CN-117705725-B - Multistage coupling amplification photoacoustic spectrum greenhouse gas measurement system and method

CN117705725BCN 117705725 BCN117705725 BCN 117705725BCN-117705725-B

Abstract

The invention discloses a multistage coupling amplification photoacoustic spectrum greenhouse gas measurement system and a method, and belongs to the technical field of trace gas measurement; the measuring system comprises a miniature multi-pass variable-diameter T-shaped photoacoustic cell, a gas distribution system, a DFB laser and a data acquisition and processing system, wherein a first reflecting mirror and a second reflecting mirror are respectively arranged at two side windows of the miniature multi-pass variable-diameter T-shaped photoacoustic cell, the gas distribution system is used for leading gas to be measured into and filling a gas chamber of the miniature multi-pass variable-diameter T-shaped photoacoustic cell, the DFB laser generates modulated laser, the modulated laser enters the miniature multi-pass variable-diameter T-shaped photoacoustic cell from an incident hole of the first reflecting mirror through a collimating lens and is reflected back and forth between the second reflecting mirrors, so that a multi-stage coupling amplified photoacoustic signal is generated, then the photoacoustic signal is demodulated by a phase-locked amplifier and enters the data acquisition and processing system, and the interaction between the laser and the gas is enhanced through multiple reflections in the miniature multi-pass variable-diameter T-shaped photoacoustic cell, so that the monitoring of methane gas concentration is more accurate and reliable.

Inventors

Zha Shenlong
CHEN HANG
MA HONGLIANG
PAN PAN
ZHANG QILEI
Dong Jiadong
LI LINGLI
GAO RAN

Assignees

安庆师范大学
安徽理工大学
安徽创孚医疗科技有限公司

Dates

Publication Date: 20260512
Application Date: 20231229

Claims (8)

1. The multi-stage coupling amplification photoacoustic spectrum greenhouse gas measurement system is characterized by comprising a miniature multi-pass variable-diameter T-shaped photoacoustic cell (12), a gas distribution system (17), a DFB laser (3), a collimating lens (6), a data acquisition card (9) and a computer (18), wherein a first reflecting mirror (10) and a second reflecting mirror (11) with an inlet hole are respectively arranged at two side windows of the miniature multi-pass variable-diameter T-shaped photoacoustic cell (12); The gas distribution system (17) is used for leading gas to be tested into and filling the gas chamber of the miniature multi-pass variable-diameter T-shaped photoacoustic cell (12), the DFB laser (3) generates modulated laser, the modulated laser enters the miniature multi-pass variable-diameter T-shaped photoacoustic cell (12) from the incident hole of the first reflecting mirror (10) through the collimating lens (6) and is reflected back and forth between the collimating lens and the second reflecting mirror (11), a plurality of light spots are formed on the mirror surface, the laser is emitted from the incident hole of the first reflecting mirror (10), a multi-stage amplified photoacoustic signal is generated in the miniature multi-pass variable-diameter T-shaped photoacoustic cell (12), and then the signal is acquired by the data acquisition card (9) after the signal is received by the acoustic detector and demodulated by the lock-in amplifier, and finally the computer (18) is used for data processing and operation; The gas to be measured absorbs and modulates the light source to generate a heat source And generate a photoacoustic signal, which can be used as sound pressure The mathematical model is expressed as: In the formula, In order for the laplace operator to be useful, As the displacement vector of the object to be displaced, Is a heat capacity ratio of the heat energy and the water energy, 、 Respectively equal heat capacity and equal heat capacity, For the propagation speed of light in the gas, Is the thermal power density; In the cylindrical coordinate system, normal mode Lower resonant frequency Amplitude of (2) Can be expressed as: In the formula, Is in normal mode Is used for the resonance frequency of the (c) wave, Is that Is used for the complex conjugate of (a), For the volume of the photoacoustic cell resonator tube, Is of mode Is used for the quality factor of (a), Laser power, c is gas concentration, integral Indicating the degree of coupling of the light intensity distribution to the normal mode A representation; At the position of The generated sound pressure is strongest under the resonance condition, and the sound pressure at rM in the miniature multi-path variable-diameter T-shaped photoacoustic cell (12) is obtained as follows: In the formula, For the constant of the photoacoustic cell A representation; after the acoustic detector is introduced, a detected photoacoustic signal is generated in the miniature multi-path variable-diameter T-shaped photoacoustic cell (12) The method comprises the following steps: In the formula, Is the sensitivity of the acoustic detector.
2. The multi-stage coupling amplification photoacoustic spectroscopy greenhouse gas measurement system of claim 1, further comprising a function generator (4), a lock-in amplifier (5), an adder (1) and a laser controller (2), wherein the modulation of the light source generates a low-frequency triangular wave for scanning a gas absorption line through the function generator (4), and the lock-in amplifier (5) generates a high-frequency sine for emitting light modulation, and the laser generated by the DFB laser (3) is subjected to wavelength modulation by adding the adder (1) and then is input to the laser controller (2) so that the output wavelength of the laser is positioned at the center of an absorption line of a gas to be measured.
3. The multi-stage coupling amplification photoacoustic spectrum greenhouse gas measurement system according to claim 2, further comprising a microphone (8) and a preamplifier (7), wherein an acoustic signal which can be received by the high-sensitivity microphone is generated in the miniature multi-pass variable-diameter T-shaped photoacoustic cell (12), the acoustic signal is converted into an electric signal through the microphone (8), and the electric signal is demodulated by the phase-locked amplifier (5) after passing through the preamplifier (7) to extract a second harmonic signal.
4. A multi-stage coupling amplified photoacoustic spectroscopy greenhouse gas measurement system according to claim 1 or 3, wherein the gas concentration measurement is performed by calibrating a photoacoustic signal of the gas to be measured generated in the miniature multi-pass variable-diameter T-type photoacoustic cell (12) with a standard gas of known concentration, performing linear fitting, and inverting the amplitude of the photoacoustic signal in combination with a computer (18) to calculate the concentration of the gas to be measured.
5. The multi-stage coupling amplified photoacoustic spectrum greenhouse gas measurement system according to claim 3, wherein the miniature multi-path variable-diameter T-shaped photoacoustic cell (12) is provided with an air inlet (13) and an air outlet (14), the air inlet (13) is connected with an air distribution system (17), the measurement system is also provided with a miniature air pump (19), and the miniature air pump (19) is connected with the air outlet (14) and can pump the measured methane gas out of the miniature multi-path variable-diameter T-shaped photoacoustic cell (12).
6. The multi-stage coupling amplification photoacoustic spectrum greenhouse gas measurement system according to claim 5, wherein an air inlet air valve (16) is arranged between the air inlet (13) and the air distribution system (17), and an air outlet air valve (15) is arranged between the air outlet (14) and the micro air pump (19).
7. The multi-stage coupling amplified photoacoustic spectroscopy greenhouse gas measurement system of claim 1, wherein the miniature multi-pass reducing T-shaped photoacoustic cell (12) is fabricated using 3D printing techniques.
8. A multi-stage coupling amplified photoacoustic spectroscopy greenhouse gas measurement method using the measurement system of claim 6, comprising the steps of: S1, opening an air inlet air valve (16), and filling methane gas into a miniature multi-path variable-diameter T-shaped photoacoustic cell (12) by using an air distribution system (17); S2, generating a low-frequency triangular wave for scanning a methane gas absorption line through a function generator (4), generating a high-frequency sine wave for light modulation through a lock-in amplifier (5), adding the high-frequency sine wave through an adder (1), and inputting the high-frequency sine wave to a laser controller (2) to perform wavelength modulation on laser generated by a DFB laser (3) so that the output wavelength of the laser is positioned at the center of an absorption spectrum line of methane gas to be detected; S3, the modulated laser enters an air chamber of a miniature multi-pass variable-diameter T-shaped photoacoustic cell (12) printed in a 3D mode from an incident hole of a first reflecting mirror (10) through a collimating lens (6), is reflected back and forth between the two surfaces of the reflecting mirror (11), generates multilevel coupling amplified photoacoustic signals in the miniature multi-pass variable-diameter T-shaped photoacoustic cell (12), is received by a high-sensitivity microphone, is subjected to signal processing, is subjected to signal acquisition by a data acquisition card (9), and finally is subjected to data processing and operation by a computer (18) to obtain the concentration of gas to be detected; s4, opening an air outlet air valve (15), and starting a micro air pump (19) to pump the measured methane gas out of the micro multi-path variable-diameter T-shaped photoacoustic cell (12).

Description

Multistage coupling amplification photoacoustic spectrum greenhouse gas measurement system and method Technical Field The invention belongs to the technical field of trace gas measurement, and particularly relates to a multistage coupling amplification photoacoustic spectrum greenhouse gas measurement system and method. Background Currently, high-precision detection technologies of trace gases (such as methane) mainly comprise methods such as an electrochemical gas sensor, a gas-sensitive method, a thermocatalytic method, a gas chromatography method and the like. The detection accuracy of the methods can reach PPM level, but is based on a non-optical detection principle. Compared with the optical detection method, the non-optical detection method has the advantages of narrow dynamic range, long acquisition, sampling and processing time and inapplicability to online real-time detection. The optical method is mainly based on direct absorption spectroscopy, but its detection capability is directly related to the optical path length. Therefore, in practical measurements, to achieve a smaller detection limit, it is often necessary to use a longer optical cavity for the measurement, which also leads to an increase in the gas consumption of the instrument as a whole. The main use of the TDLAS technology is the methane gas detection method using tunable diode laser absorption spectroscopy, but the equipment cost is high and the volume is large. In the PAS-based trace gas detection technology, the detection performance of the system can be effectively improved by enhancing the absorption of the gas to the laser energy, and the system has lower cost and small volume. Today, methane detection technology is in a continuous development and innovation stage, and it is particularly important how to improve sensitivity and reduce cost of a detection system, and meanwhile, higher requirements are also put on portability and integration of the detection system. Current methane detection techniques have been able to achieve very low detection limits, but still require further improvement in detection sensitivity. Most of the current methane detection research is focused on a single direction, and high sensitivity and portability cannot be simultaneously achieved. In order to achieve high sensitivity, some studies have focused on the use of high-precision instruments and complex techniques in order to accurately detect methane content. However, this approach often requires large equipment and specialized operators, and is not well suited for mobile or portable applications. On the other hand, some researches have focused on developing portable methane detection apparatuses to meet the demands of practical applications. These devices are generally small, lightweight, and easy to carry and handle. However, they typically sacrifice a degree of accuracy and sensitivity in order to achieve portability. Accordingly, there is a need for an improved detection system. Disclosure of Invention Aiming at the defects of the prior art, the invention aims to provide a multistage coupling amplification photoacoustic spectrum greenhouse gas measurement system and a multistage coupling amplification photoacoustic spectrum greenhouse gas measurement method, which solve the problems in the prior art. The aim of the invention can be achieved by the following technical scheme: A multi-stage coupling amplification photoacoustic spectrum greenhouse gas measurement system comprises a miniature multi-pass variable-diameter T-shaped photoacoustic cell, a gas distribution system, a DFB laser, a collimating lens, a data acquisition card and a computer, wherein a first reflecting mirror and a second reflecting mirror with an inlet hole are respectively arranged at two side windows of the miniature multi-pass variable-diameter T-shaped photoacoustic cell; The gas distribution system is used for introducing and filling the gas chamber of the miniature multi-pass variable-diameter T-shaped photoacoustic cell with gas to be tested, the DFB laser generates modulated laser, the modulated laser enters the miniature multi-pass variable-diameter T-shaped photoacoustic cell from an incident hole of the first reflecting mirror through the collimating lens and is reflected back and forth between the reflecting mirror and the second reflecting mirror, a plurality of light spots are formed on the mirror surface, the laser is emitted from the incident hole of the first reflecting mirror, a multi-stage coupling amplified photoacoustic signal is generated in the miniature multi-pass variable-diameter T-shaped photoacoustic cell, the photoacoustic signal is received by the high-sensitivity microphone, the signal is acquired by the data acquisition card after the signal is processed, and finally the data processing and the operation are carried out by the computer. The measuring system further comprises a function generator, a phase-locked amplifier, an adder and a laser con