| High concentrations of carbon dioxide can affect the respiratory health of residents,and in severe cases,it can be life-threatening.Monitoring the concentration of carbon dioxide in the air is of great significance for ensuring residents’ respiratory safety and achieving carbon reduction and emission reduction goals.Photoacoustic spectroscopy is a trace gas detection technology based on the photoacoustic effect.It has the advantages of high sensitivity,good selectivity and compact structure with broad application prospects.In this paper,based on photoacoustic spectroscopy technology,carbon dioxide gas detection research is carried out,and the carbon dioxide gas photoacoustic sensor system is built using infrared radiation light source and non-resonant photoacoustic cell.The specific research work and achievements are as follows:Starting from the absorption spectrum theory,the heating and sound generation process of the photoacoustic effect is deeply studied,and the corresponding relationship between the photoacoustic signal and the incident light power,the photoacoustic cell constant,and the gas concentration is established,which lays the foundation for the gas photoacoustic detection.After theoretical research,infrared radiation light sources and non-resonant photoacoustic cells are selected to achieve the design goals of miniaturization and low power consumption,and a non-resonant photoacoustic sensing system architecture is proposed.The photoacoustic cell is the key of the whole sensing system.In this paper,a new non-resonant photoacoustic cell structure is used with description of how to excite the photoacoustic effect and the sound tightness and air transmission ability of the structure.Build a non-resonant gas photoacoustic sensing system model using MATLAB and COMSOL software,simulate the relationship between photoacoustic signal and light source power,modulation frequency,and determine the geometric structure and parameters of the non-resonant photoacoustic cell based on simulation design.Based on the simulation results,a photoacoustic cell and related circuits are developed.EMIRS200 infrared radiation source,ICS-40619 microphone,4.26 um narrowband mid infrared filter,ES662 EPTFE film,and 7265 phase-locked amplifier are selected to build a non-resonant gas photoacoustic sensing experimental platform,and experimental parameters and steps are determined.Based on the photoacoustic experimental platform for detecting carbon dioxide,the relationship between the photoacoustic signal and the power and modulation frequency is first explored.The results show that the photoacoustic signal linearly increases with the increase of the light source power,but decreases with the modulation frequency.Finally,the optimal experimental parameters are determined to be a working voltage of 8.4V and a modulation frequency of 24 Hz for the light source.Measure the photoacoustic signals of different concentrations of carbon dioxide within the range of 0-3000 ppm,complete the calibration of the photoacoustic signal intensity and gas concentration,obtain the quantitative relationship formula of the photoacoustic signal of carbon dioxide concentration,and calculate the detection limit of the non-resonant photoacoustic sensing system to be 96 ppm.Comparing the non-resonant photoacoustic sensing system with commercial NDIR MH-Z16 and photoacoustic SCD40,it is found that the core component volume of the sensor is significantly reduced,achieving the initial miniaturization design goal.However,further improvement and optimization are needed to reduce power consumption,expand the measurement concentration range,and shorten response time. |
