of the four diamond structures 1132.

In some embodiments, the fiber grating 13 may be fixed to the surface of the elastic structure 113 by a two-point type package, the fiber grating 13 is mounted on a diagonal line of one diamond-shaped structure 1132 among four diamond-shaped structures 1132 of the elastic structure 113, and on the surface of the elastic structure 113 on which the fiber grating 13 is mounted, the fiber grating 13 is fixed to the second fixing structure 114 at one end and to the elastic body frame 111 at the other end through the diagonal line of the diamond-shaped structure 1132. The fiber grating 13 may be fixed on the elastic structure 113 by gluing.

For example, referring also to fig. 1, in fig. 1, 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 invention, the fiber grating 13a is arranged on the elastic structure a1, 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, 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.

The central axis of the fiber grating 13 refers to the central axis of the fiber itself, that is, the geometric center of the fiber. In an optical fiber, an optical signal propagates along the core of the optical fiber, which is typically located in the center of the optical fiber.

In the embodiment of the invention, the fiber grating 13 is packaged in two points, so that the packaging process can be greatly simplified, and the problem that the whole-adhesion type packaging can cause the chirp effect of the grating is avoided. Because the elastomer frame 111 adopts the cube and the elastic structure 113 is symmetrical, compared with the grating in three directions of the split three-dimensional sensor, the orthogonal state is easier to find, and the three fiber gratings 13 are mutually orthogonal, so that signals received in the cross direction and the main vibration direction are in a relationship of a sine angle, when the signals are received in the main vibration direction of the sensor, the sensitivity in other directions can be effectively avoided, and the transverse interference resistance of the acceleration sensor can be improved.

In some embodiments, the fiber grating 13 is pre-stressed such that the amount of change in the center wavelength of the fiber grating 13 satisfies a preset condition.

It will be appreciated that in the acceleration sensor. The wavelength response characteristic of the fiber bragg grating is one of the key performance indexes. The center wavelength of the fiber grating may shift due to changes in physical quantities (e.g., temperature, strain, etc.) of the environment in which the fiber grating is located. In order to precisely control and utilize this wavelength shift, the performance of the fiber grating may be adjusted in a pre-stressed manner.

The preset condition may be an empirical value of the fiber bragg grating 13, or may be specifically determined based on the requirements in the practical application process. For example, in the embodiment of the present invention, the preset condition may be that the central wavelength variation of the fiber grating 13 is 4nm.

In some embodiments, the second fixation structure 114 includes a single pass hexagonal copper post 1141 and a corresponding screw 1142 disposed in the center of each spring structure 113. Referring also to fig. 1, the bottom of the single-pass hexagonal copper pillar 1141 is fixed at the center of the inertial mass 112, each surface center of the inertial mass 112 is provided with a threaded hole matching with the threads at the bottom of the single-pass hexagonal copper pillar 1141, and one threaded end of the screw 1142 can pass through the through hole 1131 of the elastic structure 113 to be in threaded connection with the top of the single-pass hexagonal copper pillar 1141.

In some embodiments, when one end of the fiber bragg grating 13 is fixed to the second fixing structure 114, the fiber bragg grating may be fixed to a nut of the screw 1142 in the second fixing structure 114.

In some embodiments, the center of the three surfaces of the housing 12, where the fiber bragg gratings 13 are correspondingly disposed, is provided with one fiber outlet 121. Referring also to fig. 1, the fiber holes 121 are respectively provided on three faces corresponding to the elastic structures a1, b1 and c 1. The fiber outlet 121 is used for leading out the fiber grating 13, and connecting the fiber grating 13 with an external adjusting unit.

Further, the position of the fiber outlet hole 121 is cured by glue sealing.

When the acceleration sensor provided by the embodiment of the invention is used, the acceleration sensor is arranged on a measured object, the signal transmission optical fiber is connected with the optical fiber grating 13 demodulation module, when an external vibration signal acts on the measured object, the inertial mass block 112 deforms under the action of inertia, the elastic diamond-shaped structure 1132 in the main vibration direction and the orthogonal direction, so that the optical fiber grating 13 stuck in the middle of the elastic structure 113 and on the elastic body frame 111 stretches or is compressed, further the spectral bandwidth is widened, the reflected light intensity is periodically changed, and the amplitude of the change of the reflected light intensity is detected through the acquisition and the data processing of the photoelectric detection equipment, so that the amplitude and the frequency of the object are measured.

It should be noted that, in the embodiment of the present invention, the elastic structure 113 is a main component of the core structure 11 capable of generating a response based on the interaction of the inertial mass 112, and the performance of the sensor may be changed by adopting different structural parameters of the elastic structure 113, such as the thickness of the elastic structure 113, the diagonal distance and the width of the diamond-shaped structure 1132 of the elastic structure 113, and so on. In the embodiment of the invention, the performance parameters are mainly reflected in the stability of the sensor, including the resonance frequency, sensitivity and the like of the sensor.

Fig. 4 is a graph illustrating the change in the resonant frequency and sensitivity of the sensor under the structural parameters of different elastic structures 113 according to an embodiment of the present invention. Fig. 4a is a graph of resonance frequency and sensitivity variation of the elastic structure 113 with different thicknesses, fig. 4b is a graph of resonance frequency and sensitivity variation of the diamond structure 1132 of the elastic structure 113 with different outer beam widths, fig. 4c is a graph of resonance frequency and sensitivity variation of the diamond structure 1132 of the elastic structure 113 with different inner beam widths, and fig. 4d is a graph of resonance frequency and sensitivity variation of the diamond structure 1132 of the elastic structure 113 with different angles.

Specifically, in the above embodiment, the parameters of other components of the acceleration sensor are unchanged, and in fig. 4a, the thickness of the elastic structure 113 in each direction, the diagonal distance of the diamond-shaped structure 1132 in the elastic structure is 12.5mm, the width thereof is 1.25mm, and the thickness thereof is 0.2mm, 0.3mm, and 0.4mm. In fig. 4b, the width of the diamond 1132 in the elastic structure 113, the diagonal distance of the diamond 1132, is 12.5mm, the thickness is 0.1mm, and the width starts from 1mm and increases to 1.4mm in steps of 0.05 mm. In fig. 4c, the connection angle of the diamond-shaped structure 1132 in the elastic structure 113, the diagonal distance of the diamond-shaped structure 1132 is 12.5mm, the thickness is 0.1mm, the width is 1.25mm, and the connection angle between two sides of the diamond-shaped structure 1132 increases from 90 degrees in steps of 5 degrees, and increases to 180 degrees in turn. In fig. 4d, the diamond 1132 has a diagonal distance of 12.5mm, a width of 1.25mm, and a thickness of 0.1mm, with the inertial mass 112 increasing from 75g in 5g increments, respectively.

It will be appreciated that by varying the parameters of the elastic structure 113, the sensitivity and resonant frequency of the sensor will be varied simultaneously, constrained by each other, and increased one by one, based on the above description of fig. 4a to 4 b. Therefore, to ensure the optimal stability of the sensor, the parameters of the elastic structure 113 may be determined according to the requirements in practical applications, so as to balance the relationship between the sensitivity and the resonant frequency, thereby achieving the optimal performance.

It should be noted that the specific parameter values of the elastic structure 113 corresponding to fig. 4a to 4d are only exemplary, and the parameters of the specific elastic structure 113 in the embodiment of the present invention may be determined based on the requirements in the practical application process.

The working principle of the acceleration sensor according to the embodiment of the invention is described below:

When the object to be measured vibrates, the inertial mass vibrates, and the elastic structure deforms under the action of inertia, so that the FGB adhered to the elastic structure is stretched or compressed, and the center wavelength of the FGB shifts, and therefore the acceleration signal can be measured by utilizing wavelength modulation by determining the corresponding relation between the shift amount of the center wavelength of the FGB and the change of the acceleration signal.

Specifically, according to the coupled mode theory, FGB reflectance spectrum can be represented by the following formula (1):

（1）

wherein, For the center wavelength of the FGB,Is the effective refractive index of the fiber mode,Is the period of FGB.

When stress is applied to the fiber, it causes a change in the radius and length of the fiber, which in turn causes a change in the grating period and effective refractive index. At this time, the FBG center wavelength variationCan be represented by the following formula (2):

（2）

wherein, For the radial strain of the FBG,As the diameter variation of the FBG,Is the elasto-optical effect of the optical fiber,As a result of the waveguide effect of the optical fiber,In order to derive the sign of the deviation,Is the diameter of the FBG,Is the effective package length of the FBG.

The relative change of the wavelength of the FBG under the action of axial stressCan be represented by the following formula (3):

（3）

Wherein Deltalambda _B is the central wavelength variation of the FBG, For the axial strain of the optical fiber,To be effective in the elastance, for fused silica fiber, the elastance is

The acceleration sensor can be regarded as an inertial acceleration sensor, when an acceleration excitation signal is outsideActing on the inertial mass will cause the inertial mass to shift from the equilibrium position. The external signal is a continuous sine signalWhereinFor the amplitude of the vibration signal,Is the angular frequency of the vibration signal. According to the theory of inertia, the displacement motion equation of the inertial body can be expressed by the following equation (4):

（4）

wherein, In order to derive the sign of the symbol,For displacement of the inertial body from the equilibrium position,Is the mass of the inertial body, and the mass of the inertial body,For the damping of the system, _eff For the equivalent stiffness of the system,Is the time of the time domain signal.

Amplitude of systemCan be represented by the following formula (5):

（5）

Wherein the method comprises the steps of As a damping ratio of the system,For the angular frequency of the system,In the form of a frequency ratio,For the acceleration signal received by the sensor.

As known from Newton's law, when the external acceleration signal changes, the acceleration signalCan be represented by the following formula (6):

（6）

wherein, In order for the forces to act on the system,As the variation of the FBG,Is equivalent stiffness of the sensor.

The sensitivity of the FBG acceleration sensor is defined as the variation of the center wavelength of the FBGAnd (3) withCan be expressed by the following formula (7):

（7）

The sensitivity of the FBG accelerometer can be obtained by combining the formulas (3), (5) and (6) described above, and can be expressed by the following formula (8):

（8）

When the frequency ratio tends to 0, the ideal acceleration sensitivity in the above equation (8) can be expressed by the following equation (9):

（9）

The resonant frequency expression of the sensor can be obtained according to the vibration principle, and can be expressed by the following formula (10):

（10）

Wherein the sensor has equivalent stiffness This can be expressed by the following formula (11):

（11）

wherein, The stiffness of the influence of the orthogonal direction on the main vibration direction,Is the rigidity of the elastic structure in the main vibration direction,Is the fiber stiffness in three directions.

In some embodiments, in order to verify the detection effect of the acceleration sensor, the embodiment of the present invention performs an experiment on the acceleration sensor, which specifically includes:

1) Amplitude-frequency characteristic experiment:

The amplitude-frequency characteristic is one of response characteristic parameters of the FBG accelerometer, and can reflect the resonance frequency, the flat area, the working frequency band and the flat area sensitivity of the accelerometer. In the amplitude-frequency response experiment of the sensor, the embodiment of the invention takes the example of applying 0.5g of acceleration to the sensor at different frequencies, and then obtaining the wavelength drift amount when the same acceleration signals are obtained at different frequencies, so that the amplitude-frequency characteristic curve of the sensor is shown in figure 5. Fig. 5 is a schematic diagram of amplitude-frequency characteristics of an acceleration sensor according to an embodiment of the present invention, and referring to fig. 5, the flat areas in three directions are approximately the same, and it can be determined that the flat areas in the X, Y, Z direction of the sensor are 20 to 190hz,20 to 205hz, and 30 to 205hz, respectively, and the sensor can normally operate in this frequency range.

2) Linear sensitivity curve:

Sensitivity is the ratio between the output wavelength of the detector and the acceleration amplitude. In the linear sensitivity experiment of the sensor, the embodiment of the invention takes the wavelength change at 100Hz in three directions as an example, wherein the acceleration peak value of the sensor is taken as an output signal, the amplitude of the acceleration sensor is increased from 0.2G to 3.0G by taking 0.2G as a step length, and the linear relation between the wavelength peak value change of the sensor and the acceleration signal can be shown as a figure 6. Fig. 6 is a schematic diagram of linearity curve of an acceleration sensor according to an embodiment of the present invention, where fig. 6 shows that the sensor has a good linearity relation, and the sensitivity in the X direction is 168pm/G (R ² =0.998), the sensitivity in the Y direction is 158pm/G (R ² =0.999), and the sensitivity in the Z direction is 133pm/G (R ² =0.999) at a frequency of 150 Hz.

3) Time domain waveform profile:

Referring to fig. 7, 8 and 9, fig. 7 is a time domain waveform diagram of the acceleration sensor of the present invention in the X direction of the sensor at 200Hz, fig. 8 is a time domain waveform diagram of the acceleration sensor of the present invention in the Y direction of the sensor at 200Hz, and fig. 9 is a time domain waveform diagram of the acceleration sensor of the present invention in the Z direction of the sensor at 200 Hz. The waveform of the sensor X, Y, Z at 200Hz is a perfect sine curve, which is consistent with the waveform of the input signal of the vibrating table, so that the linearity of the input and output signals of the sensor is good.

In the embodiment of the invention, firstly, the elastic structures of the six surfaces of the elastic body frame adopt four diamond structures as the sensitive elements of the vibration signals, and the sensitive elements can well concentrate the strain areas on the elastic structures, so that compared with the straight beams, hinges, multi-beams and the like of other three-dimensional sensors, the sensitivity of the sensor can be improved, and the boundary effect can be reduced, so that the vibration signals can be well received.

In addition, the embodiment of the invention adopts one inertial mass block, compared with other three-dimensional sensors with multiple inertial mass blocks, the problem of inconsistent mass centers of the multiple mass blocks can be avoided by adopting one inertial mass block, so that three-dimensional signals are more accurately collected, the three-direction resonance frequency and the sensitivity are approximately the same, the problem that the sensor is easily damaged due to overlarge sensitivity in one direction in use of the traditional three-dimensional sensor is avoided, and the stability of the sensor is enhanced.

In addition, an inertial mass block is adopted to integrate the elastic bodies in three directions, so that the volume of the sensor is greatly reduced. Since the resonance frequencies and the sensitivities in the three directions are nearly identical, the directivity of the sensor is not strict in actual installation and use, and any one surface can be used as the main vibration direction, so great convenience is brought in actual use.

Finally, the grating in the embodiment of the invention adopts two-point type packaging, so that the packaging process of the optical fiber is greatly simplified, and the problem that the whole-adhesion type packaging can cause the chirp effect of the grating is avoided. Because the sensor frame adopts cubes and the elastic bodies are symmetrical, compared with the grating in three directions of the split three-dimensional sensor, the orthogonal state is easier to find, and the three optical fibers are mutually orthogonal, so that signals received in the cross direction and the main vibration direction are in a sine angle relation, and when the signals are received in the main vibration direction of the sensor, the sensor can effectively avoid sensitivity in other directions, and therefore, the sensor has strong transverse interference resistance.

In this specification, each embodiment is described in a progressive manner, and the same or similar parts of each embodiment are referred to each other, and each embodiment is mainly described as a difference from other embodiments.

The above embodiments are only for illustrating the technical solution of the present application, and not for limiting the present application; although the application has been described in detail with reference to the foregoing embodiments, it will be understood by those of ordinary skill in the art that: the technical scheme described in the foregoing embodiments can be modified or some or all of the technical features thereof can be replaced with equivalents; such modifications and substitutions do not depart from the spirit of the application.

Claims

1. A fiber grating three-dimensional vector acceleration sensor, comprising: an integrated core structure, a shell and a fiber grating; the core body structure and the shell are both of a square structure, and the core body structure is supported and fixed at the center of the shell through a first fixing structure;

The core structure comprises an elastomer frame, an inertial mass block of a cube structure and elastic structures respectively arranged on six surfaces of the elastomer frame; the parameters of the elastic structures are the same, a through hole is formed in the center of each elastic structure, and a second fixing structure fixes the inertial mass block at the center of the elastic body frame through the through holes;

One side surface of each elastic structure facing the shell is provided with one fiber bragg grating, and the central axes of any two fiber bragg gratings in the three fiber bragg gratings are different-plane straight lines and mutually orthogonal.

2. The acceleration sensor of claim 1, characterized in, that the elastic structure comprises four diamond-shaped structures, four of which constitute a symmetrical structure, the through hole being arranged in the center of the intersection of the four diamond-shaped structures.

3. The acceleration sensor of claim 2, wherein the fiber grating is fixed to the surface of the elastic structure by a two-point package, and the fiber grating is fixed to the second fixing structure at one end and to the elastic body frame at the other end along a diagonal line of the diamond structure.

4. The acceleration sensor of claim 1, characterized in, that the first fixation structure comprises fixation buckles arranged at eight vertex positions of the elastomer frame, the fixation buckles being of the same material as the core structure.

5. The acceleration sensor of claim 1, characterized in, that the second fixation structure comprises a single-pass hexagonal copper pillar and a corresponding screw arranged in the center of each elastic structure, and that each face center of the inertial mass is provided with a threaded hole; the bottom of the single-pass hexagonal copper column is fixed in a threaded hole in the center of the inertial mass block, and one end with threads of the screw penetrates through the through hole of the elastic structure and is in threaded connection with the top of the single-pass hexagonal copper column.

6. The acceleration sensor of claim 1, wherein the elastomer frame, the elastic structure, and the inertial mass are all made of brass.

7. The acceleration sensor according to claim 1, characterized in that the parameters of each of the fiber gratings are the same, and the fiber gratings are pre-stressed so that the amount of change in the center wavelength of the fiber grating satisfies a preset condition.

8. The acceleration sensor of claim 1, wherein the housing is provided with a fiber outlet hole in the center of each of three surfaces corresponding to the fiber bragg grating, for guiding out the fiber bragg grating, so that the fiber bragg grating is connected to an external adjusting unit.

9. The acceleration sensor of claim 8, wherein the fiber-outlet holes are cured by glue sealing.