Research On High Sensitive Photoacoustic Spectrum Detection Technology And System

With the development of science and technology and the needs of social progress,the application of dissolved gas detection in power system transformer oil and military toxic gas detection place higher requirements on traditional gas detection technology.Fast,instant,small volume,highly sensitive,multi-component and trace detection has become a development trend of gas detection system.Photoacoustic spectroscopy(PAS)is a traditional high-sensitivity optical detection technology.This method is based on the photoacoustic effect of the sample to reflect the characteristics of the sample,such as sample concentration and composition.The detection sensitivity of the system mainly depends on the detection sensitivity of the acoustic sensor and the ability to suppress the main noise of the system.Early photoacoustic spectroscopy systems mainly used the membrane microphone to detect photoacoustic signal.The electrical noise and non-linearity of the signals caused the overall detection sensitivity of the system to be limited.Recently,some scholars have proposed a new type of optical cantilever microphone.The application of this acoustic sensor has improved the sensitivity of the photoacoustic spectrum detection system,but the noise suppression ability of the cantilever microphone has rarely been discussed.Based on this,we propose a highly sensitive photoacoustic spectrum detection system based on a differential torsion beam combined with a Helmholtz photoacoustic cell.The main work of this article will be introduced from the following sections:(1)Firstly the theoretical part of photoacoustic spectrum detection technology is deeply analyzed,including the principle of sound signal generation of photoacoustic spectrum detection technology,and the basic theory of traditional Helmholtz photoacoustic cell and the differential torsion beam.(2)Then,through Comsol simulation software,the method of finite element analysis was used to combine the thermophysical viscous sound field,the pressure sound field,and the solid physical field coupling multiple physical fields to simulate the Helmholtz photoacoustic cell and the acoustic sensor of differential torsional beam.In order to reduce low-frequency noise,through the design of geometric structure resonant frequencies of the cell and the sensor are above 1kHz.Firstly an experiment was carried out to compare the characteristics of the processed Helmholtz photoacoustic cell with the simulation results,which proved the reliability of the finite element simulation software.Then,the acoustic sensors are designed by software simulation and processed by laser cutting system.Finally,an experiment was performed to compare the noise suppression capability of the newly proposed torsional beam acoustic sensor with the noise suppression capability of the most sensitive cantilever acoustic sensor.The result show that compared to the cantilever beam sensor,the noise suppression capability of the differential torsion beam acoustic sensor improves an order of magnitude.(3)The last part is the construction of the gas detection system.First,the type of gas to be measured and the characteristic absorption spectrum are selected.The method of dual beam including opposite phase is used to eliminate coherent noise,resonance of Helmholtz photoacoustic cell and torsion beam acoustic sensor is used to improve the Q value of the system,and the excellent ability of the torsion beam acoustic sensor to suppress background noise.Combined with the DFB light source and signal processing parts,a highly sensitive photoacoustic spectrum detection system is used to detect the sample.This method will greatly improve the detection sensitivity and signal-to-noise ratio of the system.