Plate type optical fiber accelerometer of multi-layer turn special-shaped optical fiber ring

Abstract

The invention discloses a plate-type optical fiber accelerometer of a multi-layer-turn special-shaped optical fiber ring. The plate-type optical fiber accelerometer comprises a probe, an interference light path and a demodulation system. Wherein the probe part is formed by bonding a plurality of special-shaped optical fiber rings on a rectangular thin plate, the optical fiber rings are arranged in a multi-layer turn closest packing mode, and the shapes of the optical fiber rings include but are not limited to runway shapes, ellipses or rounded rectangles; the interference light path part adopts a Michelson interferometer or a Mach-Zehnder interferometer; and the demodulation system part comprises a photoelectric converter, an acquisition card and a data processing board, and the interfered signal is processed by adopting a phase generated carrier (PGC) method. The beneficial effects of the invention are that the plate-type optical fiber accelerometer composed of the special-shaped optical fiber rings is invented, and a general method for performing performance calculation is provided for the accelerometer; a traditional circular optical fiber ring is replaced by the special-shaped optical fiber ring, so that the sensitivity of the sensor is improved on the premise that the optical fiber length of the sensor is the same and the resonant frequency is kept unchanged; meanwhile, the optical fiber thermal noise levels under the same optical fiber length are roughly the same, and the improvement of the sensitivity means the improvement of the overall signal-to-noise ratio.

Description

Technical Field

[0001] The invention relates to the technical field of optical fiber accelerometers, and in particular to a plate-type accelerometer of a multi-layer turn special-shaped optical fiber ring. Background Art

[0002] The currently commonly used mandrel-type or disk-type fiber optic accelerometers usually have a higher resonant frequency due to their own structural characteristics, but their detection performance in the low frequency band is often poor. Therefore, the present invention designs a multi-layer turn special-shaped fiber optic ring accelerometer based on a rectangular thin plate structure to improve the detection performance of this type of accelerometer in the low frequency band and increase the design flexibility. Summary of the invention

[0003] The purpose of the present invention is to solve the problem that the existing fiber optic accelerometer has insufficient detection performance in the low frequency band, and proposes a plate-type fiber optic accelerometer with multiple turns of special-shaped fiber optic rings for measuring acceleration information in the low frequency band.

[0004] The technical solution adopted by the present invention to solve the above technical problems is as follows: the present invention comprises a probe module, an interferometer module and a signal demodulation module together forming a complete system, which is described in detail as follows.

[0005] The probe module described in the above scheme is characterized in that a rectangular thin plate structure with a larger surface area is used so that the probe can better receive low-frequency signals, and the multi-layer fiber ring makes the probe have higher sensitivity and thus a higher signal-to-noise ratio. The upper and lower sides of the rectangular thin plate are connected by stainless steel pins or springs. When the pins are used for fixing, the set of equipment has the maximum detection upper limit, but the sensitivity is at the minimum value at the same time; when the spring is used to connect the rectangular thin plate and the frame, the sensitivity and detection upper limit of the probe can be freely adjusted by adjusting the spring stiffness coefficient. The fiber ring located on the rectangular thin plate adopts a non-circular special-shaped fiber ring, including but not limited to a runway shape, an ellipse or a rounded rectangle. Theoretical calculations show that this type of fiber ring can further improve the sensitivity index of the probe compared to the traditional circular fiber ring. The fiber ring is wound by a single-mode fiber with a core / cladding diameter of 80 / 135 microns or a panda polarization-maintaining fiber with a specification of 80 / 135 microns. In addition, the above-mentioned special-shaped fiber rings are bonded to both the front and back sides of the rectangular thin plate to form a push-pull structure, and this pair of fiber rings are respectively located at the two arms of the interferometer module.

[0006] The interferometer module described in the above scheme is characterized by using a Michelson interferometer structure or a Mach-Zehnder interferometer structure, wherein the two arms of the interferometer are composed of sensor probes. The light source selected for the optical path is a laser with a wavelength of 1310nm or 1550nm.

[0007] The demodulation system module described in the above scheme is characterized by being composed of a photoelectric converter, a phase generated carrier (PGC) demodulation board and a data acquisition board. The photoelectric converter converts the optical signal output by the interferometer into an electrical signal, and after the phase signal is demodulated by the differential and PGC demodulation board, the data acquisition board collects the data and the host computer displays the signal to display the measured acceleration signal.

[0008] According to the above scheme, the multi-layer turn special-shaped fiber ring plate accelerometer is characterized by using a scheme of bonding several multi-layer turn special-shaped fiber rings on a large-sized rectangular thin plate to detect low-frequency acceleration signals, while ensuring its high sensitivity index; the rectangular thin plate is fixed by a pin or spring connection method, and the flexible connection method allows the accelerometer to freely adjust the detection range and probe sensitivity according to demand. After sensing the external acceleration information, the probe part generates an interference signal at the interferometer, and the demodulation system demodulates the interference signal to finally obtain the external acceleration information. Due to the use of the interferometric measurement scheme, this accelerometer has extremely high sensitivity and low cost advantages, and is an excellent solution for measuring low-frequency acceleration.

[0009] The beneficial effects of the present invention are as follows: a plate-type fiber optic accelerometer composed of a special-shaped fiber optic ring is proposed, and a general method for calculating the performance of the accelerometer is proposed; a solution of using a special-shaped fiber optic ring to replace the traditional circular fiber optic ring is proposed, so that the sensor can improve the sensitivity performance of the sensor under the premise of the same fiber length and keeping the resonant frequency unchanged. At the same time, the design of the plate structure and the adjustable spring allows the sensor to detect lower frequency signals. The entire solution from the vibration pickup structure to the sensing optical path to the inversion of vibration information is proposed, and the entire detection device is fully constructed through the three modules of the probe module, the interference optical path module and the demodulation system. BRIEF DESCRIPTION OF THE DRAWINGS

[0010] Figure 1 It is a design scheme diagram of the present invention.

[0011] Figure 2 Schematic diagram of the probe structure in this embodiment.

[0012] Figure 3 Schematic diagram of the interference light path in this embodiment.

[0013] Figure 4 FIG. 4 is an algorithm flow chart of the demodulation system in this embodiment.

[0014] Among them: 1. Probe module; 2. Interference optical path module; 3. Demodulation system module; 4. Stainless steel frame; 5. Rectangular thin plate; 6. Multi-layer turn special-shaped optical fiber ring; 7. Fixed pin or spring; 8. Vibration source; 9. First light source; 10. 2×2 single-mode coupler (splitting ratio is 50:50); 11. Piezoelectric ceramics; 12. First Faraday rotator; 13. Second Faraday rotator; 14. First photoelectric converter; 15. PGC demodulation board; 16. Digital Data acquisition board; 17, computer; 18, first probe; 19, second light source; 20, Y waveguide; 21, second probe; 22, 2×2 polarization-maintaining coupler (splitting ratio is 50:50); 23, second photoelectric converter; 24, third photoelectric converter; 25, first multiplier; 26, second multiplier; 27, first low-pass filter; 28, second low-pass filter; 29, divider; 30, inverse tangent operation module; 31, high-pass filter. DETAILED DESCRIPTION

[0015] In order to make the purpose, technical solution and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

[0016] like Figure 1 , Figure 2 , Figure 3 and Figure 4 The plate-type fiber optic accelerometer of a multi-layer turn special-shaped fiber ring shown in the figure is composed of a probe module 1, an interferometer module 2 and a demodulation system module 3. The probe module 1 includes a stainless steel frame 4, a transducer rectangular thin plate 5, a multi-layer turn special-shaped fiber ring 6 and a fixed pin or spring 7; the interferometer module 2 is divided into two schemes: Scheme 1 is a Michelson interferometer scheme, and Scheme 2 is a Mach-Zehnder interferometer scheme, wherein Scheme 1 includes a first light source 9, a 2×2 single-mode coupler (splitting ratio is 50:50) 10, a first probe 18, a piezoelectric ceramic 11, a first Faraday rotator 12, a second Faraday rotator 13 and a photoelectric converter 14, and Scheme 2 includes a second light source 19, a Y waveguide 20, a second probe 2 1. 2×2 polarization-maintaining coupler (splitting ratio is 50:50) 22, a first photoelectric converter 23 and a second photoelectric converter 24; the demodulation algorithm process in the demodulation system module is that the interference signal is subjected to a first multiplier 25 and a second multiplier 26 for mixing processing of frequency doubling and frequency doubling respectively, and then the high-frequency components are filtered out by a first low-pass filter 27 and a second low-pass filter 28 respectively, and then the two signals are divided by a divider 29, and the calculated signal is then passed through an inverse tangent operation module 30 and a high-pass filter 31 to invert the phase change.

[0017] Preferably, the probe module 1 and the interferometer module 2 are a whole, and together constitute a complete optical path. The surface of the rectangular thin plate 5 is flat, without bending, and relatively rough so that the optical fiber ring 6 can be firmly bonded; the optical fiber ring 6 adopts a multi-layer winding method, and the shape is preferably a runway shape to obtain maximum sensitivity. When the Michelson interferometer scheme is adopted, the optical fiber is preferably a single-mode optical fiber with a core / cladding diameter of 80 / 135 microns, and when the Mach-Zehnder interferometer is adopted, a panda polarization-maintaining optical fiber of 80 / 135 microns is preferably used; the thin plate 5 is preferably fixed with a pin 7, at which time the sensor has a maximum detection upper limit. When higher sensitivity requirements are required, it is preferred to use a spring to replace the pin 4 to obtain higher sensitivity.

[0018] Preferably, the interference optical path adopts the Michelson interferometer solution, which can use single-mode devices and single-mode optical fibers, making the whole set of equipment low-cost. The first light source 9 uses a 1550nm laser. After passing through the 2×2 single-mode coupler 10, the light wave is evenly divided into two parts and enters the first probe 18 and the optical fiber wrapped around the piezoelectric ceramic 11 respectively. The two paths of light pass through the first Faraday rotator 12 and the second Faraday rotator 13 respectively and re-enter the 2×2 single-mode coupler 10 and interfere. The interference signal is finally converted into an electrical signal by the first photoelectric converter 14. In this process, the acceleration signal generated by the vibration source 8 is captured by the first probe 18, and causes the rectangular thin plate 5 and the optical fiber ring 6 to deform, thereby causing the phase of the light transmitted in the optical fiber to change. The change carries the acceleration information of the outside world and is inverted in the demodulation system. In scenarios where higher sensitivity is required, the Mach-Zehnder interferometer is preferred. The optical fiber ring 6 must be bonded to both the front and back sides of the rectangular thin plate 5 to form a push-pull structure. In the optical path design, the two optical fiber rings 6 are respectively connected to the sensing arm and the reference arm of the Mach-Zehnder interferometer, and the second photoelectric converter 23 and the third photoelectric converter 24 are used at the end of the optical path to convert the two optical signals into electrical signals. Theoretical proof that when this solution is adopted, the system has twice the sensitivity compared to the Michelson interferometer solution, but at the same time, the devices in the optical path need to be replaced with full polarization-maintaining devices, and the optical fiber ring 6 also needs to be wound with panda polarization-maintaining fiber.

[0019] Preferably, the demodulation scheme in the demodulation system adopts a phase generated carrier inverse tangent method (PGC-Arctan) demodulation method. Compared with the phase generated carrier differential cross multiplication method (PGC-DCM) demodulation method, this method has a simpler structure, thereby reducing the signal processing time. At the same time, the PGC-Arctan demodulation method is not sensitive to light intensity interference.

[0020] Preferably, the fiber optic accelerometer proposed in the present invention can be used not only on land, but also in marine environments when anti-corrosion materials are used.

[0021] According to the above scheme, the sensitivity calculation method of the sensor is:

[0022] When a length of optical fiber L is subjected to external disturbance, the phase change can be expressed as

[0023]

[0024] Where β is the wave number, n 0 is the refractive index of the fiber core, ν is the Poisson's ratio of the fiber, and p 11 and p 12 is the elastic-optical coefficient, ε θ is the axial strain of the optical fiber. The sensitivity of the interferometric fiber accelerometer is defined as the phase change under unit acceleration. A represents the acceleration of the accelerometer. According to the definition, the sensitivity S of the fiber optic accelerometer can be expressed as:

[0025]

[0026] For fiber rings of different shapes, different spaces can be established to calculate the tangential strain of the fiber ring. According to the tensor analysis theory, the tangential strain of the fiber ring can be obtained as follows:

[0027]

[0028] A is composed of Calculation is performed to obtain, where are the components in Cartesian space and the newly established space respectively.

[0029] According to the above scheme, the resonant frequency of the sensor is calculated as follows:

[0030] The corresponding symbols of each parameter of the plate sensor are shown in the following table

[0031]

[0032] The displacement tolerance function w is determined as:

[0033]

[0034] Among them A mn are the unknown coefficients, M and N are the series cutoff coefficients, and f m (x) and g m (y) is a polynomial orthogonal in the x-direction and the y-direction, and its expression is as follows:

[0035]

[0036]

[0037] The Lagrangian functional of the system is:

[0038]

[0039] Where V p is the strain energy of the transducer plate, V s is the elastic potential energy of the spring, V pi is the strain energy of the missing circular hole, T is the kinetic energy of the transducer plate, T i is the kinetic energy of the missing circular hole, which is expressed as follows:

[0040]

[0041] Where D is:

[0042]

[0043]

[0044] According to Hamilton's principle:

[0045]

[0046] Substituting the Lagrange functional into the solution, the matrix equation is as follows:

[0047] (K-ω 2 M)A=0 (15)

[0048] The eigenvalue in the characteristic equation is the natural frequency of the transducer plate. Substituting the eigenvector corresponding to the eigenvalue into the displacement allowable function can obtain the vibration shape of the corresponding mode.

[0049] The above embodiments are only used to illustrate the design ideas and features of the present invention, and their purpose is to enable those skilled in the art to understand the content of the present invention and implement it accordingly. The protection scope of the present invention is not limited to the above embodiments. Therefore, any equivalent changes or modifications made based on the principles and design ideas disclosed by the present invention are within the protection scope of the present invention.

Claims

1. A plate-type optical fiber accelerometer with multi-layer turns of special-shaped optical fiber rings, characterized in that: It consists of three parts: probe, interference optical path and demodulation system. The probe part is composed of a structure in which several special-shaped optical fiber rings are bonded on a rectangular thin plate. The optical fiber rings are arranged in a multi-layer turn closest stacking manner, and their shapes include but are not limited to racetrack shape, ellipse or rounded rectangle; the interference optical path part adopts Michelson interferometer or Mach-Zehnder interferometer; the demodulation system part includes photoelectric converter, acquisition card and data processing board, and the phase information of the interfered signal is restored by the phase generated carrier (PGC) method.

2. The probe portion according to claim 1, characterized in that: The rectangular thin plate is made of metals such as stainless steel and copper or non-metallic materials such as carbon fiber, and its thickness does not exceed 1 cm; the optical fiber ring is bonded to one side or both sides of the rectangular thin plate. When located on both sides of the rectangular thin plate, the two optical fiber rings are symmetrical about the rectangular thin plate to form a push-pull structure; the outer side of the probe uses a metal frame made of stainless steel.

3. The optical fiber ring according to claim 2, characterized in that: A multi-layer turn closest stacking arrangement structure is adopted, with the number of turns in each layer being greater than or equal to 1, and the total length of the optical fiber ring is in the order of hundreds of meters to kilometers; the shape of the optical fiber ring includes but is not limited to a racetrack shape, an ellipse, a rounded rectangle or a circle; the optical fiber ring is wound with a single-mode optical fiber with a core / cladding diameter of 80 / 135 microns or a panda polarization-maintaining optical fiber with a specification of 80 / 135 microns.

4. The probe part according to claim 2, characterized in that: The optical fiber ring and the rectangular thin plate are bonded with epoxy resin glue.

5. The probe part according to claim 2, characterized in that: The rectangular thin plate and the probe frame are fixed by stainless steel pins or connected by springs, or connected by a combination of stainless steel pins and springs.

6. The interference optical path portion according to claim 1, characterized in that: A Michelson interferometer or a Mach-Zehnder interferometer is used. When a Michelson interferometer is used, the optical path is composed of a 2×2 single-mode coupler, a photoelectric converter, and two Faraday rotators. In order to demodulate the interference signal later, one arm of the optical path is also wrapped with piezoelectric ceramics; when a Mach-Zehnder interferometer is used, the optical path is composed of a multifunctional integrated optical waveguide modulator (Y waveguide), a 2×2 polarization-maintaining coupler, and two photoelectric converters.

7. The interference optical path portion according to claim 6, characterized in that: The probe part constitutes the sensing arm and reference arm of the interference optical path, and this part and the rest of the optical path together form a complete interferometer; the optical path adopts narrow linewidth laser, and the wavelength of the light wave is 1310nm or 1550nm.

8. The demodulation system part according to claim 1, characterized in that: It is composed of a photoelectric converter, an acquisition card and a data processing board. The interfered signal is processed using the phase generated carrier (PGC) method.

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