Fiber-optic photoacoustic sensing probe capable of resisting interference from ambient noise, and sensing system

Patent metadata

Field	Value
Publication number	US-11940375-B2
Application number	US-202117535978-A
Country	US
Kind code	B2
Filing date	Nov 26, 2021
Priority date	Dec 8, 2020
Publication date	Mar 26, 2024
Grant date	Mar 26, 2024

Abstract

The present disclosure relates to the technical field of fiber-optic gas sensing and laser photoacoustic spectroscopy, and reliability of a gas detection system is improved by actively selecting a working frequency of low noise interference combined with an optical fiber photoacoustic sensing probe capable of isolating high-frequency noise. A gas enters a photoacoustic microcavity through gaps on a sound-sensitive diaphragm after diffusing into a miniature air chamber through a plurality of micropores. Photoacoustic excitation light is incident into the photoacoustic microcavity through a fiber-optic collimator and then excited to generate a photoacoustic pressure wave to cause the sound-sensitive diaphragm to vibrate periodically. An end face of a single-mode optical fiber and the sound-sensitive diaphragm constitutes a fiber-optic Fabry-Perot interferometer. The interferometer measures a deflection of the diaphragm and inverts a concentration of the to-be-measured gas.

First claim

The invention claimed is:

1. A fiber-optic photoacoustic sensing probe capable of resisting interference from ambient noise, comprising a fiber-optic collimator ( 9 ), a single-mode optical fiber ( 10 ), a photoacoustic microcavity ( 11 ), a miniature air chamber ( 12 ), a diffusion micropore ( 13 ), a sound-sensitive diaphragm ( 14 ), and a sound-insulated housing ( 15 ), wherein the miniature air chamber ( 12 ) is provided inside the sound-insulated housing ( 15 ), the miniature air chamber ( 12 ) is cylindrical, and a plurality of diffusion micropores ( 13 ) communicating with the outside are provided along a diameter direction of the miniature air chamber ( 12 ); the sound-sensitive diaphragm ( 14 ) is installed inside the miniature air chamber ( 12 ), and comprises a plurality of gaps ( 141 ) that constitute a cross-shaped beam structure at a central position of the sound-sensitive diaphragm ( 14 ); the photoacoustic microcavity ( 11 ) is deployed inside the sound-insulated housing ( 15 ) along a direction perpendicular to the miniature air chamber ( 12 ), one end of the photoacoustic microcavity ( 11 ) is connected to the outside, and the other end of the photoacoustic microcavity ( 11 ) is connected to the miniature air chamber ( 12 ); the fiber-optic collimator ( 9 ) is sealed and installed on the end, connected to the outside, of the photoacoustic microcavity ( 11 ); the single-mode optical fiber ( 10 ) is connected to the miniature air chamber ( 12 ) along a horizontal center line of the sound-insulated housing ( 15 ); and a center of the sound-sensitive diaphragm ( 14 ) and an end face of the single-mode optical fiber ( 10 ) constitute a fiber-optic Fabry-Perot interferometer.

2. The fiber-optic photoacoustic sensing probe capable of resisting interference from ambient noise according to claim 1 , wherein a working process is as follows: a gas enters the photoacoustic microcavity ( 11 ) through the gaps ( 141 ) on the sound-sensitive diaphragm ( 14 ) after diffusing into the miniature air chamber ( 12 ) through the plurality of diffusion micropores ( 13 ); photoacoustic excitation light is incident into the photoacoustic microcavity ( 11 ) through the fiber-optic collimator ( 9 ), and then excited to generate a photoacoustic pressure wave to cause the sound-sensitive diaphragm ( 14 ) to vibrate periodically; and a deflection of the diaphragm is measured by using the fiber-optic Fabry-Perot interferometer, and a concentration of the to-be-measured gas is inverted.

3. A sensing system using the fiber-optic photoacoustic sensing probe capable of resisting interference from ambient noise according to claim 2 , comprising: a signal collection and processing circuit ( 1 ), a laser light source drive circuit ( 2 ), a photoacoustic excitation light source ( 3 ), a double-core optical fiber ( 4 ), a fiber-optic photoacoustic sensing probe ( 5 ), a detection light source ( 6 ), a fiber-optic circulator ( 7 ), and a photodetector ( 8 ), wherein an input terminal of the photodetector ( 8 ) is connected to port 3# of the fiber-optic circulator ( 7 ), and an output terminal of the photodetector ( 8 ), the signal collection and processing circuit ( 1 ), the laser light source drive circuit ( 2 ), and the photoacoustic excitation light source ( 3 ) are connected in series and then connected to the fiber-optic photoacoustic sensing probe ( 5 ) by using one optical fiber of the double-core optical fiber ( 4 ); the detection light source ( 6 ) is connected to port 1# of the fiber-optic circulator ( 7 ), and port 2# of the fiber-optic circulator ( 7 ) is connected to the fiber-optic photoacoustic sensing probe ( 5 ) by using the other optical fiber of the double-core optical fiber ( 4 ); and the signal collection and processing circuit ( 1 ) adopts a digital lock-in amplifier based on a field programmable gate array (FPGA).

4. The sensing system according to claim 3 , wherein a working process comprises the following steps:
step 1: turning off the photoacoustic excitation light source ( 3 ), wherein the detection light is reflected on a surface of the fiber-optic Fabry-Perot interferometer after entering the fiber-optic photoacoustic sensing probe ( 5 ), to output an interference signal;
step 2: performing demodulation and spectrum analysis on the output interference signal to obtain influence of ambient noise, and then determining a low-interference frequency as a working frequency;
step 3: driving the photoacoustic excitation light source ( 3 ) after determining a modulation frequency, wherein the excitation light is incident into the fiber-optic photoacoustic sensing probe ( 5 ) to cause a photoacoustic effect and generate a photoacoustic signal;
step 4: restoring the photoacoustic signal by using an interference-intensity demodulation method, and performing spectrum analysis on the signal; and
step 5: calculating a concentration of a to-be-measured gas based on an amplitude of the photoacoustic signal.

5. The sensing system according to claim 4 , wherein a method for determining the low-interference frequency as the working frequency in step 2 is as follows: the detection light emitted by the detection light source ( 6 ) is incident into the fiber-optic photoacoustic sensing probe ( 5 ) after passing through the fiber-optic circulator ( 7 ), and returned Fabry-Perot interference signal light is received by the photodetector ( 8 ) after passing through the fiber-optic circulator ( 7 ); the signal collection and processing circuit ( 1 ) collects a photoelectric signal converted by the photodetector ( 8 ), restores an acoustic wave signal by using the interference-intensity demodulation method, and performs spectrum analysis on the detected ambient noise through fast Fourier transform; and the low-interference frequency in the ambient noise is selected, within a high frequency range and based on a frequency response of the fiber-optic photoacoustic sensing probe ( 5 ) to an external acoustic wave and a spectrum analysis result, as the working frequency of photoacoustic measurement.

6. The sensing system according to claim 4 , wherein the modulation frequency in step 3 is set to half of the working frequency.

7. The sensing system according to claim 4 , wherein the restoring the photoacoustic signal by using an interference-intensity demodulation method specifically comprises: setting a central wavelength of the detection light source ( 6 ) to lock a working point at a position with a maximum absolute value of a slope of an interference curve of the fiber-optic Fabry-Perot interferometer used for photoacoustic detection in the fiber-optic photoacoustic sensing probe ( 5 ), so that acoustic wave detection has the highest sensitivity and a largest linear response range.

8. The sensing system according to claim 3 , wherein the photoacoustic excitation light source ( 3 ) is a near-infrared wavelength-tunable narrow-linewidth laser light source that can be coupled to the single-mode optical fiber.

9. The sensing system according to claim 3 , wherein the double-core optical fiber ( 4 ) is composed of two G652 single-mode optical fibers.

10. The sensing system according to claim 3 , wherein the detection light source ( 6 ) is a wavelength-tunable narrow-linewidth laser light source.

11. A sensing system using the fiber-optic photoacoustic sensing probe capable of resisting interference from ambient noise according to claim 1 , comprising: a signal collection and processing circuit ( 1 ), a laser light source drive circuit ( 2 ), a photoacoustic excitation light source ( 3 ), a double-core optical fiber ( 4 ), a fiber-optic photoacoustic sensing probe ( 5 ), a detection light source ( 6 ), a fiber-optic circulator ( 7 ), and a photode

Assignees

• State Grid Anhui Electric Power Res Institute
• Univ Dalian Tech

Inventors

• Ma Fengxiang
• Chen Ke
• Zhao Yue
• Zhu Feng
• Guo Min
• Tian Yu
• Yuan Xiaofang
• Ma Yabin
• Hang Chen

Classifications

• G01N21/1702 Primary

  with opto-acoustic detection, e.g. for gases or analysing solids · CPC title

• G01N33/0027 Primary

  concerning the detector · CPC title

• G01N2021/1704

  in gases · CPC title

• G01N2201/06113

  Coherent sources; lasers · CPC title

• G01N2201/08

  Optical fibres; light guides · CPC title