Optimization Of Photoacoustic Cell In Photoacoustic Spectroscopy Methane Gas Detection System

The monitoring of methane gas is essential to daily life,industrial production and safety.Photoacoustic spectroscopy technology is a detection technology that inversely obtains the concentration of the substance to be measured by measuring the amplitude of the acoustic wave produced by the photoacoustic effect.This technology has the advantages of high sensitivity,good selectivity and high stability,continuous real-time monitoring,and no consumption of gas samples,and it is widely used in the field of gas detection.First of all,because the geometric structure of the photoacoustic cell directly affects the detection sensitivity of the system,the article conducts a simulation study on the geometric structure of the cylindrical photoacoustic cell to determine its optimal geometric structure parameters.And on this basis,the geometric structure of the photoacoustic pool is optimized through modeling analysis to achieve the purpose of reducing airflow noise interference.Secondly,a narrow-band low-pass filter is designed.Through simulation,the signal can be amplified and the detection sensitivity can be improved.In this paper,a methane gas concentration detection system is established based on a new optimized photoacoustic cell and a narrow-band low-pass filter,combined with wavelength modulation and second harmonic detection technology,which greatly improves the detection sensitivity of the system.First,based on the principle of photoacoustic spectroscopy detection,a detailed analysis of the gas molecule infrared absorption,incident light modulation,thermal energy generation,acoustic wave excitation,and second harmonic detection in the signal extraction process is carried out.Secondly,the structure and function of the photoacoustic cell,the core component of the photoacoustic spectroscopy detection system,is studied.Based on the cylindrical photoacoustic cell,the relationship between the structure,working mode and photoacoustic signal of the photoacoustic cell,as well as the relationship between the geometrical size of the photoacoustic cell and the resonance frequency,quality factor and cell constant is analyzed with the help of MATLAB software.The finite element analysis software COMSOL Multiphysics was used to establish a photoacoustic cell model,and the sound pressure distribution in the cell was analyzed by adjusting the cavity radius,resonant cavity length,buffer cavity radius,and buffer cavity length to find the optimal size.Combining actual processing and experimental conditions,it is finally determined that the resonant cavity radius is 3mm,the resonant cavity length is120 mm,the buffer cavity radius is 35 mm,and the buffer cavity length is 60 mm.Based on this,a photoacoustic cell with rounded corners connecting the buffer cavity and the resonant cavity is proposed.Through COMSOL Multiphysics modeling and simulation,a higher cell constant and quality factor are obtained,thereby improving the detection sensitivity of the system.Then,this article proposes a narrow-band low-pass filter,which is composed of an integrating comb filter,a half-band filter and a shaping filter.This filter can effectively filter out the noise in the weak signal.On this basis,MATLAB software is used to realize the phase-locked amplification function,and simulates the simulation signal extraction process,which can obtain better detection results.Finally,a methane gas detection experiment system was built to detect the performance parameters of the photoacoustic cell,and the influence of temperature,pressure,buffer gas types on the photoacoustic signal was analyzed,and the detection sensitivity of the system was 0.87 ppm.