Optical fiber distributed three-component sound wave sensing system

Abstract

The invention discloses an optical fiber distributed three-component sound wave sensing system, which belongs to the technical field of optical fiber sensing and comprises a vector sensing optical cable, distributed sound wave demodulation equipment and a three-component decoupling algorithm module. Discrete scattering enhanced optical fibers serve as sensing optical fibers to be wound in all sensing channels, and a sensing unit capable of detecting the amplitude and direction of incident sound waves is formed. Acquiring a time domain signal corresponding to each sensing channel output by the optical time domain reflectometer, and performing window taking operation; and inputting the signal in each time window and the inherent directional sensitivity function of each sensing channel into a three-component decoupling algorithm to restore the three-component acoustic signal. Compared with a traditional optical fiber distributed sound wave sensing system, the direction of sound waves can be measured on the basis of measuring the amplitude of the sound waves, and the system has wide application prospects in the fields of geological exploration, seismic monitoring and the like which have more and more requirements for three-component acoustic data.

Description

Technical Field

[0001] The present invention belongs to the technical field of optical fiber sensing, and more specifically, relates to an optical fiber distributed three-component acoustic wave sensing system. Background Art

[0002] Compared with various traditional electrical sensors, optical fiber sensors have the advantages of high sensitivity, anti-electromagnetic interference, good insulation performance, low cost, small size, light weight, easy installation, and strong environmental adaptability. Therefore, optical fiber sensors are increasingly used in fields such as seismic monitoring, geological resource exploration, perimeter security, and pipeline health monitoring, playing an irreplaceable role. In recent years, due to its characteristics of long detection distance, high spatial resolution, and real-time dynamic measurement compared with point-type sensing and quasi-distributed sensing technologies, optical fiber distributed acoustic sensing (DAS) technology has become a research hotspot. In theory, it can measure the vibration signals of each point on the optical fiber. Currently, most DAS systems are based on phase-sensitive optical time domain reflectometry technology. It utilizes the characteristic that the change in the phase of the backward Rayleigh scattered light in the optical fiber is linearly related to the amplitude of the acoustic wave signal incident on the optical fiber, and can accurately quantitatively demodulate the corresponding acoustic wave signal.

[0003] However, the principle of optical fiber distributed acoustic sensing determines that ordinary straight single-mode optical fibers are only sensitive to acoustic wave signals with axial components, and are insensitive to radially incident acoustic wave signals. A single straight single-mode optical fiber cannot provide three-component vector monitoring data, and cannot more truly and comprehensively reflect the information required by users. With the development of technology, the demand for three-component data in fields such as geological exploration and seismic monitoring is increasing.

[0004] In the existing attempts, Patent CN105116508A proposed a spiral-wound optical cable solution, which can indeed respond to radially incident acoustic waves, but it has no resolution for acoustic waves with the same angle between the incident direction and the winding axis, and cannot separately demodulate the components in each direction, and cannot achieve true three-component demodulation; Patent CN114459376A proposed a sensing solution based on multi-core optical fibers, but currently it can only achieve quasi-static shape perception and cannot achieve dynamic three-component acoustic wave sensing; Patent CN116953612A proposed a method based on a distributed optical fiber sensor array, but it can only achieve sound source localization, cannot accurately measure the acoustic wave amplitude, and also poses significant challenges in multi-source application scenarios.

[0005] Therefore, it is very necessary to design an optical cable with three-component acoustic wave sensing ability. This technology will provide stronger technical support for the fields of geological resource exploration and seismic monitoring, help better penetrate deep into the Earth's interior, and can also provide more accurate earthquake warnings, achieve disaster prevention and mitigation, and realize great social and economic benefits. Summary of the invention

[0006] In view of the defects of the prior art, the purpose of the present invention is to provide a fiber-optic distributed three-component acoustic wave sensing system, aiming to solve the problem that the existing distributed sensing optical cable cannot realize three-component sensing.

[0007] To achieve the above object, the present invention provides a fiber-optic distributed three-component acoustic wave sensing system, comprising a vector sensing optical cable, a distributed acoustic wave demodulation device, and a three-component decoupling algorithm module;

[0008] The vector sensing optical cable comprises periodic vector sensing units connected in sequence, wherein the vector sensing unit comprises N scalar sensing channels and sensitivity enhancement units with different directional sensitivity functions, wherein N is an integer not less than 3, the scalar sensing channel comprises a sensing optical fiber, the sensing optical fiber is wound on the sensitivity enhancement unit, the acoustic wave signal acts on the sensitivity enhancement unit to cause it to deform, and the sensing optical fiber generates corresponding strain, and the strain is loaded on the phase of the optical pulse transmitted in the optical fiber, thereby converting the acoustic wave signal into an optical signal; the directional sensitivity function The incident angle of the sound wave with unit amplitude is When incident on the scalar sensor channel, the amplitude of the time domain signal output by the scalar sensor channel; where θ is the angle between the propagation direction vector of the acoustic wave signal and the z-axis, is the angle between the projection of the acoustic wave signal propagation direction vector on the xOy plane and the x-axis, and j is the serial number of the scalar sensor channel;

[0009] The distributed acoustic wave demodulation device is used to detect the optical signal and demodulate the acoustic wave data of each scalar sensing channel;

[0010] The three-component decoupling algorithm module is used to decouple the acoustic wave data and output a vector acoustic wave signal.

[0011] Furthermore, the three-component decoupling algorithm module includes:

[0012] The directional sensitivity function calibration unit is used to obtain the directional sensitivity functions of N scalar sensor channels. Multiple groups of incident angles are incident on the N scalar sensor channels at the same time. The directional sensitivity values ​​of each scalar sensor channel corresponding to each group of incident angles are regarded as a series of reference points. Sub-reference points are inserted between adjacent reference points to obtain a directional reference sensitivity function with higher angle demodulation resolution.

[0013] A time-domain signal interception unit, which is used to add a time window to the time-domain signals of each scalar sensing channel output by the distributed acoustic wave demodulation device, so as to intercept a segment of time-domain signal to be demodulated. After intercepting the time-domain signal within one time window, the time window is slid to intercept the time-domain signal within the next time window until all time-domain signals are acquired;

[0014] A maximum likelihood matching unit, which is used to calculate the amplitudes of the time-domain signals of N scalar sensing channels within each time window; calculate the likelihood of the above amplitudes and the directional reference sensitivity function, find the reference point corresponding to the maximum likelihood, use the incident angle corresponding to the reference point as the demodulation value of the acoustic wave incident angle, substitute the demodulation value of the acoustic wave incident angle into the directional sensitivity functions of N scalar sensing channels to obtain the directional sensitivity values of N scalar sensing channels, and take the average value to obtain the amplitude of the time-domain signal within each time window;

[0015] A vector decoupling unit, which is used to project the amplitude E demodulated within each time window onto the x, y, and z directions according to the demodulated incident angle to obtain the restored three-component acoustic wave signal e x (t), e y (t), e z (t) within this time window.

[0016] Preferably, the sensitizing unit is a cylinder, the material is TPU, and the Young's modulus is on the order of 100 MPa.

[0017] Preferably, an elliptical groove for placing the sensing optical fiber is provided on the sensitizing unit.

[0018] Preferably, the sensing optical fiber is wound around the sensitizing unit evenly or unevenly;

[0019] When the sensing optical fiber is wound around the sensitizing unit evenly, its shape is defined by the following formula:

[0020]

[0021] where r is the radius of the sensitizing unit, t is a parameter used to write the expressions of x, y, and z, indicating that this structure is a periodically varying structure with t as the parameter, the period is 2π, and α is the optical fiber winding angle;

[0022] When the sensing optical fiber is wound around the sensitizing unit unevenly, the optical fiber winding angle α is a variable that changes with t.

[0023] Preferably, the sensing optical fiber is a periodically discrete backscattering enhanced optical fiber or a single-mode optical fiber; among them, the winding length satisfies:

[0024] If the sensing optical fiber is a periodically discrete backscattering enhanced optical fiber, each scalar sensing channel contains two discrete scattering enhancement points on the sensing optical fiber;

[0025] If the sensing optical fiber is a single-mode optical fiber, the length of the sensing optical fiber in each scalar sensing channel is greater than twice the spatial resolution.

[0026] Preferably, the distributed acoustic wave demodulation device is an optical time domain reflectometer.

[0027] Through the above technical solutions conceived by the present invention, compared with the prior art, the following

[0028] beneficial effects can be achieved:

[0029] 1. The vector sensing optical cable with a special winding structure adopted in the fiber optic distributed three-component acoustic wave sensing system provided by the present invention has different sensitivities to acoustic waves incident in different directions. By jointly solving the responses of multiple sensing channels with different directional sensitivity functions, the direction and amplitude of the acoustic wave can be detected simultaneously;

[0030] 2. The three-component decoupling algorithm module adopted in the fiber optic distributed three-component acoustic wave sensing system provided by the present invention has an interpolation process in the directional sensitivity function calibration unit, which can improve the accuracy as much as possible when the number of calibration points is insufficient, and provides a simple, highly flexible and accurate data demodulation scheme for the vector sensing optical cable proposed in the present invention; the calibration and rematching process in the maximum likelihood matching unit can be adapted to the sensing optical cable with any fiber winding structure, and provides a migratable data demodulation scheme for other optical cables proposed in the future that want to achieve similar functions. Description of the Drawings

[0031] Figure 1 is a schematic diagram of a fiber optic distributed three-component acoustic wave sensing system provided by the present invention;

[0032] Figure 2 is a schematic diagram of a vector sensing unit of a vector sensing optical cable (elliptical winding optical cable) provided by the present invention;

[0033] Figure 3 is a schematic diagram of a periodically discrete backscattering enhanced optical fiber;

[0034] Figure 4 is a flowchart of the three-component decoupling algorithm provided by the present invention;

[0035] Figure 5 is a flowchart of the maximum likelihood matching provided by the present invention. Detailed Embodiments

[0036] In order to make the objectives, technical solutions and advantages of the present invention more clear and understandable, the present invention will be 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. In addition, the technical features involved in the various embodiments of the present invention described below can be combined with each other as long as they do not conflict with each other.

[0037] The present invention provides an optical fiber distributed three-component acoustic wave sensing system, including a vector sensing optical cable, a distributed acoustic wave demodulation device, and a three-component decoupling algorithm module;

[0038] The vector sensing optical cable includes sequentially connected periodic vector sensing units. The vector sensing unit includes N scalar sensing channels with different directional sensitivity functions and a sensitizing unit, where N is an integer not less than 3. The scalar sensing channel includes a sensing optical fiber, and the sensing optical fiber is wound around the sensitizing unit. When an acoustic wave signal acts on the sensitizing unit to cause it to deform, the sensing optical fiber generates a corresponding strain, and this strain is loaded onto the phase of the optical pulse transmitted in the optical fiber, thereby converting the acoustic wave signal into an optical signal; the directional sensitivity function is the amplitude of the time-domain signal output by the scalar sensing channel when an acoustic wave with a unit amplitude is incident on the scalar sensing channel at an incident angle where θ is the angle between the propagation direction vector of the acoustic wave signal and the z-axis, is the angle between the projection of the propagation direction vector of the acoustic wave signal on the xOy plane and the x-axis, and j is the serial number of the scalar sensing channel;

[0039] The distributed acoustic wave demodulation device is used to detect the optical signal and demodulate the acoustic wave data of each scalar sensing channel;

[0040] The three-component decoupling algorithm module is used to decouple the acoustic wave data and output a vector acoustic wave signal.

[0041] Specifically, the three-component decoupling algorithm module includes:

[0042] A directional sensitivity function calibration unit, which is used to obtain the directional sensitivity functions of N scalar sensing channels. By simultaneously incidenting on the N scalar sensing channels with multiple groups of incident angles, regarding the directional sensitivity values of each scalar sensing channel corresponding to each group of incident angles as a series of reference points, and inserting sub-reference points between adjacent reference points, so as to obtain a directional reference sensitivity function with higher angle demodulation resolution

[0043] A time-domain signal truncation unit is used to add a time window to the time-domain signals of each scalar sensing channel output by a distributed acoustic wave demodulation device, respectively, so as to truncate a segment of time-domain signal to be demodulated. After truncating the time-domain signal within one time window, the time window is slid to truncate the time-domain signal within the next time window until all time-domain signals are obtained;

[0044] A maximum likelihood matching unit is used to calculate the amplitudes of the time-domain signals of N scalar sensing channels within each time window; calculate the likelihood of the above amplitudes and the directional reference sensitivity function, find the reference point corresponding to the maximum likelihood, take the incident angle corresponding to the reference point as the demodulation value of the acoustic wave incident angle, substitute the demodulation value of the acoustic wave incident angle into the directional sensitivity functions of N scalar sensing channels, obtain the directional sensitivity values of N scalar sensing channels, and take the average value to obtain the amplitude of the time-domain signal within each time window;

[0045] A vector decoupling unit is used to project the amplitude E demodulated within each time window onto the x, y, and z directions according to the demodulated incident angle to obtain the restored three-component acoustic wave signal e within this time window x (t), e y (t), e z (t).

[0046] As Figure 1 shown is a schematic diagram of an optical fiber distributed three-component acoustic wave sensing system in an embodiment, including a vector sensing optical cable, a distributed acoustic wave demodulation device, and a three-component decoupling algorithm module. Among them, the distributed acoustic wave demodulation device adopts an existing optical fiber distributed acoustic wave sensing system based on technology. During the sensing process, the vector sensing optical cable converts the acoustic signal into an optical signal and inputs it into the distributed acoustic wave demodulation device, and the distributed acoustic wave demodulation device then converts the optical signal into an electrical signal and inputs it into the three-component decoupling algorithm module. The three-component decoupling algorithm module demodulates the electrical signal to restore the three-component acoustic wave information detected by the vector sensing optical cable.

[0047] Hereinafter, the vector sensing optical cable and the three-component decoupling algorithm module proposed by the present invention will be described.

[0048] As Figure 2 shown is a schematic diagram of a vector sensing unit of a vector sensing optical cable in an embodiment, which is composed of a TPU cylinder sensitization unit and three sensing channels with winding angles of α1, α2, and α3 respectively. An elliptical groove for placing the sensing optical fiber is provided on the sensitization unit, and the sensing optical fiber is evenly wound therein to form a sensing channel, and its shape is defined by the following formula:

[0049]

[0050] Among them, r is the radius of the sensitizing unit, t is a parameter used to write the expressions of x, y, and z, indicating that this structure is a structure that changes periodically with t as the parameter, with a period of 2π, and α i (i = 1, 2, 3) is the fiber winding angle.

[0051] The directional sensitivity functions of these three sensing channels are respectively respectively represent the amplitude of the time-domain signal output by the scalar sensing channel when a sound wave with a unit amplitude is incident at an incident angle onto the scalar sensing channel; where θ is the angle between the sound wave signal propagation direction vector and the z-axis, and is the angle between the projection of the sound wave signal propagation direction vector on the xOy plane and the x-axis. Figure 3 FIG. shows a schematic diagram of a periodically discrete backscattering enhanced optical fiber adopted in an embodiment, which can be obtained by continuously ultraviolet exposing an ordinary single-mode optical fiber. Compared with an ordinary single-mode optical fiber, it has higher stability and signal-to-noise ratio, and can effectively improve the sensing accuracy. Each sensing channel contains discrete scattering enhancement points on two sensing optical fibers.

[0052] Such as Figure 4 shown is a flow chart of a three-component decoupling algorithm in an embodiment, which mainly includes steps S1 to S4. Hereinafter, each step will be described.

[0053] Step S1: After manufacturing a vector sensing unit, a series of sound waves with different incident angles are emitted to it in the laboratory, and the incident angle is denoted as The time-domain response waveforms of the three sensing channels are respectively recorded, and their amplitudes are fitted. Subsequently, two-dimensional interpolation is performed on and then the above amplitudes are also interpolated accordingly, so as to obtain the directional reference sensitivity function

[0054] of each sensing channel as the reference point for subsequent demodulation.

[0055] Among them, the frequency of the sound wave is a fixed value, and the sound pressure amplitude is fixed at 1 Pa.

[0056] Step S2: During a certain sensing process, a time window is respectively added to the time-domain waveforms corresponding to the three sensing channels output by the distributed acoustic wave demodulation device, and a section of the time-domain signal near a certain moment we hope to demodulate is intercepted.

[0057] If we also want to demodulate the acoustic wave information at other moments, the time window can be slid to intercept a section of the signal near the corresponding moment. c where the length of the window is represented by the number of time points, and the length of the window is T + 1, that is, if the start moment of the window is t0 and the time sampling frequency of the system is f Calculate the amplitude and direction of the sound wave based on the data within this time period.

[0058] Step S3: As Figure 5 shown is the maximum likelihood matching adopted in an embodiment, that is, the flowchart of step S3, which includes the following sub-steps:

[0059] Step S31: Using the time-domain waveform intercepted in S2, calculate the response amplitudes of the three sensing channels within this time window, denoted as A1, A2, and A3.

[0060] Step S32: Calculate the likelihood between (A1, A2, A3) and each reference point intervals.

[0061] Step S33: Find the maximum value among the above likelihoods to achieve maximum likelihood matching, and use the angle value represented by the corresponding reference point as the demodulation value of the sound wave incident angle.

[0062] Step S34: Since the response of each sensing channel is linear, the sensitivity of the three sensing channels at the angle can be used to calculate the sound wave amplitude respectively, and the average value is taken to reduce the error, obtaining the demodulated sound wave amplitude E.

[0063] Step S4: Project the sound wave amplitude E demodulated in S34 onto the x, y, and z directions according to the demodulated incident angle to obtain the restored three-component sound wave signal e x (t), e y (t), e z (t).

[0064] If you want to demodulate the signals at other times, you can slide the time window and repeat steps S3 and S4 to obtain the corresponding three-component sound wave signals.

[0065] Those skilled in the art can easily understand that the above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent replacements, and improvements made within the spirit and principle of the present invention should be included in the protection scope of the present invention.

Claims

1. An optical fiber distributed three-component acoustic wave sensing system, characterized in that: It includes vector sensing optical cable, distributed acoustic wave demodulation equipment and three-component decoupling algorithm module; The vector sensing optical cable comprises periodic vector sensing units connected in sequence, wherein the vector sensing unit comprises N scalar sensing channels and a sensitivity enhancement unit with different directional sensitivity functions, wherein N is an integer not less than 3, the scalar sensing channel comprises a sensing optical fiber, the sensing optical fiber is wound on the sensitivity enhancement unit, and the periodic vector sensing unit is used to convert an acoustic wave signal into an optical signal; the directional sensitivity function The incident angle of the sound wave with unit amplitude is The amplitude of the time domain signal output by the scalar sensor channel when incident on the scalar sensor channel; where θ is the angle between the propagation direction vector of the acoustic wave signal and the z-axis, is the angle between the projection of the acoustic wave signal propagation direction vector on the xOy plane and the x-axis, and j is the serial number of the scalar sensor channel; The distributed acoustic wave demodulation device is used to detect the optical signal and demodulate the acoustic wave data of each scalar sensing channel, wherein the acoustic wave data is a time domain signal; The three-component decoupling algorithm module is used to decouple the acoustic wave data and output a vector acoustic wave signal.

2. The optical fiber distributed three-component acoustic wave sensing system according to claim 1, characterized in that: The sensitizing unit is a cylinder, made of TPU, and has a Young's modulus of the order of 100 MPa.

3. The optical fiber distributed three-component acoustic wave sensing system according to claim 2, characterized in that: The sensitivity enhancement unit is provided with an elliptical groove for placing the sensing optical fiber.

4. The optical fiber distributed three-component acoustic wave sensing system according to claim 3, characterized in that: The sensing optical fiber is evenly wound on the sensitivity enhancement unit or unevenly wound on the sensitivity enhancement unit; When the sensing fiber is evenly wound around the sensitivity enhancement unit, its shape is defined by the following formula: Among them, r is the radius of the sensitivity enhancement unit, t is a parameter used to write the expression of x, y, and z, indicating that the structure is a structure that changes periodically with t as a parameter, with a period of 2π, and α is the fiber winding angle; When the sensing optical fiber is unevenly wound on the sensitivity enhancement unit, the optical fiber winding angle α is a variable that changes with t.

5. The optical fiber distributed three-component acoustic wave sensing system according to claim 3, characterized in that: The sensing optical fiber is a periodic discrete backscattering enhanced optical fiber or a single-mode optical fiber; wherein the winding length satisfies: If the sensing optical fiber is a periodic discrete backscattering enhanced optical fiber, each scalar sensing channel contains two discrete scattering enhancement points on the sensing optical fiber; If the sensing optical fiber is a single-mode optical fiber, the length of the sensing optical fiber in each scalar sensing channel is greater than twice the spatial resolution.

6. The optical fiber distributed three-component acoustic wave sensing system according to claim 1, characterized in that: The three-component decoupling algorithm module includes: The directional sensitivity function calibration unit is used to obtain the directional sensitivity functions of N scalar sensor channels. The acoustic wave signals are incident on the N scalar sensor channels at multiple incident angles at the same time. The directional sensitivity values ​​of each scalar sensor channel corresponding to each incident angle are regarded as a series of reference points. Sub-reference points are inserted between adjacent reference points to obtain a directional reference sensitivity function with higher angle demodulation resolution. The time domain signal interception unit is used to add a time window to the time domain signal of each scalar sensor channel output by the distributed acoustic wave demodulation device to intercept a section of the time domain signal to be demodulated. After intercepting the time domain signal in a time window, the time window is slid to intercept the time domain signal in the next time window until all the time domain signals are acquired; The maximum likelihood matching unit is used to calculate the amplitude of the time domain signal of N scalar sensor channels in each time window; calculate the above amplitude and , find the reference point corresponding to the maximum likelihood, use the incident angle corresponding to the reference point as the acoustic incident angle demodulation value, bring the acoustic incident angle demodulation value into the directional sensitivity function of the N scalar sensor channels, obtain the directional sensitivity values ​​of the N scalar sensor channels, take the average value, and obtain the amplitude of the time domain signal in each time window; The vector decoupling unit is used to project the demodulated amplitude E in each time window to the three directions of x, y, and z according to the demodulated incident angle to obtain the restored three-component sound wave signal e in the time window. x (t), e y (t), e z (t).

7. The optical fiber distributed three-component acoustic wave sensing system according to claim 1, characterized in that: The distributed acoustic wave demodulation device is an optical time domain reflectometer.

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