Optical fiber photoacoustic gas sensing system and method for inhibiting environmental noise interference

Abstract

The invention belongs to the technical field of photoacoustic spectrum gas sensing, and discloses an optical fiber photoacoustic gas sensing system and method for inhibiting environmental noise interference. The system comprises a narrow linewidth laser, a double-core optical fiber, a symmetrical optical fiber photoacoustic sensing probe, a wide-spectrum detection light source, an optical circulator, a spectrograph and a control circuit. The air cavities on the two sides of the symmetrical optical fiber photoacoustic sensing probe are consistent in structure and opposite in direction, and the vibration states of the diaphragms are mutually counteracted to keep stable by utilizing the characteristic that external noise coupled into the air cavities on the two sides of the probe has the same amplitude but opposite phases on the acting force of the cantilever type sound wave sensitive diaphragms, so that the effect of resisting external noise interference is achieved. The single cantilever type sound wave sensitive diaphragm is used as a signal sensing element and is also used for noise elimination, and a traditional structure and a signal processing process based on a double-cantilever differential noise reduction scheme are simplified. The scheme of the invention has the advantages of simple structure, high sensitivity, fast response speed and strong stability in a strong noise environment.

Description

Technical Field

[0001] The invention belongs to the technical field of photoacoustic spectroscopy gas sensing, and relates to an optical fiber photoacoustic gas sensing system and method for suppressing environmental noise interference. Background Art

[0002] Fiber optic photoacoustic gas sensing technology has the advantages of intrinsic safety, anti-electromagnetic interference, small size and high sensitivity, and is very suitable for gas detection in various complex environments. Among them, the sensitivity of the acoustic wave sensitive element is the core factor that determines the detection index of the sensing system. By selecting an acoustic wave sensitive element with higher sensitivity, the detection index of the fiber optic photoacoustic gas sensor can be effectively improved. However, the high sensitivity of the system is also accompanied by a decrease in stability, which makes the sensor more susceptible to external interference and detection. For example, in the field of dissolved gas analysis, there is strong noise interference around large electrical equipment; in petrochemical and coal mining environments, the noise of heavy excavation equipment and low-frequency noise signal interference in the environment will seriously affect the accuracy and reliability of the photoacoustic detection device. In addition, wind disturbance and mechanical damage in open-air environments are also important factors affecting detection stability. The differential principle is a simple and effective interference suppression method. In the literature Differential cantileversenhanced fiber-optic photoacoustic sensor for diffusion gas detection. Analytical Chemistry, 96.11(2024):4562–4569, a differential cantilever enhanced fiber-optic photoacoustic sensor for diffusion gas detection is proposed to solve the problem that fiber-optic photoacoustic sensors are easily disturbed by external vibration and noise. The sensor consists of two photoacoustic tubes of the same size and a pair of differential interference cantilevers. One of the cantilevers detects the photoacoustic signal containing external noise interference, and the other cantilever is only used to detect external noise. The environmental noise interference is suppressed by differentially detecting the signals detected by the two cantilevers. However, the dual cantilever differential detection scheme requires that the acoustic sensitivity of the two cantilevers is consistent and the vibration phase is the same, which is difficult to ensure in actual processing and manufacturing. At the same time, the dual cantilevers need to be demodulated at the same time, which also increases the complexity of the demodulation system. Therefore, it is of great application significance to design a fiber-optic photoacoustic gas sensing system and method with high stability and simple structure to suppress environmental noise interference. Summary of the invention

[0003] The purpose of the present invention is to propose a fiber optic photoacoustic gas sensing system and method for suppressing environmental noise interference. The scheme has a simple structure, high sensitivity and strong stability in a strong noise environment. It can effectively solve the problems of traditional fiber optic photoacoustic sensors being easily interfered by environmental noise and poor system complexity, and further expand the application of fiber optic photoacoustic sensing technology in complex interference environments.

[0004] The principle of the present invention is as follows: the symmetrical fiber photoacoustic sensor probe shown in the attached figure takes the cantilever type acoustic wave sensitive diaphragm as the symmetry axis, and the air cavity structures on both sides are exactly the same, which serve as the signal cavity and the reference cavity respectively. Since the laser is transmitted only in the air cavity (signal cavity) on one side of the cantilever type acoustic wave sensitive diaphragm, the photoacoustic signal proportional to the gas concentration is only generated in the signal cavity. Since the air cavities on both sides are symmetrical structures, the noise amplitude and phase coupled into the signal cavity and the reference cavity are the same. In this case, the photoacoustic signal acts on the cantilever type acoustic wave sensitive diaphragm from one direction to make it vibrate, while the environmental noise vibrates the cantilever type acoustic wave sensitive diaphragm from two directions with the same force, and the diaphragm vibrates in opposite directions, which causes the two vibration states to cancel each other out so that the diaphragm remains stable. Therefore, the sensor probe can only respond to the photoacoustic signal and suppress the interference of environmental noise.

[0005] The technical solution of the present invention:

[0006] The invention discloses an optical fiber photoacoustic gas sensing system for suppressing environmental noise interference, comprising a narrow linewidth laser 1, a dual-core optical fiber 2, a symmetrical optical fiber photoacoustic sensing probe 3, a wide-spectrum detection light source 4, an optical circulator 5, a spectrometer 6 and a control circuit 7; the control circuit 7 is respectively connected to the narrow linewidth laser 1 and the spectrometer 6, the narrow linewidth laser 1 is respectively connected to the symmetrical optical fiber photoacoustic sensing probe 3 and the optical circulator 5 through the dual-core optical fiber 2, and the optical circulator 5 is respectively connected to the wide-spectrum detection light source 4 and the spectrometer 6; the control circuit 7 drives the narrow linewidth laser 1 to output laser light, which is connected to the symmetrical optical fiber acoustic wave sensing probe 3 through the dual-core optical fiber 2; the wide-spectrum light emitted by the wide-spectrum detection light source 4 enters the dual-core optical fiber 2 through the optical circulator 5, interferes in the symmetrical optical fiber photoacoustic sensing probe 3, the returned interference signal is transmitted to the spectrometer 6 through the optical circulator 5, and the interference spectrum is transmitted to the control circuit 7 for processing and display.

[0007] The symmetrical fiber optic photoacoustic sensor probe 3 includes a signal channel laser collimator 8A, a reference channel laser collimator 8B, a signal cavity 9, a reference cavity 10, a cantilever type acoustic wave sensitive diaphragm 11, a signal channel ceramic pin 12A, a reference channel ceramic pin 12B, a signal channel diffusion hole 13A and a reference channel diffusion hole 13B; the symmetrical fiber optic photoacoustic sensor probe 3 as a whole takes the cantilever type acoustic wave sensitive diaphragm 11 as the symmetry axis, the signal channel laser collimator 8A and the reference channel laser collimator 8B are symmetrically located at both ends of the symmetrical fiber optic photoacoustic sensor probe 3, and the two are the same; the signal channel laser collimator 8A and the reference channel laser collimator 8B are respectively connected to the signal cavity 9 and the reference cavity 10; the signal channel ceramic pin 12A and the reference channel ceramic pin 12B are symmetrically arranged in the symmetrical fiber optic photoacoustic sensor probe 3, and the two are the same; The ceramic pin 12A and the reference channel ceramic pin 12B are located at the outside of the signal cavity 9 and the reference cavity 10 respectively. The end faces of the signal channel ceramic pin 12A and the reference channel ceramic pin 12B are aligned with the free end of the cantilever type acoustic wave sensitive diaphragm 11 to form two FP microcavities with the same cavity length. The two FP microcavities are connected to the air at the ends of the signal cavity 9 and the reference cavity 10; the signal cavity 9 and the reference cavity 10 are symmetrically arranged in the symmetrical optical fiber photoacoustic sensor probe 3, and the two are the same; the signal channel diffusion hole 13A and the reference channel diffusion hole 13B are symmetrically opened on the side wall of the symmetrical optical fiber photoacoustic sensor probe 3, and the two are the same; the signal channel diffusion hole 13A and the reference channel diffusion hole 13B are respectively connected to the signal cavity 9 and the reference cavity 10, and the diameter of the signal channel diffusion hole 13A and the reference channel diffusion hole 13B is less than 1.5 mm and the depth does not exceed 5 mm.

[0008] The control circuit 7 includes the functions of spectrum acquisition, fast Fourier transform, digital phase-locked amplification and driving narrow linewidth laser.

[0009] The wide-spectrum detection light source 4 is a near-infrared broadband light source with a central wavelength of 1550 nm and a spectrum width of not less than 40 nm.

[0010] The wavelength range of the spectrometer 6 is 1525-1570 nm, and the frame rate is higher than 15 kHz.

[0011] The signal channel ceramic pin 12A and the reference channel ceramic pin 12B have the same length from the cantilever type acoustic wave sensitive diaphragm 11 and are in the range of 0.15 mm to 1 mm.

[0012] A fiber optic photoacoustic gas sensing method for suppressing environmental noise interference, laser is incident on a symmetrical fiber optic photoacoustic sensor probe 3, exciting the gas to be measured to generate a photoacoustic signal, causing the cantilever type acoustic wave sensitive diaphragm 11 to vibrate, and the noise is coupled into the signal cavity 9 and the reference cavity 10, acting on both sides of the cantilever type acoustic wave sensitive diaphragm 11 with the same force and being offset; a wide spectrum detection light source 4 is incident on the symmetrical fiber optic photoacoustic sensor probe 3 to cause interference, and the vibration of the cantilever type acoustic wave sensitive diaphragm 11 causes the phase change of the interference spectrum to be detected by the spectrometer 6 and the photoacoustic signal amplitude is demodulated by the control circuit 7. The specific steps are as follows:

[0013] First, the gas to be measured and the environmental noise enter the signal cavity 9 and the reference cavity 10 in the symmetrical optical fiber photoacoustic sensor probe 3 through the signal channel diffusion hole 13A and the reference channel diffusion hole 13B; the control circuit 7 drives the narrow linewidth laser 1, and the laser emitted by the narrow linewidth laser 1 is coupled into the symmetrical optical fiber photoacoustic sensor probe 3 through the dual-core optical fiber 2, and then is collimated by the signal channel laser collimator 8A and incident into the signal cavity 9 to stimulate the photoacoustic signal, and the photoacoustic signal causes the cantilever type acoustic wave sensitive diaphragm 11 to vibrate; in addition, the external environmental noise is transmitted from the cantilever type acoustic wave sensitive diaphragm 11 The cantilever-type acoustic wave sensitive diaphragm 11 is vibrated in two opposite directions by the same force on both sides, which causes the two vibration states to cancel each other out, so that the vibration of the cantilever-type acoustic wave sensitive diaphragm 11 is only related to the photoacoustic signal. In order to ensure that the amplitude of the cantilever vibration caused by the same amplitude and phase force on both sides of the cantilever is the same, the signal cavity 9 and the reference cavity 10 are completely consistent in structure, the reference channel laser collimator 8B is installed at a symmetrical position of the signal channel laser collimator 8A, and the reference channel ceramic pin 12B is installed at a symmetrical position of the signal channel ceramic pin 12A.

[0014] Then, the cantilever acoustic wave sensitive diaphragm 11 and the signal channel ceramic pin 12A form a micro Fabry-Perot (FP) interference cavity. The wide-spectrum light emitted by the wide-spectrum detection light source 4 passes through the optical circulator 5 and the dual-core optical fiber 2, and FP interference occurs between the inner surface of the cantilever acoustic wave sensitive diaphragm 11 and the end face of the signal channel ceramic pin 12A. When the cantilever acoustic wave sensitive diaphragm 11 vibrates, the FP cavity length changes, thereby causing a phase change in the interference spectrum; the interference light is transmitted into the spectrometer 6 through the dual-core optical fiber 2 and the optical circulator 5, and the control circuit 7 collects the interference spectrum information and demodulates the FP cavity length, thereby inverting the concentration of the gas.

[0015] The beneficial effects of the present invention are as follows: the air cavity structures on both sides of the symmetrical fiber optic photoacoustic sensor probe are consistent and in opposite directions. The external noise coupled into the air cavities on both sides of the probe exerts the same force amplitude but opposite phase on the cantilever-type acoustic wave sensitive diaphragm, so that the vibration states of the diaphragm cancel each other out and remain stable, thereby achieving the effect of resisting external noise interference. The single cantilever-type acoustic wave sensitive diaphragm itself serves as both a signal sensing element and a noise reducer, which simplifies the structure and signal processing process of the traditional dual-cantilever differential noise reduction solution. The scheme of the present invention has the advantages of simple structure, high sensitivity, fast response speed and strong stability in a strong noise environment, providing a highly competitive technical solution for trace gas sensing in complex industrial environments and strong noise environments using fiber optic photoacoustic gas sensing technology. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 It is a schematic diagram of the system structure of the present invention.

[0017] Figure 2 It is a schematic diagram of a symmetrical fiber optic photoacoustic gas sensing probe.

[0018] In the figure: 1 narrow linewidth laser; 2 dual-core optical fiber; 3 symmetrical optical fiber photoacoustic sensor probe; 4 wide spectrum detection light source; 5 optical circulator; 6 spectrometer; 7 control circuit; 8A signal channel laser collimator; 8B reference channel laser collimator; 9 signal cavity; 10 reference cavity; 11 cantilever type acoustic wave sensitive diaphragm; 12A signal channel ceramic pin; 12B reference channel ceramic pin; 13A signal channel diffusion hole; 13B reference channel diffusion hole. DETAILED DESCRIPTION

[0019] The specific implementation of the present invention is described in detail below in conjunction with the technical scheme and the accompanying drawings.

[0020] A fiber photoacoustic gas sensing system for suppressing environmental noise interference mainly comprises a narrow linewidth laser 1, a dual-core optical fiber 2, a symmetrical optical fiber photoacoustic sensing probe 3, a wide-spectrum detection light source 4, an optical circulator 5, a spectrometer 6, and a control circuit 7. The gas to be measured and the environmental noise are coupled into the symmetrical optical fiber photoacoustic sensing probe 3, and the noise is offset due to the symmetrical structure; the control circuit 7 drives the narrow linewidth laser 1 to emit laser light, which is transmitted through the dual-core optical fiber 2 to the symmetrical optical fiber photoacoustic sensing probe 3 to generate a photoacoustic signal; the wide-spectrum light emitted by the wide-spectrum detection light source 4 enters the dual-core optical fiber 2 through the optical circulator 5, and interference occurs in the symmetrical optical fiber photoacoustic sensing probe 3, and the interference light contains the amplitude information of the photoacoustic signal, and the returned interference light is transmitted to the spectrometer 6 through the optical circulator 5, and the interference spectrum is transmitted to the control circuit 7 for processing and display.

[0021] The narrow linewidth laser light source 1 is a distributed feedback (DFB) laser with a central wavelength of 1532.83 nm and a power of 20 mW. The wide spectrum detection light source 4 is an SLD light source with a central wavelength of 1550 nm and a bandwidth of 50 nm. The spectrometer 6 is a high-speed micro-spectrometer with a spectrum acquisition rate of 15 kHz.

[0022] The symmetrical optical fiber photoacoustic sensor probe 3 includes a signal channel laser collimator 8A, a reference channel laser collimator 8B, a signal cavity 9, a reference cavity 10, a cantilever acoustic wave sensitive diaphragm 11, a signal channel ceramic pin 12A, a reference channel ceramic pin 12B, a signal channel diffusion hole 13A, and a reference channel diffusion hole 13B. The diameter of the signal cavity 9 and the reference cavity 10 is 4 mm, and the length is 10 mm. The diameter of the signal channel diffusion hole 13A and the reference channel diffusion hole 13B is 1 mm, and the length is 3 mm. The distance between the signal channel ceramic pin 12A and the channel ceramic pin 12B and the cantilever acoustic wave sensitive diaphragm 11 is 0.5 mm. The cantilever acoustic wave sensitive diaphragm 11 is made of silicon, and the width of the slit of the rectangular cantilever beam etched thereon is about 6 μm. The cantilever beam is 1.8 mm long, 0.8 mm wide, and 6 μm thick.

[0023] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. For those skilled in the art, the present invention may have various modifications and variations. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A fiber optic photoacoustic gas sensing system for suppressing environmental noise interference, characterized in that: The optical fiber photoacoustic gas sensing system comprises a narrow line width laser (1), a dual-core optical fiber (2), a symmetrical optical fiber photoacoustic sensing probe (3), a wide spectrum detection light source (4), an optical circulator (5), a spectrometer (6) and a control circuit (7); the control circuit (7) is respectively connected to the narrow line width laser (1) and the spectrometer (6); the narrow line width laser (1) is respectively connected to the symmetrical optical fiber photoacoustic sensing probe (3) and the optical circulator (5) through the dual-core optical fiber (2); the optical circulator (5) is respectively connected to the wide spectrum detection light source (4) and the spectrometer (6); the control circuit (7) drives the narrow line width laser (1) to output laser light, which is connected to the symmetrical optical fiber acoustic wave sensing probe 3 through the dual-core optical fiber (2); the wide spectrum light emitted by the wide spectrum detection light source (4) enters the dual-core optical fiber (2) through the optical circulator (5), interferes in the symmetrical optical fiber photoacoustic sensing probe (3), the returned interference signal is transmitted to the spectrometer (6) through the optical circulator (5), and the interference spectrum is transmitted to the control circuit (7) for processing and display.

2. The optical fiber photoacoustic gas sensing system according to claim 1, characterized in that: The symmetrical fiber optic photoacoustic sensor probe (3) comprises a signal channel laser collimator (8A), a reference channel laser collimator (8B), a signal cavity (9), a reference cavity (10), a cantilever type acoustic wave sensitive diaphragm (11), a signal channel ceramic pin (12A), a reference channel ceramic pin (12B), a signal channel diffusion hole (13A) and a reference channel diffusion hole (13B); the symmetrical fiber optic photoacoustic sensor probe (3) as a whole takes the cantilever type acoustic wave sensitive diaphragm (11) as a symmetry axis, the signal channel laser collimator (8A) and the reference channel laser collimator (8B) are symmetrically located at two ends of the symmetrical fiber optic photoacoustic sensor probe (3), and the two are identical; the signal channel laser collimator (8A) and the reference channel laser collimator (8B) are respectively connected to the signal cavity (9) and the reference cavity (10); the signal channel ceramic pin (12A) and the reference channel ceramic pin (12B) are connected to the symmetrical fiber optic photoacoustic sensor probe (3) The acoustic sensor probe (3) is symmetrically arranged, and the two are identical; the signal channel ceramic pin (12A) and the reference channel ceramic pin (12B) are correspondingly located outside the signal cavity (9) and the reference cavity (10), and the ends of the signal channel ceramic pin (12A) and the reference channel ceramic pin (12B) face the free end of the cantilever acoustic wave sensitive diaphragm (11), forming two FP microcavities with the same cavity length, and the two FP microcavities are connected to the air at the ends of the signal cavity (9) and the reference cavity (10); the signal cavity (9) and the reference cavity (10) are symmetrically arranged in the symmetrical optical fiber photoacoustic sensor probe (3), and the two are identical; the signal channel diffusion hole (13A) and the reference channel diffusion hole (13B) are symmetrically opened on the side wall of the symmetrical optical fiber photoacoustic sensor probe (3), and the two are identical; the signal channel diffusion hole (13A) and the reference channel diffusion hole (13B) are respectively connected to the signal cavity (9) and the reference cavity (10).

3. The optical fiber photoacoustic gas sensing system according to claim 1, characterized in that: The signal channel diffusion hole (13A) and the reference channel diffusion hole (13B) have a diameter less than 1.5 mm and a depth not exceeding 5 mm.

4. The fiber optic photoacoustic gas sensing system according to claim 1, characterized in that: The control circuit (7) includes the functions of spectrum acquisition, fast Fourier transform, digital phase-locked amplification and driving a narrow linewidth laser.

5. The fiber optic photoacoustic gas sensing system according to claim 1, characterized in that: The wide-spectrum detection light source (4) is a near-infrared broadband light source with a central wavelength of 1550 nm and a spectrum width of not less than 40 nm.

6. The fiber optic photoacoustic gas sensing system according to claim 1, characterized in that: The wavelength range of the spectrometer (6) is 1525-1570 nm, and the frame rate is higher than 15 kHz.

7. The fiber optic photoacoustic gas sensing system according to claim 1, characterized in that: The signal channel ceramic pin (12A) and the reference channel ceramic pin (12B) are at the same distance from the cantilever type acoustic wave sensitive diaphragm (11) in length, and the range is 0.15 mm to 1 mm.

8. A fiber optic photoacoustic gas sensing method for suppressing environmental noise interference, characterized in that: The steps are as follows: laser is incident on a symmetrical optical fiber photoacoustic sensor probe (3), exciting the gas to be measured to generate a photoacoustic signal, causing the cantilever type acoustic wave sensitive diaphragm (11) to vibrate, and noise is coupled into a signal cavity (9) and a reference cavity (10), acting on both sides of the cantilever type acoustic wave sensitive diaphragm (11) with the same force and being offset; a wide spectrum detection light source (4) is incident on the symmetrical optical fiber photoacoustic sensor probe (3) to cause interference, and the vibration of the cantilever type acoustic wave sensitive diaphragm (11) causes the phase change of the interference spectrum to be detected by a spectrometer (6), and the photoacoustic signal amplitude is demodulated by a control circuit (7); the specific steps are as follows: First, the gas to be measured and the environmental noise enter the signal cavity (9) and the reference cavity (10) in the symmetrical optical fiber photoacoustic sensor probe (3) through the signal channel diffusion hole (13A) and the reference channel diffusion hole (13B); the control circuit (7) drives the narrow line width laser (1), and the laser emitted by the narrow line width laser (1) is coupled into the symmetrical optical fiber photoacoustic sensor probe (3) through the double-core optical fiber (2), and then is collimated by the signal channel laser collimator (8A) and incident into the signal cavity (9) to stimulate the photoacoustic signal, and the photoacoustic signal causes the cantilever type acoustic wave sensitive diaphragm (11) to vibrate; in addition, the external environmental noise is transmitted from the cantilever type acoustic wave sensitive diaphragm (11) to the cantilever type acoustic wave sensitive diaphragm (11). The cantilever-type acoustic wave sensitive diaphragm (11) is vibrated in two opposite directions by the same force on both sides of the diaphragm (11), which causes the two vibration states to cancel each other out, thereby causing the vibration of the cantilever-type acoustic wave sensitive diaphragm (11) to be only related to the photoacoustic signal. In order to ensure that the amplitude of the cantilever vibration caused by the same amplitude and phase force on both sides of the cantilever is the same, the signal cavity (9) and the reference cavity (10) have completely the same structure, the reference channel laser collimator (8B) is installed at a symmetrical position of the signal channel laser collimator (8A), and the reference channel ceramic pin (12B) is installed at a symmetrical position of the signal channel ceramic pin (12A); Then, the cantilever type acoustic wave sensitive diaphragm (11) and the signal channel ceramic plug pin (12A) form a micro Fabry-Perot interference cavity. The wide-spectrum light emitted by the wide-spectrum detection light source (4) passes through the optical circulator (5) and the dual-core optical fiber (2), and FP interference occurs between the inner surface of the cantilever type acoustic wave sensitive diaphragm (11) and the end face of the signal channel ceramic plug pin (12A). When the cantilever type acoustic wave sensitive diaphragm (11) vibrates, the FP cavity length changes, thereby causing a phase change in the interference spectrum. The interference light is transmitted into the spectrometer (6) through the dual-core optical fiber (2) and the optical circulator (5), and the control circuit (7) collects the interference spectrum information and demodulates the FP cavity length, thereby inverting the concentration of the gas.

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