Optical fiber acceleration detector based on a trivariant cylinder and method for detecting vibration acceleration

Abstract

The application discloses a fiber acceleration detector based on a shape-variable cylinder and a method for detecting vibration acceleration. One end of the cylindrical shape-variable cylinder is used as a mounting end. Three axial grooves are arranged on the side wall of the shape-variable cylinder in a circumferential direction and are distributed at an angle of 120 degrees. An optical fiber with a certain pre-stress is fixed in each axial groove by using glue. A grating is engraved on the optical fiber. The shape-variable cylinder detector is mainly made of silica gel, is easy to deform, has good bending strain performance, and has higher sensitivity than common metal structures under the same conditions. The application has the advantages of convenient production, simple structure and accurate measurement.

Description

Technical Field

[0001] This invention belongs to the field of fiber optic sensing technology, specifically relating to a vibration acceleration detector. Background Technology

[0002] Faced with an increasingly severe energy security situation, the country has put forward the development requirement of "vigorously increasing oil and gas exploration and development efforts to ensure national energy security," making the improvement of petroleum exploration technology increasingly important. In the process of oil field exploration, seismic exploration is the most common method. This method requires artificially generating seismic waves, using precision devices to record the vibration signals of these waves, and then processing and analyzing the collected signals to locate oil-bearing structures.

[0003] Common vibration detectors are mainly classified into three types: mechanical, electrical, and optical. Due to the weak nature of seismic wave signals, the latter two types are commonly used for detection. Compared to traditional electrical detectors, optical detectors are more sensitive to vibration signals and have advantages such as small size, high sensitivity, high temperature resistance, and ease of use, making them more suitable for seismic detection.

[0004] Optical accelerometers can be broadly categorized by the type of fiber used: ordinary single-mode fiber optic accelerometers and multi-core fiber optic accelerometers. Multi-core fibers directly detect physical quantities using a single multi-core fiber; however, accelerometers based on multi-core fibers are expensive to manufacture and suffer from inter-core crosstalk. Single-mode fiber accelerometers rely on mechanical structures to form the sensing structure, but the manufacturing process for existing single-mode fiber accelerometers is complex and time-consuming. Therefore, there is an urgent need for a fiber optic accelerometer that is easy to manufacture, has a simple structure, and provides accurate measurements. Summary of the Invention

[0005] The technical problem to be solved by the present invention is to overcome the shortcomings of existing fiber optic accelerometers and provide a fiber optic accelerometer based on a conformal column with reasonable design, simple structure, simple manufacturing process, and high measurement accuracy, as well as a method for detecting vibration acceleration.

[0006] The technical solution adopted to solve the above technical problems is: a fiber optic accelerometer based on a compliant column. One end of the cylindrical compliant column is used as the mounting end. The side wall of the compliant column is provided with three axial grooves distributed at 120° along the circumference. An optical fiber with a certain prestress is fixed in each axial groove by adhesive. A grating is engraved on the optical fiber.

[0007] As a preferred technical solution, the surface of the optical fiber is coated with a silicone epoxy primer layer.

[0008] As a preferred technical solution, the grating has a grating area length of 2-5 mm and a center wavelength of 1500-1600 nm.

[0009] As a preferred technical solution, the diameter of the compliant column is 10-20 mm and the length is 65-100 mm, and the cross-section of the axial groove is semi-circular arc with a diameter of 1-2 mm.

[0010] As a preferred technical solution, the cis-converting column is obtained by mixing silicone and curing agent in a ratio of 100:3, injecting the mixture into a mold pre-coated with silicone oil, and allowing it to stand for 24 hours to cure.

[0011] As a preferred technical solution, the curing agent is organotin.

[0012] A method for detecting vibration acceleration using an optical fiber accelerometer based on a conformal column: The conformal column transmits the detected vibration signal to the gratings of three optical fibers, measures the center wavelength drift of the three gratings, determines the vibration direction based on the relationship between the geometric position of the three gratings and the wavelength drift, and then determines the acceleration value using the following formula;

[0013]

[0014] In the formula, a θ Let Δλ be the acceleration value. i This represents the wavelength shift corresponding to the i-th fiber, where i = 1, 2, 3, and S. i Let θ be the sensitivity of the calibrated i-th fiber, and θ be the azimuth angle of the vibration acceleration.

[0015] The azimuth angle θ of the vibration acceleration is:

[0016]

[0017] In the formula, Δλ1 is the wavelength shift of the first grating, Δλ2 is the wavelength shift of the second grating, and Δλ3 is the wavelength shift of the third grating.

[0018] The beneficial effects of this invention are as follows:

[0019] The conformal cylindrical detector in this invention is mainly made of silicone, which is easily deformable and has excellent bending strain performance. Under the same conditions, it has higher sensitivity than ordinary metal structures, with a maximum sensitivity of 608.91 pm / g in the flat region. Unlike the discrete structure of traditional three-component detectors, this detector concentrates the optical fibers on a single conformal cylinder, resulting in a smaller size. The diameter of the conformal cylinder is 10-20 mm, ensuring the detector's size while increasing the distance between different fiber cores, thus improving the detector's angular resolution. The three optical fibers in the detector are uniformly distributed at 120° on a single conformal cylinder. The magnitude and direction of acceleration, i.e., vector acceleration information, can be directly obtained from the changes in the center wavelengths of the three fiber gratings, enabling three-dimensional vector detection. Attached Figure Description

[0020] Figure 1 This is a schematic diagram of the structure of the present invention.

[0021] Figure 2 yes Figure 1 The right view.

[0022] Figure 3 This is a graph showing the test results of the detector's bending response.

[0023] Figure 4 This is the amplitude-frequency response diagram of the fiber optic accelerometer based on a compliant cylinder according to Embodiment 1 of the present invention.

[0024] Figure 5 This is the sensitivity response diagram of the fiber optic accelerometer based on a conformal column according to Embodiment 1 of the present invention at an operating frequency of 10Hz. Detailed Implementation

[0025] The present invention will be further described in detail below with reference to the accompanying drawings and embodiments, but the present invention is not limited to the following embodiments.

[0026] Example 1

[0027] exist Figure 1 , 2 This embodiment of an optical fiber accelerometer based on a conformal column consists of a conformal column 1, a first optical fiber 2, a second optical fiber 3, and a third optical fiber 4 connected together. The conformal column 1 is cylindrical, with a diameter of 15mm and a length of 80mm. One end of the conformal column 1 serves as the mounting end. Three axial grooves distributed at 120° along the circumference of the sidewall are provided. The cross-section of the axial groove is semi-circular arc with a diameter of 1.5mm. The surfaces of the first optical fiber 2, the second optical fiber 3, and the third optical fiber 4 are all coated with a silicone epoxy primer layer 5. The first optical fiber 2, the second optical fiber 3, and the third optical fiber 4 are placed in the three axial grooves in sequence and a certain prestress is applied. Then, they are fixed with silicone water. The silicone water and the silicone epoxy primer layer 5 of the optical fiber bond together, which improves the stability of the optical fiber. The first optical fiber 2, the second optical fiber 3, and the third optical fiber 4 are all engraved with gratings at a position 35mm away from the installation end. They are the first grating, the second grating, and the third grating, respectively. The grating area length of the first grating, the second grating, and the third grating is the same, which is 3mm, and the center wavelength is the same, which is 1580nm.

[0028] The cis-converting column 1 in this embodiment is obtained by mixing silicone and curing agent in a ratio of 100:3, injecting the mixture into a mold pre-coated with silicone oil, and allowing it to stand for 24 hours to cure. The curing agent is organotin. The cis-converting column 1 in this embodiment is easy to manufacture and has a simple process.

[0029] The method for detecting vibration acceleration based on the fiber optic accelerometer of the compliant column 1 in this embodiment is as follows: the compliant column 1 transmits the detected vibration signal to the gratings of the three optical fibers, measures the center wavelength drift of the three gratings, determines the vibration direction based on the relationship between the geometric position of the three gratings and the wavelength drift, and then determines the acceleration value by the following formula.

[0030]

[0031] In the formula, a θ Let Δλ be the acceleration value. i This represents the wavelength shift corresponding to the i-th fiber, where i = 1, 2, 3, and S. i Let θ be the sensitivity of the calibrated i-th fiber, and θ be the azimuth angle of the vibration acceleration.

[0032] The azimuth angle θ of the vibration acceleration is:

[0033]

[0034] In the formula, Δλ1 is the wavelength shift of the first grating, Δλ2 is the wavelength shift of the second grating, and Δλ3 is the wavelength shift of the third grating.

[0035] Example 2

[0036] In this embodiment, the compliant column 1 is cylindrical with a diameter of 10 mm and a length of 65 mm. One end of the compliant column 1 serves as the mounting end. The sidewall of the compliant column 1 has three axial grooves distributed at 120° along the circumferential direction. The cross-section of the axial grooves is semi-circular and has a diameter of 1 mm. The surfaces of the first optical fiber 2, the second optical fiber 3, and the third optical fiber 4 are all coated with a silicone epoxy primer layer 5. The first optical fiber 2, the second optical fiber 3, and the third optical fiber 4 are placed in the three axial grooves in sequence and a certain prestress is applied. Then, they are fixed with silicone water. The silicone water and the silicone epoxy primer layer 5 of the optical fiber bond together, which improves the stability of the optical fiber. The first optical fiber 2, the second optical fiber 3, and the third optical fiber 4 are all engraved with gratings at a position 35 mm away from the mounting end. These are the first grating, the second grating, and the third grating, respectively. The grating area length of the first grating, the second grating, and the third grating is the same, which is 2 mm, and the center wavelength is the same, which is 1500 nm.

[0037] The method for manufacturing the compliant column 1 and the method for detecting vibration acceleration using an optical fiber accelerometer based on the compliant column in this embodiment are the same as in Embodiment 1.

[0038] Example 3

[0039] In this embodiment, the compliant column 1 is cylindrical with a diameter of 20mm and a length of 100mm. One end of the compliant column serves as the mounting end. The sidewall of the compliant column has three axial grooves distributed at 120° along the circumference. The cross-section of the axial grooves is semi-circular and has a diameter of 2mm. The surfaces of the first optical fiber 2, the second optical fiber 3, and the third optical fiber 4 are all coated with a silicone epoxy primer layer 5. The first optical fiber 2, the second optical fiber 3, and the third optical fiber 4 are placed in the three axial grooves in sequence and a certain prestress is applied. Then, they are fixed with silicone water. The silicone water and the silicone epoxy primer layer 5 of the optical fiber bond together, which improves the stability of the optical fiber. The first optical fiber 2, the second optical fiber 3, and the third optical fiber 4 are all engraved with gratings at a position 35mm away from the mounting end. These are the first grating, the second grating, and the third grating, respectively. The grating area length of the first grating, the second grating, and the third grating is the same, which is 5mm, and the center wavelength is the same, which is 1600nm.

[0040] The method for fabricating the compliant column and the method for detecting vibration acceleration using an optical fiber accelerometer based on the compliant column in this embodiment are the same as in Embodiment 1.

[0041] experiment

[0042] To verify the beneficial effects of the present invention, the inventors used the fiber optic accelerometer based on the compliant cylinder of Example 1 to conduct bending response tests and vibration response tests.

[0043] 1. Bending response test

[0044] The fiber optic accelerometer based on the conformal column of Example 1 is fixed on a vertical displacement stage, allowing it to hang naturally. A horizontal displacement stage is pushed until its front end just contacts the conformal column of the detector. The displacement stage is continued to be pushed, causing the conformal column of the detector to bend. One end of the detector's fiber optic cable connected to the jumper is connected to an SM125 demodulator. The horizontal displacement stage is then pushed, and the center wavelength drift of the three fibers is detected at different displacement points. Figure 3 The first optical fiber is located directly in front of the displacement stage, where the bending degree is the greatest, and the center wavelength drift can reach 2.56nm. This indicates that the detector has good bending deformation and can obtain a large bending sensitivity, that is, static sensitivity. Therefore, the dynamic sensitivity is also improved accordingly.

[0045] 2. Vibration response test

[0046] The fiber optic accelerometer based on a conformal cylinder from Example 1 was mounted on a vibration table, allowing it to hang naturally. One end of the detector's fiber optic cable, connected to a jumper wire, was connected to a Si255 demodulator. A specific acceleration magnitude was set, and different frequency bands were selected for testing. The amplitude-frequency response curve of the detector was obtained, as shown below. Figure 4As shown, the resonant frequency of the detector is 21.4Hz, and its flat operating region is 0-14Hz, meaning the detector's operating frequency range is 0-14Hz. Sensitivity testing of the detector is performed at an operating frequency of 10Hz. Figure 5 When the third fiber is placed along the vibration direction, the strain is the largest, and the resulting sensitivity is 608.91 pm / g.

[0047] Therefore, the fiber optic accelerometer based on the compliant column of the present invention has higher sensitivity than ordinary metal structures under the same conditions because the compliant column is easy to deform and has good bending strain performance.

Claims

1. A fiber optic accelerometer based on a conformal cylinder, characterized in that: One end of the cylindrical compliant column serves as the mounting end. Three axial grooves distributed at 120° intervals are formed along the circumference of the column's sidewall. An optical fiber with a certain pre-stress is fixed within each groove using adhesive, and a grating is etched onto the fiber. The surface of the optical fiber is coated with a silicone epoxy primer layer. The compliant column is obtained by mixing silicone and a curing agent in a 100:3 ratio, injecting the mixture into a mold pre-coated with silicone oil, and allowing it to cure for 24 hours. The curing agent is organotin. The method for detecting vibration acceleration using the fiber optic accelerometer based on the conformal column is as follows: the conformal column transmits the detected vibration signal to the gratings of the three optical fibers, measures the center wavelength drift of the three gratings, determines the vibration direction based on the relationship between the geometric position of the three gratings and the wavelength drift, and then determines the acceleration value using the following formula. In the formula, This is the acceleration value. This corresponds to the wavelength shift of the i-th fiber. , Let θ be the sensitivity of the calibrated i-th fiber, and θ be the azimuth angle of the vibration acceleration. The azimuth angle θ of the vibration acceleration is: In the formula, This represents the wavelength shift of the first grating. This represents the wavelength shift of the second grating. This represents the wavelength shift of the third grating.

2. The fiber optic accelerometer based on a conformal cylinder according to claim 1, characterized in that: The grating has a grating area length of 2–5 mm and a center wavelength of 1500–1600 nm.

3. The fiber optic accelerometer based on a conformal cylinder according to claim 1, characterized in that: The diameter of the compliant column is 10-20 mm and the length is 65-100 mm. The cross-section of the axial groove is semi-circular and the diameter is 1-2 mm.

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