| Trace gas detection is of great significance in life.Photoacoustic spectroscopy detection technology has the characteristics of high sensitivity,high long-term stability,and long service life,which is suitable for application in the field of trace gas detection.Based on the fact that there is little research on the influence factors of photoacoustic spectroscopy gas detection by predecessors,this paper studies the influence factors and mechanism of photoacoustic spectroscopy gas detection systems from theoretical and experimental aspects,focusing on the influence of temperature on the overall system.In this paper,a photoacoustic cell with gas pre-heating channel is designed,and a photoacoustic spectroscopy gas detection system is built.The temperature drift model of photoacoustic cell resonance frequency,quality factor and photoacoustic signal amplitude is theoretically established,and the theory is verified by gas detection experiment,and the mechanism of temperature influence on photoacoustic spectroscopy gas detection is explored.The main work of this dissertation is as follows:1.The basic principles of photoacoustic spectroscopy gas detection were described in detail,including gas absorption theory,photoacoustic signal generation,and detection principles.Through theoretical analysis,the mathematical model of photoacoustic signal and gas concentration was derived.Based on the cylindrical resonant photoacoustic cell,the relationship between the resonance frequency,the quality factor,and the size of the photoacoustic cell was analyzed,and the corresponding mathematical model was established.Based on this model,we designed a photoacoustic cell with an annular gas preheating channel and obtained the sound pressure distribution and resonance frequency of the photoacoustic cell by using COMSOL.2.The influence factors and mechanism of the photoacoustic spectrum gas detection system are studied theoretically,and the influence of temperature and noise on the photoacoustic spectrum gas detection system is analyzed respectively,especially the influence of temperature.The temperature drift models of photoacoustic cell resonance frequency,quality factor and photoacoustic signal amplitude are established respectively,and the influence mechanism of temperature on photoacoustic spectrum gas detection is explored.The noise source of the photoacoustic spectrum gas detection system is studied and the corresponding noise reduction method is proposed3.A photoacoustic spectroscopy gas detection system for carbon dioxide detection was built.Based on this system,a series of experiments were conducted,which validated the theoretical analysis.The calibration function between the concentration of carbon dioxide gas and the amplitude of the photoacoustic signal was obtained by detecting carbon dioxide gas with a concentration of 0 ppm,100 ppm,200 ppm,300 ppm,400 ppm,500 ppm,and 600 ppm with a correlation coefficient of 0.9997.The detection limit of the system is 900ppb.The temperature characteristics of photoacoustic spectroscopy detection were experimentally verified.The frequency response curves of the photoacoustic signal of the same concentration of CO2gas at different temperatures,and the relationship curves between the resonance frequency of the photoacoustic cell and temperature were obtained through five temperature experiments.Finally,the relationship between the amplitude and phase of the photoacoustic signal was experimentally investigated.It was found that the phase at the peak of the photoacoustic signal amplitude was always equal at different temperatures. |
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