Fabry-Perot triaxial accelerometer based on optical fiber bending

Abstract

The invention discloses a Fabry-Perot triaxial accelerometer based on optical fiber bending. The Fabry-Perot triaxial accelerometer comprises a diaphragm, a diaphragm bracket, a ceramic ferrule, a metal center shaft, a metal shell and a 1 * 3 optical fiber coupler, the metal middle shaft part is provided with three embedded holes for placing the diaphragm supports, the three metal supports with the diaphragms are placed in the embedded holes, and the designed diaphragm placing direction angle is 120 degrees, so that the loss caused by optical fiber macro bending is reduced. And meanwhile, the optical fiber combining groove is designed, so that three paths of optical fibers in different directions can be combined in one direction through bending. The accelerometer is fixed on the surface of a measured object, when the diaphragms in three different directions vibrate, three relative cavity lengths can be changed, three peaks of a Fabry-Perot interference spectrum are demodulated, and the accelerations of the measured object in three directions can be measured. The diaphragm accelerometer has a wide application range, and the sensitivity and the working frequency band range can be adjusted by adjusting the parameters of the single diaphragm accelerometer.

Description

Technical Field

[0001] The invention belongs to the technical field of optical fiber optical measurement, and specifically discloses a Fabry-Perot three-axis accelerometer based on optical fiber bending. Background Art

[0002] Vibration has always been a key issue in the application of physics. In traditional measurement methods, electrical measuring instruments such as moving coil and piezoelectric are generally used, but electromagnetic interference has always been a difficult problem. As optical fiber is a medium for transmitting light, it has the characteristics of anti-electromagnetic interference, and the parameters of the light transmitted in the optical fiber (wavelength, frequency, polarization, amplitude, phase, etc.) can be used as the variation after sensing. Based on this, optical fiber vibration sensors with the advantages of anti-electromagnetic interference, high sensitivity, and long transmission distance can be produced.

[0003] At the same time, there is a wide demand for optical fiber vibration sensors in society, which have significant applications in industry, medical treatment, security and other fields.

[0004] In industry, fiber optic vibration sensors can test the performance of mechanical structures and monitor the health of structures. Since most mechanical equipment will produce vibration effects when working, using fiber optic vibration sensors to measure these vibration effects can reasonably judge the working conditions of mechanical equipment. At the same time, fiber optic vibration sensors can also be used in the medical field. Since many of human vital signs will reflect external vibration phenomena, many medical characteristics can be analyzed by measuring these vibration phenomena through fiber optic vibration sensors. Finally, fiber optic vibration sensors also have great application prospects in security aspects such as leak point monitoring and earthquake monitoring. Since pipeline leak points have different vibration characteristics, fiber optic vibration sensors can be used to judge leak points. In terms of earthquake monitoring, fiber optic vibration sensors can accurately measure the frequency and intensity of earthquakes, thereby determining the location and intensity of earthquakes.

[0005] The principle of the fiber optic triaxial accelerometer is similar to that of the uniaxial accelerometer. The mass block drives the diaphragm to vibrate and change the cavity length, thereby obtaining a changing interference spectrum. The acceleration value can be obtained by demodulating the interference spectrum. Based on this principle, Jing Han et al. studied an all-metal three-component fiber optic seismometer. In the 500Hz frequency band, the axial sensitivity of this sensor is about 41dB (0dB = 1rad / g), the fluctuation is ±2dB, and the lateral sensitivity is about -40dB. The sensor is made of metal, and winding the optical fiber on the metal structure can reduce the lateral cross sensitivity. Liang Xing et al. invented a well-permanent casing-outside three-component fiber optic MEMS seismic detector. Its elastic sensor chip is made of silicon-based etching and is a four-arm rotating structure. The acceleration range of the sensor after production is ±5g, the working range is 0-350Hz, and the sensitivity is high, but it is difficult to meet the requirements of miniaturization packaging.

[0006] Under the above circumstances, it becomes increasingly important to explore a fiber optic triaxial accelerometer that is miniaturized, easy to package, and has high stability. Summary of the invention

[0007] The present invention proposes a Fabry-Perot triaxial accelerometer based on optical fiber bending. The device obtains a miniaturized optical fiber triaxial accelerometer structure with good acceleration measurement performance by adding a certain macrobending loss.

[0008] In order to achieve the above object, the technical solution of the present invention is:

[0009] A Fabry-Perot triaxial accelerometer based on optical fiber bending, comprising an acceleration sensor, a metal center axis, a metal housing, and a 1×3 optical fiber coupler;

[0010] The metal shell is used to encapsulate the acceleration sensor, the metal center axis and the 1×3 optical fiber coupler; the acceleration sensor includes a diaphragm, a diaphragm bracket and a ceramic insert, the diaphragm is embedded in and fixed on the top of the diaphragm bracket; the ceramic insert is inserted from the lower end of the diaphragm bracket into the through hole in the center of the diaphragm bracket and fixed;

[0011] The metal center axis is a hollow cylindrical structure, with a circular hole channel for the optical fiber to pass through, and an embedded hole for carrying an acceleration sensor is also provided on the metal center axis; three metal center axes are arranged at three axial positions of the metal shell, and three bending grooves for bending the optical fiber are also provided in the metal shell, and the bending grooves are connected with the embedded holes through the circular hole channel of the metal center axis; the three optical fibers of the 1×3 optical fiber coupler are bent through the bending grooves and then inserted into the ceramic ferrules of the three acceleration sensors respectively; the end face of the optical fiber inserted into one end of the ceramic ferrule is arranged parallel to the diaphragm, thereby forming a Fabry-Perot cavity.

[0012] The present invention also provides a method for preparing the above-mentioned Fabry-Perot triaxial accelerometer based on optical fiber bending, comprising the following steps:

[0013] 1) The diaphragm bracket, the metal central shaft and the metal shell are made by laser cutting metal;

[0014] 2) Embed the diaphragm into the top of the diaphragm bracket, and insert the ceramic insert from the lower end of the diaphragm bracket into the through hole in the center of the diaphragm bracket to form an acceleration sensor;

[0015] 3) Install the metal center shaft to the three axial positions of the metal shell;

[0016] 4) Fix three acceleration sensors in the metal central axis, and bend the three optical fibers of the 1×3 optical fiber coupler through the bending groove and insert them into the ceramic ferrules of the three acceleration sensors respectively;

[0017] 5) Encapsulate the acceleration sensor, metal center axis and 1×3 optical fiber coupler with a metal shell.

[0018] Preferably, the diaphragm support, the metal central axis and the metal shell are made of titanium alloy plates by laser cutting, and have high strength and good corrosion resistance.

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

[0020] 1. Compared with the electrical three-axis accelerometer, the present invention has strong anti-electromagnetic interference capability and high reusability, and can also achieve high sensitivity and low-frequency measurement by changing the diaphragm structure.

[0021] 2. Compared with the optical three-axis accelerometer, the present invention has the characteristics of miniaturization and can work in miniaturized application scenarios.

[0022] 3. The metal body and the diaphragm support of the present invention are made of titanium alloy, which has high strength, good thermal properties and good corrosion resistance. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 This is a schematic diagram of the sensor structure in an embodiment of the present invention;

[0024] Figure 2 A schematic diagram of a sensitive membrane structure in an embodiment of the present invention;

[0025] Figure 3 A three-dimensional schematic diagram of a sensor support structure in an embodiment of the present invention;

[0026] Figure 4 is a three-dimensional schematic diagram of a metal central axis in an embodiment of the present invention;

[0027] Figure 5 Schematic diagram of coordinate transformation in an embodiment of the present invention;

[0028] Figure 6 The time domain waveform diagram of the present invention measured by applying 0.1g in the XYZ direction;

[0029] Figure 7 This is the single-axis sensitivity diagram of the three-axis sensor. DETAILED DESCRIPTION

[0030] The present invention is further described in detail below with reference to the accompanying drawings and embodiments:

[0031] The present invention provides a Fabry-Perot triaxial accelerometer based on optical fiber bending, the structure of which is as follows: Figure 1 and Figure 3As shown. The present invention proposes a Fabry-Perot triaxial accelerometer based on optical fiber bending, and its structure includes a diaphragm 1, a diaphragm bracket 2, a ceramic ferrule 3, a metal center axis 4, a metal housing 5, and a 1×3 optical fiber coupler 6. The diaphragm 1 and the diaphragm bracket 2 are used as sensitive elements as the core part of acceleration sensing. The metal center axis 4 is the core part of realizing the triaxial design.

[0032] The 1×3 fiber coupler is used to couple the interference light of the fiber optic accelerometer in three different directions. During production, the three coupling optical fibers, three diaphragm brackets, and three diaphragms of the 1×3 fiber coupler are directly made into a preliminarily connected three-axis accelerometer.

[0033] The metal shell encapsulates the metal central axis-accelerometer combination inside by screws, and the accelerometer pigtail and 1×3 optical fiber coupler are connected to the outside through the through hole of the metal shell. At the same time, the metal shell has four positioning holes for fixing the entire three-axis accelerometer on the surface of the object to be measured.

[0034] The diaphragm, diaphragm bracket and ceramic ferrule constitute the acceleration sensor. Figure 2 As shown, the diaphragm 1 is fixed on the diaphragm support 2 by three beams, the beam width is 0.2mm, the beam thickness is 8μm, and the beam gap is 0.2mm; the center thickness of the diaphragm 1 is 80μm, and the center circle radius is 0.9mm; one end of the ceramic ferrule 3 is inserted into the through hole in the center of the diaphragm support 2 and fixed, and the other end is inserted by a branch of the 1×3 optical fiber coupler 6 to form a Fabry-Perot cavity;

[0035] The metal central axis 4 is used to carry three acceleration sensors made of diaphragm brackets and fix the two together by welding. At the same time, a bending groove for bending optical fibers is designed in the metal shell 5 to bend the three optical fibers and fix them in the same direction.

[0036] like Figure 4 As shown, the metal center axis 4 is used to carry the acceleration sensors in three directions, and the limiting holes at the bottom are used to bend the optical fibers in three directions to one direction. In a specific embodiment of the present invention, the coordinate system where the three acceleration sensors are located, wherein the angle between the two coordinate axes of the horizontal coordinate system is 120°. The metal shell 5 is used to encapsulate the entire structure, and has four positioning holes thereon so that the sensor can be fixed on the surface of the measured object.

[0037] In a specific embodiment of the present invention, the diaphragm support, the metal central shaft, and the metal shell are made of titanium alloy plates by laser cutting.

[0038] The present invention also provides a method for preparing the above-mentioned Fabry-Perot triaxial accelerometer based on optical fiber bending, comprising the following steps:

[0039] 1) The diaphragm bracket, the metal central shaft and the metal shell are made by laser cutting metal;

[0040] 2) Embed the diaphragm into the top of the diaphragm bracket, and insert the ceramic insert from the lower end of the diaphragm bracket into the through hole in the center of the diaphragm bracket to form an acceleration sensor;

[0041] 3) Install the metal center shaft to the three axial positions of the metal shell;

[0042] 4) Fix three acceleration sensors in the metal central axis, and bend the three optical fibers of the 1×3 optical fiber coupler through the bending groove and insert them into the ceramic ferrules of the three acceleration sensors respectively;

[0043] 5) Encapsulate the acceleration sensor, metal center axis and 1×3 optical fiber coupler with a metal shell.

[0044] Preferably, the diaphragm support, the metal central axis and the metal shell are made of titanium alloy plates by laser cutting, and have high strength and good corrosion resistance.

[0045] The present invention measures acceleration based on the principle of multi-beam interference. Figure 1 As shown in the figure, assuming that a monochromatic light beam is incident, when the light passes through the end face of the optical fiber, end face reflection occurs, and part of the light is reflected again when it is transmitted to the sensitive film and coupled back to the optical fiber, and the two reflected lights form interference; similarly, the other films are the same. Therefore, the reflected light from the two end faces is reflected back to form an interference phenomenon, and the interference formula is as follows:

[0046]

[0047]

[0048] In the formula, R 1 , R 2 are reflectivity, Δ is phase difference, n is interference order, l is cavity length, and λ is light wavelength.

[0049] When the diaphragm vibrates, the cavity length l will change, causing changes in the interference spectrum. For physical analysis of this structure, it can be assumed that the mass of the mass block is uniformly distributed, and the effects of external damping and spring damping on the system are linear. When the external vibration excitation is a single-frequency vibration, the following equation can be written:

[0050] Where K is the total stiffness of the system, C is the damping of the system, y(t) is the excitation signal of the acceleration of the inertial mass, and x(t) is the displacement of the offset equilibrium position.

[0051] y(t)=k sin(wt-α) (4)

[0052] k is the amplitude of the external excitation signal, and ω is the angular frequency of the excitation signal.

[0053] Solving this differential equation, we get:

[0054]

[0055] In the formula, is the natural angular frequency of the system, is the damping ratio, is the frequency ratio, and a is the sensor acceleration.

[0056] The above is the principle of uniaxial testing, and for a triaxial acceleration sensor, its sensing result can be regarded as the superposition of uniaxial accelerations in three directions. Since the vectors in three-dimensional space can be represented by any three linearly independent bases, and different base groups can be converted by multiplying a transition matrix. Therefore, the placement of the three uniaxial sensors is not unique, that is, the vectors in the three directions corresponding to them are linearly independent.

[0057] The directions of the settings of the present invention are shown in the figure. Through the following linear transformation, the accelerations in the following three directions can be obtained.

[0058] Since there is no coupling in the acceleration of the Z axis, we only discuss the situation of the X and Y planes, such as Figure 5 As shown, at this time:

[0059]

[0060] And because Z=Z`, the coordinates can be converted into a normal rectangular coordinate system.

[0061] At the same time, the cross-sensitivity problem, that is, the sensitivity offset caused by vibrations in different axes, should also be considered in the design of the three-axis accelerometer.

[0062] After correcting the coordinate axis through linear transformation, the acceleration components in three directions can be obtained, which are recorded as ```

[0063] g x ,g y ,g z .

[0064] For a single-axis sensor, the sensitivity of a single accelerometer is g. x ,g y ,g z , and the mutual cross-sensitivity g xy ,g xz ,g yx ,g yz ,g zx ,g zy Can all be measured.

[0065] At this point, the equations can be obtained as follows:

[0066]

[0067] The result obtained after solving the equation is the sensed acceleration after eliminating cross sensitivity.

[0068] In order to test and analyze the linear response of the triaxial accelerometer in this embodiment, a vibration experimental device is built, which is composed of a light source part, an acceleration sensing part, and a data acquisition and processing part. The light source part is composed of a superluminescent diode (SLD) light source; the acceleration sensing part is composed of a vibration table that can realize three-dimensional vibration of different frequencies and accelerations and a Fabry-Perot triaxial accelerometer based on optical fiber bending designed by the present invention, and the data acquisition and processing part is realized by a phase spectrum demodulation module.

[0069] After the sensor is manufactured, an acceleration of 0.1g is applied in three directions, and the vibration frequency is 100Hz. The measured waveform is as follows: Figure 6 As shown, the vibration waveforms in the X and Z directions are directly Figure 7 By using the sensitivity demodulation, the acceleration in the X and Z directions can be measured to be 0.1g. For the acceleration in the Y direction, by using the above formula (6) for decoupling, the acceleration can be measured to be 0.1g, which is consistent with the actual applied acceleration.

[0070] Through experiments, it was found that the performance of the fiber optic accelerometer after the three-axis assembly was basically consistent with that of the uniaxial accelerometer, and the influence of fiber bending was basically negligible. The three-axis fiber optic vibration sensor designed by this invention is very small in size and very stable, and can be used for vibration testing in small spaces.

[0071] For the purpose of illustration and description, the present invention provides the aforementioned illustrative examples of the present invention. This is not intended to be an exhaustive description of the present invention or to limit the present invention to the precise form described, and modifications and changes can be made based on the above description. The embodiments are selected and described to explain the principles of the present invention and as a practical application of the present invention, so that those skilled in the art can use the present invention in various embodiments and make various modifications for specific purposes. All variations that can be directly derived or associated with the content disclosed by a person of ordinary skill in the art should be considered to be within the scope of protection of the present invention.

Claims

1. A Fabry-Perot triaxial accelerometer based on optical fiber bending, characterized in that: It includes an acceleration sensor, a metal central axis (4), a metal shell (5), and a 1×3 optical fiber coupler (6); The metal housing (5) is used to encapsulate the acceleration sensor, the metal center axis (4) and the 1×3 optical fiber coupler (6); The acceleration sensor comprises a diaphragm (1), a diaphragm support (2) and a ceramic insert (3); the diaphragm (1) is embedded in and fixed to the top of the diaphragm support (2); the ceramic insert (3) is inserted from the lower end of the diaphragm support (2) into the through hole in the center of the diaphragm support (2) and fixed; The metal center shaft (4) is a hollow cylindrical structure, with a circular hole channel for the optical fiber to pass through, and the metal center shaft (4) is also provided with an embedded hole for carrying an acceleration sensor; three metal center shafts (4) are arranged at three axial positions of the metal shell (5), and three bending grooves for bending the optical fiber are also provided in the metal shell (5), and the bending grooves are connected with the embedded hole through the circular hole channel of the metal center shaft (4); three optical fibers of the 1×3 optical fiber coupler (6) are bent through the bending grooves and then inserted into the ceramic ferrules (3) of the three acceleration sensors respectively; the end face of the optical fiber inserted into one end of the ceramic ferrule (3) is arranged parallel to the diaphragm, thereby forming a Fabry-Perot cavity.

2. The Fabry-Perot triaxial accelerometer based on optical fiber bending according to claim 1, characterized in that: The metal shell (5) of the accelerometer is fixed on the surface of the object to be measured to obtain vibration information of the object to be measured.

3. The Fabry-Perot triaxial accelerometer based on optical fiber bending according to claim 1, characterized in that: A coordinate system is established with acceleration sensors in three directions placed in the metal housing (5), wherein the angle between two coordinate axes of the plane coordinates is set to 120°, thereby reducing macrobending losses.

4. The Fabry-Perot triaxial accelerometer based on optical fiber bending according to claim 1, characterized in that: The diaphragm (1), diaphragm bracket (2), metal central axis (4) and metal shell (5) are made of titanium alloy plates by laser cutting.

5. The Fabry-Perot triaxial accelerometer based on optical fiber bending according to claim 1, characterized in that: The material of the diaphragm (1) is MEMS silicon nitride.

6. The Fabry-Perot triaxial accelerometer based on optical fiber bending according to claim 1, characterized in that: The metal shell is provided with a through hole, and the 1×3 optical fiber coupler is connected to the outside through the through hole of the metal shell.

7. A method for preparing a Fabry-Perot triaxial accelerometer based on optical fiber bending as claimed in claim 1, characterized in that: The following steps are involved: 1) A diaphragm support (2), a metal central axis (4) and a metal shell (5) are manufactured by laser cutting metal; 2) embedding the diaphragm (1) into the top of the diaphragm bracket (2), and inserting the ceramic insert (3) from the lower end of the diaphragm bracket (2) into the through hole in the center of the diaphragm bracket (2) to form an acceleration sensor; 3) Installing the metal center shaft (4) at three axial positions of the metal housing (5); 4) fixing three acceleration sensors in the metal central axis (4), and inserting three optical fibers of the 1×3 optical fiber coupler (6) into the ceramic ferrules (3) of the three acceleration sensors after bending through the bending grooves; 5) The acceleration sensor, the metal center axis (4) and the 1×3 optical fiber coupler (6) are packaged with a metal housing (5).

8. The preparation method according to claim 7, characterized in that: The metal shell encapsulates the acceleration sensor, the metal center axis (4) and the 1×3 optical fiber coupler (6) inside by means of screws.

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