CN-121207878-B - Photoacoustic gas sensor adopting microphone array

Abstract

The invention belongs to the field of industrial gas detection, discloses a photoacoustic gas sensor adopting a microphone array, and designs a T-Helmholtz photoacoustic cell based on the microphone array. TDHMA photoacoustic cells are added with a plurality of resonant cavities to form a multi-T-shaped structure on the basis of the traditional Helmholtz photoacoustic cells. A MEMS microphone is mounted at the end of each resonator to detect photoacoustic signals. And respectively superposing a plurality of in-phase signals and a plurality of anti-phase signals generated by TDHMA through an adder circuit, and then subtracting the two superposed PA signals. Compared with the traditional Helmholtz photoacoustic cell, the TDHMA photoacoustic cell enables sound pressure to be concentrated at the tail end of the resonant tube, can generate larger photoacoustic signals, and has stronger noise suppression capability.

Inventors

• LI YAFEI
• HUANG CHEN
• Deng Chaobei
• Guan Yanxiong
• DENG WANLING
• HUANG JUNKAI
• GUO TUAN

Assignees

• 暨南大学

Dates

Publication Date

20260505

Application Date

20251113

Claims (5)

1. 1. The photoacoustic gas sensor adopting the microphone array is characterized by comprising a laser, a signal generator, a microphone array T-Helmholtz photoacoustic cell, an addition circuit, a lock-in amplifier, a data acquisition card, a laser driver and a Labview upper computer; The signal generator is used for generating a driving signal and a reference signal, the laser driver drives the laser according to the driving signal, the generated laser beam is perpendicular to the window sheet and enters the buffer cavity of the T-shaped Helmholtz photoacoustic cell of the microphone array, the reference signal is sent into the phase-locked amplifier for frequency locking, and the obtained second harmonic signal is used for measuring the gas concentration; the laser device is used for generating a laser beam to be emitted into the photoacoustic cell for gas detection; The MEMS microphone is arranged at the tail end of a resonant cavity of the T-shaped Helmholtz photoacoustic cell of the microphone array and is used for detecting photoacoustic signals generated by periodical shrinkage and expansion after gas molecules absorb light energy, and the received photoacoustic signals are sent into a phase-locked amplifier through an adder circuit to extract 2f signals related to gas concentration; The data acquisition card is used for transmitting a 2f signal related to the gas concentration to the Labview upper computer, and carrying out real-time dynamic monitoring on the gas concentration.
2. 2. The sensor of claim 1, wherein the T-shaped helmholtz photoacoustic cells of the microphone array generate two opposite-phase photoacoustic signals through a helmholtz structure, and the sound pressure is concentrated at the tail ends of the resonant cavities by combining the T-shaped photoacoustic cells, 4 resonant cavities are additionally arranged on the wall of each buffer cavity, and MEMS microphones are respectively arranged at the tail ends of the resonant cavities.
3. 3. A sensor according to claim 2, wherein in the differential output mode of the T-helmholtz photo acoustic cell of the microphone array, photo acoustic signals of opposite phases are generated, photo acoustic signals of in-phase are generated at the microphones 1-4, photo acoustic signals of opposite phases are generated at the microphones 5-8, the in-phase signals and the opposite phase signals are added by an adding circuit, the added differential signals are subtracted again, the photo acoustic signal amplitude is increased after the signal subtraction, and the noise signals of in-phase are reduced after the subtraction, thereby obtaining photo acoustic signal amplitude meeting preset requirements, the generated noise components are in-phase, and the noise signals collected at the microphones 1-4 and the microphones 5-8 are in-phase and equal.
4. 4. A sensor according to claim 3, wherein the in-phase photoacoustic signal is generated at the microphones 1 to 4, and the opposite-phase photoacoustic signal is generated at the microphones 5 to 8, and the in-phase photoacoustic signal and the opposite-phase photoacoustic signal are added by an adding circuit, and the added differential signals are subtracted, thereby obtaining the photoacoustic signal amplitude satisfying the preset requirement by: ; Where x 1 、x 2 、x 3 、x 4 、x 5 、x 6 、x 7 、x 8 is the acoustic signal and x output1 and x output2 are the output signals.
5. 5. The sensor of claim 4, wherein the method of calculating noise signals for the microphone array comprises: ; where N output2 represents the noise added value of the output signal x output2 of microphone 5-microphone 8 and N output1 represents the added value of the noise of the output signal x output1 of microphone 1-4.

Description

Photoacoustic gas sensor adopting microphone array Technical Field The invention belongs to the field of industrial gas detection, and particularly relates to a photoacoustic gas sensor adopting a microphone array. Background Methane (CH 4) and acetylene (C 2H2) are two common hydrocarbon gases, which have important industrial application value, but also present significant safety hazards and environmental risks. Methane is the main component of natural gas, and is widely used in the fields of energy production and chemical industry, but the high combustibility of the methane can cause explosion accidents, acetylene is commonly used for metal welding and cutting, but the instability and toxicity of the acetylene can pose a threat to human health. A small fraction of these two gases originate from natural processes such as wetland microbiological activity and plant metabolism, but most of the emissions come from human activities including fossil fuel exploitation, industrial leakage and chemical production. Methane and acetylene may not only cause fires and explosions, but also exacerbate the greenhouse effect (methane is a powerful greenhouse gas) or cause acute poisoning (acetylene is narcotic and choking). Therefore, the development of the high-sensitivity and high-selectivity gas sensor capable of simultaneously detecting methane and acetylene has important significance for industrial safety monitoring, environmental pollution prevention and control and occupational health protection. The development of a high-sensitivity and high-selectivity gas sensor capable of simultaneously detecting methane and acetylene has important significance for industrial safety monitoring, environmental pollution prevention and control and occupational health protection. Among the common gas detection methods, the infrared absorption spectrum gas detection technology has better selectivity, sensitivity and long-term stability compared with the traditional electrochemical, catalytic combustion and semiconductor gas detection technologies. Common infrared absorption spectroscopy gas detection techniques include Direct Absorption Spectroscopy (DAS), tunable Diode Laser Absorption Spectroscopy (TDLAS), off-axis integrated cavity output spectroscopy (OA-ICOS), and photoacoustic spectroscopy (PAS). Regarding the present design of Helmholtz sensors using photoacoustic spectroscopy, ma et al fabricated Helmholtz cells with a volume of only 1/16 of that of the conventional H-type photoacoustic cell, and the experimental results showed that the detection limit of hydrogen sulfide (H 2 S) was 460 ppb. Wang et al designed a helmholtz photoacoustic cell with a volume of 0.5 mL that employed a double junction tube structure to suppress gas flow noise and achieve a C 2H2 detection limit of 300 ppb. However, helmholtz photoacoustic cells suffer from uneven sound pressure distribution at the resonant frequency, resulting in photoacoustic signal attenuation and insufficient noise suppression capability. Feng et al developed a highly sensitive and miniaturized T-type photoacoustic gas sensor that effectively reduced flow noise and amplified PA signals by optimizing the geometric refinement of the transition between the buffer and resonant cavities, achieving the C 2H2 detection limit of 278 ppb. However, the single buffer cavity design of the T-cell is difficult to completely isolate low frequency vibrational disturbances, yet still susceptible to ambient noise, thereby reducing the signal-to-noise ratio (SNR). Disclosure of Invention In order to solve the problem that the prior art cannot accurately realize gas detection which is easy to break away from the influence of environmental noise, has concentrated sound pressure distribution and improves signal to noise ratio (SNR), the invention provides a photoacoustic gas sensor adopting a microphone array, which can realize methane and acetylene gas detection which is easy to break away from the influence of environmental noise, has concentrated sound pressure distribution and improves the signal to noise ratio. In order to achieve the above object, the present invention provides the following solutions: a photoacoustic gas sensor adopting a microphone array comprises a laser, a signal generator, a microphone array T-Helmholtz photoacoustic cell, an addition circuit, a phase-locked amplifier, a data acquisition card, a laser driver and a Labview upper computer, wherein the laser is connected with the signal generator; The signal generator is used for generating a driving signal and a reference signal, the laser driver drives the laser according to the driving signal, the generated laser beam is perpendicular to the window sheet and enters the buffer cavity of the T-shaped Helmholtz photoacoustic cell of the microphone array, the reference signal is sent into the phase-locked amplifier for frequency locking, and the obtained second harmonic signal is used for measuring the gas concentration; the