Symmetric cylinder type optical fiber acceleration sensor based on uwDAS

Abstract

A compliant cylinder type optical fiber acceleration sensor based on an ultra-weak fiber Bragg grating (uwDAS) comprises an elastic body, a mass block and an optical fiber, the elastic body is of a tubular structure, the mass block is a cylinder with large mass and is fixed above the elastic body, and the optical fiber is tightly wound on the outer surface of the elastic body. During measurement, the elastic body is connected with a measured object, when external force acts on the measured object, the inertia effect causes the mass block to displace relative to the elastic body, the displacement causes the elastic body to deform, and then the optical fiber wound on the surface of the elastic body generates strain. The optical fiber strain causes the phase change of an internal reflected light signal, and the external acceleration is indirectly measured by monitoring and demodulating the phase change of the light signal. The optical fiber acceleration sensor has the advantages of simple structure, quick response, high sensitivity and the like, and is suitable for earthquake monitoring and application in related fields.

Description

Technical Field

[0001] The present invention relates to an optical fiber acceleration sensor, in particular to a compliant cylindrical optical fiber acceleration sensor based on ultra-weak fiber Bragg grating (uwDAS). Background Art

[0002] At present, traditional electrical microseismic monitoring equipment has been widely used in the industrial field. However, in practical applications, due to the limitations of its electrical working principle, electronic accelerometers are susceptible to electromagnetic interference when detecting microvibration signals, and when used in flammable and explosive coal mine environments, there are limitations in power supply safety and other aspects.

[0003] There are many deficiencies in the existing fiber optic accelerometers, which are mainly reflected in the structural design, frequency response range, sensitivity, material selection and application scenarios of the sensor. These deficiencies limit its effectiveness and performance in specific applications. According to existing research, the design structure of FBG accelerometers mainly includes different types such as mandrel type, diaphragm type, hinge type and cantilever beam type. Among them, the performance of the mandrel type sensor is significantly affected by the elasticity of the material, and there is a mutual restriction between stiffness and sensitivity, which leads to its insufficient ability in low-frequency signal measurement; the diaphragm type sensor is suitable for high-frequency environment, but it also performs poorly in low-frequency signal measurement; although the combined FBG sensor has advantages in frequency range and sensitivity, its complex structure leads to increased manufacturing and maintenance costs; the cantilever beam sensor is widely used due to its simple structure and high stability, but its resonant frequency limits its response ability in a variable vibration environment. In addition, the large volume of the sensor limits its application in space-constrained environments.

[0004] The Distributed Acoustic Sensing (DAS) system (uwDAS) based on ultra-weak fiber Bragg grating (uwFBG) uses the Fizeau interferometer principle to sense the strain or vibration signals acting on the optical fiber and realize multi-node distributed detection. This technology has the advantages of being passive, anti-electromagnetic interference and high precision. At the same time, a single optical fiber can support tens of thousands of sensing nodes, significantly improving the monitoring range and data collection density. More importantly, the uwDAS system can monitor vibration events along the line through a single optical cable, greatly reducing the difficulty and cost of deployment. Summary of the invention

[0005] In order to solve the above technical problems, the present invention proposes a compliant cylindrical fiber optic acceleration sensor based on ultra-weak fiber Bragg grating (uwDAS), which can realize high-precision, passive, and electromagnetic interference-resistant acceleration signal detection.

[0006] The technical solution adopted by the present invention is:

[0007] The uwDAS-based compliant cylindrical fiber optic acceleration sensor includes: an elastomer, a mass block, and a sensing fiber. The sensing fiber is tightly wound around the outer surface of the elastomer to sense the deformation caused by external signal excitation, thereby obtaining an acceleration signal; the mass block is fixed above the elastomer to form a fiber optic acceleration sensor.

[0008] The elastomer is a tubular structure with a relatively low Young's modulus, and as a sensitive material, it deforms under the stimulation of an external signal, thereby effectively transmitting external signal change information, such as an acceleration signal, to the sensing optical fiber wound on its outer surface.

[0009] The mass block is a cylindrical structure with a large mass. It generates displacement under the stimulation of external signals through its large inertial mass, so as to effectively transmit the external signals to the elastic body, thereby causing the elastic body to deform, and detect the acceleration signal through the sensing optical fiber; thereby enhancing the detection sensitivity of the acceleration signal.

[0010] The sensing optical fiber is a thin-diameter anti-bending optical fiber engraved with ultra-weak fiber gratings, and the optical fiber between two adjacent gratings is an independent sensing unit.

[0011] The mass block is fixedly connected to the elastic body by an adhesive, so as to ensure that the mass block is stably attached to the elastic body.

[0012] The mass of the mass block is much greater than the mass of the elastic body. When the sensor is stimulated by an external signal, the inertia of the mass block can effectively act on the elastic body to cause it to deform, thereby improving the response sensitivity of the sensor to the acceleration signal.

[0013] Based on the acceleration measurement method of the uwDAS-based compliant cylindrical fiber optic accelerometer, when the external excitation signal acts on the fiber optic accelerometer, the signal is transmitted to the mass block through the elastic body. According to Newton's second law (F=ma), the external force causes the mass block to generate acceleration, and the mass block is displaced relative to the elastic body. This displacement causes the elastic body to deform, and then the sensing optical fiber wrapped on its surface is strained. The strain of the sensing optical fiber causes the phase change of the internal reflected light signal. By monitoring and demodulating the phase change of the optical signal, the external acceleration is indirectly measured.

[0014] The uwDAS-based compliant cylindrical fiber optic acceleration sensor test system includes: uwDAS demodulation module, computer, signal generator, power amplifier, vibration table, charge amplifier:

[0015] The output end of the signal generator is connected to the input end of the power amplifier to generate a vibration signal;

[0016] The output end of the power amplifier is connected to the vibration table to drive the vibration table;

[0017] The vibration table is connected to the input of a charge amplifier to amplify the signal.

[0018] The fiber optic acceleration sensor is fixed on the vibration table.

[0019] The computer is connected to the uwDAS demodulation module, and the uwDAS demodulation module is connected to the fiber optic acceleration sensor.

[0020] During the test, the fiber optic accelerometer is firmly adhered to the vibration table to ensure that it is tightly connected to the surface of the vibration table so as to accurately sense the vibration of the vibration table. By adjusting the signal generator, vibration signals of different frequencies are output, and the collected vibration waveforms are recorded on the computer to analyze their frequency response characteristics.

[0021] The present invention provides a compliant cylindrical optical fiber acceleration sensor based on ultra-weak fiber Bragg grating (uwDAS), and the technical effects are as follows:

[0022] 1) The present invention is based on optical fiber sensing technology, is resistant to electromagnetic interference, does not require external power supply, is suitable for inflammable and explosive environments such as coal mines, ensures safety, and avoids the potential safety hazards of electronic acceleration sensors.

[0023] 2) The present invention has universal significance. By changing the mass and shape of the mass block and the elastic body, the frequency response range of the sensor can be adjusted, and it is widely applicable to the fields of earthquake monitoring, structural health monitoring, etc. According to different frequency requirements, the sensor can be designed and optimized in a targeted manner to achieve the best sensitivity and accuracy to meet the requirements of various application scenarios.

[0024] 3) The present invention has a simple structure and low manufacturing cost. It combines fiber Bragg grating technology to achieve large-scale, multi-node distributed vibration monitoring, which is suitable for engineering applications. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 This is the structural diagram of the uwDAS's compliant cylindrical fiber optic acceleration sensor probe.

[0026] Figure 2 This is the sensing principle diagram of uwFBG.

[0027] Figure 3 This is a connection diagram of the uwDAS-based compliant cylindrical fiber optic acceleration sensor test system.

[0028] Figure 4 Schematic diagram of a function signal generator generating a sine wave signal.

[0029] Figure 5 This is the waveform after demodulation of the DAS equipment.

[0030] Figure 6 This is the frequency response curve of the test of the uwDAS-based compliant cylindrical fiber optic accelerometer. DETAILED DESCRIPTION

[0031] like Figure 3 As shown, the present invention provides a compliant cylindrical optical fiber acceleration sensor based on uwDAS, comprising: an elastic body 1, a mass block 2 and a sensing optical fiber 3.

[0032] The uwDAS-based compliant cylindrical optical fiber acceleration sensor is as follows Figure 1 As shown. The sensing optical fiber 3 is tightly wound around the elastic body 1 with a certain prestress, and the two ends of the optical fiber are fixed with UV glue to prevent loosening. The sensing optical fiber 3 is a thin-diameter anti-bending optical fiber engraved with ultra-weak fiber gratings. The diameter of the thin-diameter anti-bending optical fiber is 165um, and ultra-weak fiber gratings 10 with equal spacing L are engraved. The sensing principle is as follows Figure 2 shown.

[0033] Among them, the compliant column type usually refers to a structure with a specific geometric shape and design, where "compliant" means that a certain characteristic (such as cross-section, material, stiffness, etc.) changes continuously in the length direction, and "column type" indicates that the structure is usually in a columnar shape. The compliant column type combines the design concept of continuous change characteristics with columnar geometry, aiming to meet specific application requirements by optimizing structural performance. This design can not only improve the utilization rate of materials, but also improve the overall mechanical properties, making it more adaptable in different application scenarios.

[0034] The laser pulse generator 11 is composed of a narrowband laser (NLL), a semiconductor optical amplifier (SOA) and an erbium-doped fiber amplifier (EDFA). The output optical pulse signal enters the ultra-weak fiber grating (uwFBG) array through the first circulator 12. Part of the optical signal is reflected at each uwFBG, and the remaining optical pulses continue to propagate. The reflected optical signal passes through the second circulator 13 and enters the Faraday rotator 15 for distance compensation; then, the two adjacent uwFBG reflection signals interfere in the 3×3 coupler 14 to generate three signals. These three interference signals are detected by the photodetector 16 and sent to the embedded system 17. The FPGA and ARM architecture in the embedded system 17 are responsible for the A / D conversion, processing and demodulation of the signal. The processed data is transmitted to the computer 6 for display via Ethernet.

[0035] According to the working principle of uwFBG, when the optical fiber between two adjacent uwFBG10 is affected by two adjacent external factors, the pulse light in the optical fiber will undergo a phase change. Through the subsequent demodulation process, the amplitude of the phase change can be quantitatively analyzed to determine the change in the physical quantity acting on the sensing optical fiber. In addition, the interference signal in the 3×3 coupler 14 comes from the reflected light of the two ultra-weak fiber gratings 10, so the demodulated phase change is only related to the sensing fiber segment between the two ultra-weak fiber gratings 10, which means that the optical fiber between each two adjacent uwFBGs can be regarded as an independent sensing unit. This structure enables the sensor to achieve high-sensitivity, multi-point distributed acceleration or vibration monitoring.

[0036] The elastomer 1 is made of polyurethane material with a Young's modulus of about 80 MPa and a Poisson's ratio of about 0.38, an outer radius of 15 mm, an inner radius of 13 mm, and a height of 30 mm.

[0037] The mass block 2 is cast iron with a Young's modulus of about 120 GPa and a Poisson's ratio of 0.3, a radius of 27 mm, a height of 20 mm, and a mass of 0.25 kg.

[0038] The sensing optical fiber 3 is a thin-diameter bend-resistant optical fiber engraved with ultra-weak fiber gratings, with a grating interval of 5m and containing multiple grating points.

[0039] The uwDAS demodulation module 5 is produced by Yichang Ruichuan Optoelectronic Technology Co., Ltd. and has the model number RS-HFBGA-05. The laser emits a light pulse along the optical fiber, which is reflected directionally at the grating position and then interferes after phase compensation. This interference carries the acceleration signal information along the sensing optical fiber 3. The frequency, phase and amplitude information of the signal are extracted by processing the collected data.

[0040] The vibration table 9 is produced by Yangzhou Yingmi Measurement and Control Technology Co., Ltd., and its model is VT series small vibration table. The supporting power amplifier 8 is LA-200 produced by the company, and the charge amplifier 10 is YMC8102A. The signal generator 7 is produced by Nanjing Xinlian Telecommunication Instrument Co., Ltd., and its model is EE1641C.

[0041] uwDAS-based compliant cylindrical fiber optic acceleration sensor test system, such as Figure 3 As shown, it includes a uwDAS demodulation module 5, a computer 6, a signal generator 7, a power amplifier 8, a vibration table 9, and a charge amplifier 10; the output end of the signal generator 7 is connected to the input end of the power amplifier 8, and the signal generator 7 generates a vibration signal with a set frequency and amplitude. Since the output power of the signal generator 7 is small, the power amplifier 8 amplifies the voltage and current of the signal to drive the vibration table 9.

[0042] Next, the output end of the power amplifier 8 is connected to the cable on the lower side of the vibration table 9, and the amplified signal is transmitted to the vibration table 9 through the cable, driving its mechanical movement, so that the vibration table 9 generates periodic vibrations at a set frequency and amplitude.

[0043] Next, the cable on the upper side of the vibration table 9 is connected to the input end of the charge amplifier 10 to collect the vibration signal. During the test, the optical fiber acceleration sensor 4 is placed on the vibration table 9 to ensure that it is firmly in contact with the vibration table 9. By adjusting the signal generator 7 to output vibration signals of different frequencies, the computer system records the phase change of the sensor at the corresponding frequency in real time to analyze its frequency response characteristics.

[0044] Through the above implementation methods, not only can the anti-electromagnetic interference and power supply problems of traditional electronic acceleration sensors be overcome, but high-precision vibration monitoring and acceleration measurement can also be performed in complex environments, which has important engineering application value.

[0045] Embodiment 1, frequency response experiment:

[0046] This experiment used Figure 3 The test system shown in FIG. 1 generates a sinusoidal signal with a frequency range of 4 to 190 Hz through a signal generator 7. Figure 4 As shown. Specifically, the frequency of the signal generator 7 is set as follows: in the range of 4-10Hz, it is gradually increased with a step size of 1Hz; in the range of 10-190Hz, it is gradually increased with a step size of 10Hz, and the amplitude of the signal is set to 2V. The output end of the signal generator 7 is connected to the power amplifier 8 to amplify the power of the signal. The amplified signal is transmitted to the vibration table 9 for generating corresponding mechanical vibrations. The vibration table 9 is connected to the power amplifier 8 and can generate corresponding vibrations according to the input electrical signal.

[0047] The optical fiber acceleration sensor 4 is fixed on the surface of the vibration table 9 and moves synchronously with the vibration table 9, thereby sensing the vibration information of the vibration table 9. The sensing optical fiber 3 structure of the sensor is wound on the polyurethane elastomer. When the vibration table 9 undergoes mechanical vibration, the stress and strain inside the optical fiber change, thereby causing the phase change of the optical signal. By detecting the phase change of the optical signal in the optical fiber, the vibration is detected.

[0048] The signal output by the sensor is amplified by the charge amplifier 10 to ensure the strength and stability of the signal. After the DAS system detects the signal transmitted by the sensor, it demodulates the signal. Figure 5 As shown, the data is transmitted to the computer via the Ethernet interface for recording and analysis.

[0049] During the test, the signal generator 7 gradually increases the frequency of the sinusoidal signal, and the computer system records the phase change of the sensor at the corresponding frequency in real time. Finally, the relationship curve between phase and frequency is obtained, as shown in Figure 6 Analysis Figure 6 It can be seen that at a frequency of 40 Hz, the phase amplitude of the sensor reaches a peak value. This indicates that the sensor has a high sensitivity in this frequency band and can effectively detect low-frequency signals. The experimental results verify the excellent performance of the optical fiber acceleration sensor 4 in low-frequency signal detection, especially in the frequency range of about 40 Hz, which shows good response characteristics, indicating that the optical fiber acceleration sensor 4 has a wide range of application prospects in the low-frequency field.

[0050] The present invention proposes a design of a compliant cylindrical optical fiber acceleration sensor, which combines a mass block with an elastic body to form an effective acceleration detection structure. This design can not only overcome the anti-electromagnetic interference and power supply problems of traditional electronic acceleration sensors, but also perform high-precision vibration monitoring and acceleration measurement in complex environments, and has important engineering application value.

Claims

1. uwDAS-based compliant cylindrical fiber optic acceleration sensor, characterized by include: An elastic body (1), a mass block (2), and a sensing optical fiber (3), wherein the sensing optical fiber (3) is tightly wound around the outer surface of the elastic body (1) and is used to sense the deformation caused by signal excitation, thereby obtaining an acceleration signal, and the mass block (2) is fixed above the elastic body (1), forming an optical fiber acceleration sensor (4).

2. The uwDAS-based compliant cylindrical optical fiber acceleration sensor according to claim 1, characterized in that: The elastic body 1 is a tubular structure with a relatively low Young's modulus. As a sensitive material, it deforms under the stimulation of an external signal, thereby transmitting the external signal change information to the sensing optical fiber (3) wound on its outer surface.

3. The uwDAS-based compliant cylindrical optical fiber acceleration sensor according to claim 1, characterized in that: The mass block (2) is a cylindrical structure with a relatively large mass, and generates displacement under the stimulation of an external signal through its relatively large inertial mass, so as to effectively transmit the external signal to the elastic body (1), thereby causing the elastic body (1) to deform.

4. The uwDAS-based compliant cylindrical optical fiber acceleration sensor according to claim 1, characterized in that: The sensing optical fiber (3) is a thin-diameter anti-bending optical fiber engraved with an ultra-weak fiber grating, and the optical fiber between two adjacent gratings is an independent sensing unit.

5. The uwDAS-based compliant cylindrical optical fiber acceleration sensor according to claim 1, characterized in that: The mass block (2) and the elastic body (1) are fixedly connected via an adhesive.

6. The uwDAS-based compliant cylindrical optical fiber acceleration sensor according to claim 1, characterized in that: The mass of the mass block (2) is greater than the mass of the elastic body (1); when the sensor is stimulated by an external signal, the inertial effect of the mass block (2) can effectively act on the elastic body (1), causing it to deform.

7. The acceleration measurement method of the optical fiber acceleration sensor according to any one of claims 1 to 6, characterized in that: When an external excitation signal acts on the optical fiber acceleration sensor (4), the signal is transmitted to the mass block (2) through the elastic body (1), and the external force causes the mass block (2) to generate acceleration, causing the mass block (2) to be displaced relative to the elastic body (1). The displacement causes the elastic body (1) to deform, thereby causing the sensing optical fiber (3) wound on the surface of the elastic body to be strained; the strain of the sensing optical fiber (3) causes the phase of the reflected light signal inside the sensing optical fiber (3) to change, and the external acceleration is indirectly measured by monitoring and demodulating the phase change of the light signal.

8. A test system for a fiber optic acceleration sensor according to any one of claims 1 to 6, characterized in that: include: uwDAS demodulation module (5), computer (6), signal generator (7), power amplifier (8), vibration table (9), charge amplifier (10): The output end of the signal generator (7) is connected to the input end of the power amplifier (8) to generate a vibration signal; The output end of the power amplifier (8) is connected to the vibration table (9) to drive the vibration table (9); The vibration table (9) is connected to the input end of the charge amplifier (10) to amplify the signal; The optical fiber acceleration sensor (4) is fixed on a vibration table (9); The computer (6) is connected to the uwDAS demodulation module (5), and the uwDAS demodulation module (5) is connected to the optical fiber acceleration sensor (4).

9. The optical fiber acceleration sensor testing method of the testing system according to claim 8, characterized in that: During the test, the optical fiber acceleration sensor (4) is firmly adhered to the vibration table (9) to ensure that it is tightly connected to the surface of the vibration table (9) so as to accurately sense the vibration of the vibration table (9); by adjusting the signal generator (7), vibration signals of different frequencies are output, and the collected vibration waveform is recorded on the computer (6), so as to analyze its frequency response characteristics.

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