UwDAS-based secondary sensitivity optical fiber microphone

Abstract

The secondary sensitization type optical fiber microphone based on uwDAS comprises a core shaft, a shell and a sensing optical fiber; the sensing optical fiber is tightly wound in the middle of the core shaft to form a first sensitization type optical fiber microphone assembly; the core shaft is fixed in the shell to form a second sensitization type optical fiber microphone. The optical fiber microphone is fixed on the bottom center of the shell by the optical fiber microphone assembly. The optical fiber microphone is made of the optical fiber engraved with uwFBG. Since a single optical fiber can multiplex multiple gratings and the sensing optical fiber between two adjacent uwFBGs is regarded as an independent sensing unit, multiple independent optical fiber microphones can be constructed on one optical fiber to realize the multi-node sound wave signal acquisition. The optical fiber microphone can realize the high-sensitivity and high-precision detection of the sound wave signal.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of acoustic sensing, in particular to a secondary sensitization type optical fiber microphone based on uwDAS. BACKGROUND

[0002] The Distributed Acoustic Sensing (DAS) system based on Ultra weak Fiber Bragg Grating (uwFBG) (uwDAS) uses the Fizeau interference principle to sense the phase change caused by the acoustic wave, and then restores the acoustic wave information, has the characteristics of passive, anti-electromagnetic interference, large capacity, etc., and the number of multiplexed gratings in a single optical fiber can reach tens of thousands, which can realize distributed data acquisition of multiple nodes, and is widely used in pipeline leakage monitoring, sound source identification, machine fault diagnosis and other fields.

[0003] Under the action of sound waves, the optical fiber deforms and causes changes in the phase in the optical fiber, but due to the high Young's modulus of the optical fiber, the sensitivity of the optical fiber to direct detection of sound waves is low, which greatly limits its application in some fields. Therefore, sensitization is a key step to improve the detection performance and accuracy, and the sensing optical fiber is usually wound on a sensitization structure to improve the response ability of the optical fiber to sound waves, and the sensitization structure can be reasonably designed according to the detection object, which makes the application of the optical fiber microphone have high customizability and flexibility.

[0004] In practical applications, such as fault detection of belt conveyors, multi-point monitoring using optical fiber microphones can comprehensively obtain sound wave signals during belt conveyor operation, and potential problems such as abnormal friction, bearing failure, and belt tearing can be found in time by analyzing the changes in the sound wave signals, which can significantly improve the efficiency of fault diagnosis and maintenance. The sensing optical fiber of the common optical fiber microphone is usually exposed to the outside, which is easily affected by mechanical damage and environmental pollutants such as dust, which may cause performance degradation or failure. SUMMARY

[0005] To solve the above technical problems, the present application provides a secondary sensitization type optical fiber microphone based on uwDAS, which can realize high sensitivity and high precision detection of sound wave signals.

[0006] The technical scheme adopted by the present application is:

[0007] The secondary sensitization type optical fiber microphone based on uwDAS comprises a mandrel, a shell and a sensing optical fiber.

[0008] The sensing optical fiber is tightly wound in the middle of the mandrel to form a first sensitization type optical fiber microphone assembly.

[0009] The mandrel is fixed in the shell, and constitutes a second time-sensitized fiber microphone.

[0010] The fiber microphone is fixed by a fiber microphone assembly at the center of the bottom of the shell.

[0011] The mandrel is a hollow cylinder with a low Young's modulus, and serves as a sound-sensitive material to generate deformation under the action of sound waves.

[0012] One fiber can multiplex multiple uwFBGs, and the fiber between two adjacent uwFBGs is an independent sensing unit, so that multiple fiber microphones can be constructed on one fiber to form a fiber microphone array, and different fiber microphones in the fiber microphone array can simultaneously detect different sound signals with high sensitivity to realize multi-node sound signal acquisition.

[0013] The sensing fiber is tightly wound in the middle of the mandrel with a certain pre-tension to constitute a fiber microphone assembly of the mandrel structure, and realize the first time-sensitization.

[0014] The shell has the same height as the length of the mandrel, and includes a shell cover and a shell body, and a pickup hole and a fiber leading hole are formed in the side surface of the shell body, and the fiber leading hole is used to lead the sensing fiber.

[0015] The sound signal detection method of the uwDAS-based second time-sensitized fiber microphone, wherein sound waves directly act on the mandrel through the pickup hole, and then act on the mandrel after being reflected by the shell, so that the mandrel is deformed to drive the axial length of the sensing fiber to change, causing the phase change of the light pulse in the fiber, and thus the detection of the sound signal is realized.

[0016] The manufacturing method of the uwDAS-based second time-sensitized fiber microphone, which is manufactured based on the uwFBG-marked fiber, and multiple fiber microphones are constructed on one fiber to form a fiber microphone array, and different fiber microphones in the fiber microphone array can simultaneously detect different sound signals with high sensitivity to realize multi-node sound signal acquisition.

[0017] The test system of the uwDAS-based second time-sensitized fiber microphone, which includes a uwDAS demodulation module, a computer, an audio signal generator, a sound pressure meter, and a bare fiber ring; the fiber microphone assembly and the bare fiber ring used for comparison are different grid points on one fiber, i.e., two independent sensing units; during the test, the object to be tested is placed on a flat shock-absorbing sponge and then put into an acoustic box to reduce the interference of external vibration and echo; the fiber microphone assembly is connected with the uwDAS demodulation module, the uwDAS demodulation module is connected with the computer, and the computer is used to display the test signal in real time; the computer drives the audio signal generator to generate the required sound wave signal, and makes the sound wave incident along the radial direction of the fiber microphone assembly; the sound pressure meter is placed in a place with the same sound pressure as the fiber microphone assembly, and is used for sound pressure sensitivity calibration test.

[0018] The technical effects of the application are as follows:

[0019] 1) The optical fiber microphone of the application adopts a core shaft plus shell sensitization structure, and the sensing optical fiber is tightly wound on the core shaft. Due to the low Young's modulus of the core shaft material, the core shaft produces large deformation under the action of sound waves, thereby driving the optical fiber to deform and realize the first sensitization. In addition, the effective reflection of the shell to the sound waves enhances the sound wave signal received by the core shaft to a certain extent, further improves the sound pressure sensitivity of the optical fiber microphone, and realizes the second sensitization.

[0020] 2) The shell of the optical fiber microphone not only contributes to the sound pressure sensitivity of the optical fiber microphone, but also provides a solid physical barrier for the internal core shaft structure, avoiding mechanical damage and environmental pollutants such as dust during actual work, ensuring the stability of the performance of the optical fiber microphone, and facilitating fixation and installation, suitable for various environments.

[0021] 3) Compared with the single core shaft structure, the core shaft plus shell structure proposed by the application improves the resonant frequency of the optical fiber microphone structure to a certain extent due to the constraint effect of the shell on the core shaft, and expands the working bandwidth of the optical fiber microphone.

[0022] 4) The application is based on the optical fiber engraved with uwFBG. Since a single optical fiber can multiplex multiple gratings and the sensing optical fiber between two adjacent uwFBGs is regarded as an independent sensing unit, multiple independent optical fiber microphones can be constructed on one optical fiber to realize multi-node sound wave signal acquisition.

[0023] 5) The structure of the application has universal significance and is suitable for sound wave detection and analysis in various scenes, such as fault detection of belt conveyors, detection and recognition of human voice signals, etc. According to different test requirements such as sensitivity, working bandwidth, etc., based on the core shaft plus shell structure proposed by the application, the principle of low Young's modulus of the core shaft material and the supporting effect of the shell and the effective reflection of the shell to the sound waves, the material, size, etc. Parameters of the core shaft and the shell can be appropriately changed, and the application has a wide range of application scenarios.

[0024] 6) The optical fiber microphone based on the uwDAS secondary sensitization structure design of the application has high sensitivity, high signal-to-noise ratio, high fidelity, good linearity, repeatability and hysteresis, etc. BRIEF DESCRIPTION OF DRAWINGS

[0025] Figure 1 is the structure diagram of the first sensitized optical fiber microphone assembly.

[0026] Figure 2 is the structure of the second sensitized optical fiber microphone Figure 1 ;

[0027] Figure 3 Fiber microphone structure for second sensitization Figure 2 .

[0028] Figure 4 Sensing principle diagram for uwFBG.

[0029] Figure 5 Multi-node sound wave signal collection schematic diagram for fiber microphone based on uwFBG.

[0030] Figure 6 Connection schematic diagram of fiber microphone test system in Example 1.

[0031] Figure 7 Frequency response curve in Example 1.

[0032] Figure 8 Resonant mode diagram of mandrel structure in Example 1.

[0033] Figure 9 Curve of fiber phase change with sound pressure of mandrel structure in Example 2.

[0034] Figure 10 Curve of fiber phase change with sound pressure of mandrel plus shell structure in Example 2.

[0035] Figure 11 Frequency spectrum diagram of bare fiber ring at 1000 Hz in Example 3.

[0036] Figure 12 Frequency spectrum diagram of mandrel structure at 1000 Hz in Example 3.

[0037] Figure 13 Frequency spectrum diagram of mandrel plus shell structure at 1000 Hz in Example 3.

[0038] Figure 14 Time-frequency diagram of original normal sound of belt conveyor in Example 4.

[0039] Figure 15 Time-frequency diagram of normal sound detected by mandrel structure in Example 4.

[0040] Figure 16 Time-frequency diagram of normal sound detected by mandrel plus shell structure in Example 4.

[0041] Figure 17 Time-frequency diagram of original fault sound of belt conveyor in Example 4.

[0042] Figure 18 Time-frequency diagram of fault sound detected by mandrel structure in Example 4.

[0043] Figure 19A time-frequency map of the fault sound for the mandrel plus shell structure detection in Example 4. DETAILED DESCRIPTION

[0044] As shown in Figure 3 , the application provides a secondary sensitization structure design of a fiber microphone based on uwDAS, which comprises a mandrel 1, a shell 2 and a sensing fiber 3.

[0045] The fiber microphone assembly 5 of the first sensitized mandrel structure is as shown in Figure 1 . A fine-diameter anti-bending sensing fiber with a grating spacing of 5m is tightly wound in the middle of the mandrel 1 with a certain pre-stress, and the ends of the fiber are fixed with adhesive tape to prevent loosening. The fine-diameter anti-bending fiber has a diameter of 165um, and the engraved ultra-weak fiber grating (uwFBG) 17 sensing principle is as shown in Figure 4 . A laser pulse generator 18 composed of a narrowband laser (NLL), a semiconductor optical amplifier (SOA) and an erbium-doped fiber amplifier (EDFA) outputs an optical pulse signal, which is coupled into the uwFBG 17 in sequence through a first circulator 19 and reflects a small part of the optical signal, and the remaining optical pulse continues to transmit backward. The reflected light signal is output from the first circulator 19, passes through a second circulator 20, is coupled into a Faraday rotator mirror 22 with an arm length difference of the adjacent uwFBG spacing (5m) for distance compensation, so that the reflected light signals of the adjacent two uwFBGs 17 interfere in the 3×3 coupler 21, and the signals are output in three paths and received by a photodetector 23. The collected signals are demodulated and calculated by an embedded circuit 24, and the processing results are displayed on a computer 11. According to the sensing principle of the uwFBG, when the fiber between the two adjacent uwFBGs 17 is subjected to external sound waves, stress, etc., the phase change of the pulse light in the fiber will be caused, and the size of the phase change can be quantitatively analyzed through subsequent demodulation processing, so as to determine the change of the physical quantity acting on the sensing fiber. Moreover, the interference in the 3×3 coupler 21 is the reflected light signals of the adjacent two uwFBGs 17, and the size of the phase change demodulated only relates to the sensing fiber between the two uwFBGs 17, that is, the fiber between the adjacent two uwFBGs can be regarded as an independent sensing unit.

[0046] The mandrel is a foam material with a Young's modulus of about 16.5MPa and a Poisson's ratio of about 0.35, and has an outer radius of 2.7cm, a thickness of 0.7cm and a length of 5.2cm.

[0047] As shown in Figure 2As shown, the shell 2 structure is a cylindrical aluminum shell, including shell cover 6 and shell body 7, aluminum shell radius is 4 cm, height is 5.2 cm, shell body 7 side 8 small holes as a pickup hole 8; At the same time set up a fiber exit hole 9. Pickup hole 8 diameter is about 3 mm, for two rows, each row of 4, left and right spacing is about 1.5 cm, the spacing is about 1 cm. Fiber exit hole 9 diameter is about 2 mm, for leading out sensing optical fiber 3, convenient to connect with uwDAS demodulation equipment 10.

[0048] The uwDAS demodulation equipment 10 is produced by Yichang Rui Chuan Optoelectronic Technology Co., Ltd., model is RS-HFBGA-05, laser along the optical fiber emits light pulse, directional reflection at the grating position, after phase compensation interference, this interference carries the vibration information along the line of sensing optical fiber 3, through processing the collected data to extract the frequency, phase and amplitude information of the signal.

[0049] The second time of the core shaft plus shell structure of the fiber microphone 4 is as shown in Figure 3 The core shaft structure of the fiber microphone assembly 5 as shown in Figure 1 The core shaft structure of the fiber microphone assembly 5 is fixed with adhesive tape on the bottom of the aluminum shell, and the sensing optical fiber 3 is led out from the fiber exit hole 9.

[0050] Since a fiber can reuse multiple uwFBG, and the fiber between the adjacent two uwFBG can be regarded as an independent sensing unit, then multiple fiber microphones 4 can be constructed on a fiber to form a fiber microphone array 25, as shown in Figure 5 Different fiber microphones 4 in the array can simultaneously detect different acoustic signals with high sensitivity, realizing multi-node acoustic signal acquisition.

[0051] The test system of the fiber microphone 4 is as shown in Figure 6As shown, including uwDAS demodulation module 10, computer 11, audio signal generator 12, sound pressure meter 13, bare fiber ring 14, optical fiber microphone 4. Among them, the optical fiber microphone assembly 5 with mandrel structure can be tested after removing the shell 2 of the optical fiber microphone 4 with shell structure, and the optical fiber microphone 4 / optical fiber microphone assembly 5 and the bare fiber ring 14 for comparison are different grid points on a fiber, that is, two independent sensing units. During testing, the object to be tested is placed on a flat shock-absorbing sponge 15 and placed in an acoustic box 16 together to reduce external vibration and echo interference. The optical fiber microphone 4 / optical fiber microphone assembly 5 is connected with the uwDAS demodulation module 10, and the uwDAS demodulation module 10 is connected with the computer 11 to display the test signal in real time. The computer 11 drives the audio signal generator 12 to generate the required sound wave signal, and makes the sound wave incident along the optical fiber microphone 4 / optical fiber microphone assembly 5 radially, and the sound pressure meter 13 is placed in the same sound pressure as the optical fiber microphone 4 / optical fiber microphone assembly 5, for sound pressure sensitivity calibration test.

[0052] Through the above embodiment, by tightly winding the sensing optical fiber 3 on the mandrel 1 and fixing it in the shell 2, the secondary sensitization structure design of the optical fiber microphone is realized, and the important performance such as sound pressure sensitivity is greatly improved, which has important application value in the field of sound wave monitoring.

[0053] Example 1, frequency response experiment:

[0054] According to the test system shown in Figure 6 , the audio generator generates a sine signal in the frequency range of 50-2000Hz, with a step of 50Hz, and records the phase information obtained by the computer at each frequency and the corresponding sound pressure meter 13 value. The ratio of phase to sound pressure is the sound pressure sensitivity of the optical fiber microphone 4 at that frequency. The sound pressure sensitivity curves of the bare fiber ring 14, the mandrel structure and the mandrel plus shell structure with frequency are tested respectively, and the frequency response curves are obtained, as shown in Figure 7 . As shown in Figure 7 , the average sound pressure sensitivity of the bare fiber ring, the mandrel structure and the mandrel plus shell structure in the frequency range of 50-2000Hz is-137.6dB re 1rad / uPa, -122.3dB re 1rad / uPa, -116.0dB re 1rad / uPa respectively, and the mandrel plus shell structure optical fiber microphone has the largest average sound pressure sensitivity. The mandrel structure has a resonance peak around 1450Hz, and the characteristic frequency analysis of the structure shows that the resonance frequency is 1431.1Hz, as shown in Figure 8 , the simulation and experiment are basically consistent. The mandrel plus shell structure proposed in the application does not have a resonance peak in this frequency range, and the working bandwidth of the optical fiber microphone is expanded.

[0055] Example 2, linearity, repeatability and latency experiment:

[0056] According to the test system shown in Figure 6 , the frequency of the sine sound wave output by the audio signal generator 12 is fixed at 100 Hz, the sound pressure is changed from small to large and then from large to small, and this is repeated twice, the phase information obtained by the computer host under each sound pressure signal and the corresponding sound pressure meter value are recorded, the scatter plot of the phase change with the sound pressure is drawn, and linear fitting is performed on each group of scatter plots. The mandrel structure and the mandrel plus shell structure are tested respectively, and the results are shown in Figure 9 , Figure 10 .

[0057] The test results of Figure 9 , Figure 10 are analyzed, and the linearity is shown in Table 1, the repeatability is shown in Table 2, and the latency is shown in Table 3.

[0058] Table 1 Linearity of test results

[0059]

[0060] Table 2 Repeatability of test results

[0061]

[0062] Table 3 Latency of test results

[0063]

[0064] From the analysis results of Tables 1-3, the linearity, repeatability and latency of the mandrel and the mandrel plus shell structure are good, among which the linearity and repeatability of the mandrel plus shell structure are better than those of the mandrel structure, and the latency of the mandrel structure is better than that of the mandrel plus shell structure. Overall, the optical fiber microphone 4 with the mandrel plus shell structure proposed in the present application has excellent performance in linearity, repeatability and latency.

[0065] Example 3, signal-to-noise ratio experiment:

[0066] According to the test system shown in Figure 6 , the audio generator outputs a 1000 Hz sine sound wave signal, and the frequency spectrum analysis is performed on the signals detected by the bare fiber ring, the mandrel structure and the mandrel plus shell structure, and the results are shown in Figure 11 , Figure 12 , Figure 13 . From Figure 11 , Figure 12 , Figure 13It can be known that the signal-to-noise ratio of the bare fiber ring of the two structures of the mandrel and the mandrel plus shell is greatly improved, and the signal-to-noise ratio of the optical fiber microphone with the mandrel plus shell structure is the largest, which is about 25dB higher than that of the bare fiber ring.

[0067] Example 4, fidelity experiment:

[0068] According to the test system shown in Figure 6 A group of Harvard voices were selected for fidelity testing. The computer's Google Translate was used to read the text and connect the audio generator to output the voice signal, and the voice signal detected by the probe was converted into a WAV file, which was recognized by the Feishu Miaojue voice recognition software. The voice used for testing was 10 sentences and 80 words, and the original text was:

[0069] 1)The birch canoe slid on the smooth planks.

[0070] 2)Glue the sheet to the dark blue background.

[0071] 3)It's easy to tell the depth of a well.

[0072] 4)These days a chicken leg is a rare dish.

[0073] 5)Rice is often served in round bowls.

[0074] 6)The juice of lemons makes fine punch.

[0075] 7)The box was thrown beside the parked truck.

[0076] 8)The hogs were fed chopped corn and garbage.

[0077] 9)Four hours of steady work faced us.

[0078] 10)Alarge size in stockings is hard to sell.

[0079] The recognition results are as follows, add the bottom line is the word of the recognition error, the mandrel structure of the fiber microphone consensus recognition wrong 6 words.

[0080] 1)The birch canoe slid on smooth

[0081] 2)Glue the sheet to the dark blue background.

[0082] 3)It's easy to tell the of a well.

[0083] 4)These days a chicken leg is a rare dish.

[0084] 5)Rice is often served in round bowls.

[0085] 6)The juice of lemons makes fine punch.

[0086] 7)The box was thrown beside the truck.

[0087] 8)The hogs were fed chopped corn and garbage.

[0088] 9)Four hours of steady work .

[0089] 10)Alarge size in stockings is hard to sell.

[0090] The mandrel plus shell structure of the fiber microphone consensus recognition wrong 3 words.

[0091] 1)The birch canoe slid on the smooth .

[0092] 2)glue the sheet to the dark blue background.

[0093] 3)It's easy to tell the depth of a well.

[0094] 4)These days a chicken leg is a dish.

[0095] 5)Rice is often served in round .

[0096] 6)The juice of lemons makes fine punch.

[0097] 7)The box was thrown beside the parked truck.

[0098] 8)The hogs were fed chopped corn and garbage.

[0099] 9)Four hours of steady work faced us.

[0100] 10)A large size in stockings is hard to sell.

[0101] According to the test results, both structures can accurately identify most of the words, and the fidelity of the core shaft plus shell structure proposed in the application is higher than that of the core shaft structure.

[0102] Example 5, belt conveyor data experiment:

[0103] According to the test system shown in Figure 6 , the audio generator plays the collected belt conveyor audio file, and the data detected by the optical fiber microphone of the original audio and the core shaft structure and the core shaft plus shell structure are compared in time-frequency domain. The time-frequency diagram of the original normal sound is shown in Figure 14 , the audio generator plays the normal sound data of the belt conveyor, and the time-frequency diagrams of the detection results of the core shaft structure and the core shaft plus shell structure are shown in Figure 15 , Figure 16 .

[0104] As can be seen from Figure 14 , the frequency range of the normal sound of the belt conveyor is concentrated below 500Hz, and from Figure 15 , Figure 16The frequency domain graph of the original data shows that the mandrel structure and the mandrel plus shell structure can detect normal sound below 500Hz well, but the mandrel structure has certain frequency components in the frequency range of 2000-2500Hz, and the optical fiber microphone with the mandrel plus shell structure does not have this phenomenon, and is more consistent with the original data.

[0105] The time-frequency graph of the original fault sound is shown in Figure 17 The time-frequency graph of the detection results of the mandrel structure and the mandrel plus shell structure is shown in Figure 18 、 Figure 19 .

[0106] As can be seen from Figure 17 , the frequency range of the belt machine fault sound is concentrated in 500-1000Hz, and the frequency domain graph of Figure 18 、 Figure 19 shows that the mandrel structure and the mandrel plus shell structure can detect the fault sound concentrated in 500-1000Hz well. Like the normal data of the belt machine, the result of the mandrel structure has more frequency components at frequencies higher than the fault sound, and the optical fiber microphone with the mandrel plus shell structure proposed by the application is more consistent with the original data. Therefore, whether it is to detect the normal sound or the fault sound of the belt machine, the optical fiber microphone with the mandrel plus shell structure proposed by the application is more feasible.

Claims

1. A secondary-sensitivity-enhanced fiber optic microphone based on uwDAS, characterized in that... include: The components are: a spindle (1), a housing (2), and a sensing fiber (3); the sensing fiber (3) is tightly wound around the spindle (1) to form a fiber optic microphone assembly (5) with the first enhancement of sensitivity; the spindle (1) is fixed inside the housing (2) to form a fiber optic microphone (4) with the second enhancement of sensitivity. The fiber optic microphone (4) is formed by fixing the fiber optic microphone assembly (5) to the center of the bottom of the housing (2); The outer shell (2) is a cylindrical aluminum shell. The height of the outer shell (2) is the same as the length of the spindle (1). The outer shell (2) includes a shell cover (6) and a shell body (7). A pickup hole (8) and an optical fiber outlet hole (9) are opened on the side of the shell body (7). The optical fiber outlet hole (9) is used to lead out the sensing optical fiber (3).

2. The secondary-sensitivity-enhanced fiber optic microphone based on uwDAS according to claim 1, characterized in that: The mandrel (1) is a hollow cylinder with a low Young's modulus, which deforms under the action of sound waves as a sound-sensitive material.

3. The secondary-sensitivity-enhanced fiber optic microphone based on uwDAS according to claim 1, characterized in that: A single optical fiber can reuse multiple uwFBGs, and the optical fiber between two adjacent uwFBGs is an independent sensing unit. Thus, multiple optical fiber microphones (4) can be constructed on a single optical fiber to form an optical fiber microphone array (25). Different optical fiber microphones (4) in the optical fiber microphone array (25) can simultaneously perform high-sensitivity detection on different acoustic signals, thereby realizing the acquisition of acoustic signals from multiple nodes.

4. The secondary-sensitivity-enhancing fiber optic microphone based on uwDAS according to claim 1, characterized in that: The sensing fiber (3) is tightly wound around the core shaft (1) with a certain prestress to form a fiber optic microphone assembly (5) with a core shaft structure, thereby achieving the first enhancement of sensitivity.

5. The sound signal detection method of a secondary-sensitivity-enhanced fiber optic microphone based on uwDAS as described in any one of claims 1 to 4, characterized in that: The sound wave passes through the pickup hole (8) and acts directly on the spindle (1). After being reflected by the outer shell (2), it acts on the spindle (1), causing the spindle (1) to deform and thus causing the axial length of the sensing fiber (3) to change, causing the phase change of the optical pulse in the fiber, thereby realizing the detection of the sound signal.

6. The method for manufacturing a secondary-sensitivity-enhanced fiber optic microphone based on uwDAS as described in any one of claims 1 to 4, characterized in that: Based on optical fibers engraved with uwFBG, multiple optical fiber microphones (4) are constructed on a single optical fiber to form an optical fiber microphone array (25). Different optical fiber microphones (4) in the optical fiber microphone array (25) can simultaneously perform high-sensitivity detection of different sound wave signals, thereby realizing the acquisition of sound wave signals from multiple nodes.

7. The test system for a secondary-sensitivity-enhancing fiber optic microphone based on uwDAS as described in any one of claims 1 to 4, characterized in that: Includes uwDAS demodulation module (10), computer (11), audio signal generator (12), sound pressure meter (13), bare fiber ring (15); The fiber optic microphone assembly (5) and the bare fiber ring (14) used for comparison are different gratings on the same fiber, which are two independent sensing units; During testing, the object to be tested is placed on a flat damping sponge (15) and put into a sound-absorbing box (16) together to reduce the interference of external vibration and echo. Connect the fiber optic microphone assembly (5) to the uwDAS demodulation module (10), and connect the uwDAS demodulation module (10) to the computer (11) for real-time display of test signals; the computer (11) drives the audio signal generator (12) to generate the required sound wave signal and make the sound wave incident radially along the fiber optic microphone assembly (5); the sound pressure meter (13) is placed at the same sound pressure level as the fiber optic microphone assembly (5) for sound pressure sensitivity calibration test.

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