Research On Trace Gas Detection Technology Based On Umbrella-shaped Resonant Photoacoustic Cel

With the development of times and the pursuit of high quality of life,trace gas monitoring has gradually become an important part of production life.Photoacoustic spectroscopy has become one of the common methods for trace gas detection due to its high sensitivity,fast response time and zero background noise.The optimization of photoacoustic cell,which is one of the cores of photoacoustic spectroscopy,has also become a hot topic of research.Miniaturization,portability,and high sensitivity are all trends in the optimization of photoacoustic cells.In this paper,a new umbrella resonant photoacoustic cell is proposed.Compared with the conventional H-shaped photoacoustic cell,this new resonant photoacoustic cell has a higher resonant frequency,higher acoustic pressure and smaller size.The resonant frequency of the umbrella resonant photoacoustic cell and the acoustic pressure distribution inside the photoacoustic cell were simulated and analyzed by COMSOL Multiphysics software.The optimal geometric parameters of the photoacoustic cell were determined by changing the diameter and length of the two cylindrical cavities and the bottom diameter and bottom angle of the conical cavity,respectively.The optimal geometric parameters of the photoacoustic cell were determined by considering the size,the resonant frequency,the maximum sound pressure magnitude and the sound pressure distribution.The photoacoustic spectroscopy measurement system was built on this basis.The DFB laser with a central wavelength of 1567 nm was used as the excitation source to measure different concentrations of CO gas,and the signal-to-noise ratio of the system was 7.575 with a minimum detection limit of 1.3%.Since the absorption coefficient of CO is too small,the laser power used in the experiment is weak,then the CH₄gas with a larger absorption coefficient was measured.The measured data were denoised to obtain a signal-to-noise ratio of 223.8 and the minimum detection line of 5.36 ppm.The loss of sound pressure amplitude in the photoacoustic cell was analyzed by the surface finish of the cell.The relationship between CH₄concentration and photoacoustic signal was analyzed based on the principle of Helmholtz muffler and Rayleigh scattering.And it is analyzed that the performance of the system will be improved after optimizing the surface finish of the photoacoustic cell,theoretically.