Gas Sensing Method Based On Sound Velocity Dispersion Decomposition And Relaxation Time

Effective and fast sensing and monitoring of the composition and state of mixed gases has been paid much attention in many different fields.The acoustic sensor has the advantages of high sensitivity,low cost,high real-time,etc.,and because the relaxation process of gas molecules leads to the phenomenon of sound velocity dispersion,so the relaxation characteristics which reflect the gas composition can be obtained through the decomposition of sound velocity spectrum,which makes the gas sensing method based on sound velocity become one of the research hotspots of gas sensing technology.Based on the existing theoretical analysis method of acoustic relaxation,this thesis derives and corrects the expressions of sound velocity and dispersion intensity of sound velocity from the expression of the total effective specific heat capacity of the mixed gases.Combined with the algorithm proposed by this research group to reconstruct the sound velocity spectrum with a limited sound velocity value,it is proved that there is a quantitative relationship between the dispersion intensity of sound velocity obtained by reconstructing the sound velocity spectrum and the corresponding gas composition concentration,and the relaxation time obtained can be used as the basis for qualitative detection of gas composition,according to which a qualitative and quantitative mixed gas blind detection method at a single temperature is proposed.For unknown mixtures,qualitative and quantitative detection of two main relaxation component gases can be achieved by measuring the current temperature softened with the sound velocity value of 5 different sound frequencies.Compared with the existing sound velocity-based gas sensing method,the method proposed in this thesis requires less measurement and eliminates the need for repeated measurements without changing environmental conditions,and is more fault-tolerant and real-time.Then,in order to visualize the gas detection results,a gas imaging method based on the decomposition of sound velocity dispersion is proposed.Inspired by the existing gas imaging methods,a two-dimensional ultrasonic sensor array is designed to apply the above gas sensing method to the qualitative detection and quantitative concentration field reconstruction of the two-dimensional mixture plane.Compared with the existing acoustic relaxation-based gas imaging method,the measurement need of sound intensity attenuation is reduced,the algorithm is less complex and more practical.Finally,in order to verify that the theoretical research results of this thesis can be used for the extraterrestrial planet's atmospheric environment,and to develop the application field of gas sensing method based on the speed of sound,this thesis,taking Titan as an example,uses the measured environmental data brought back by Huygens to predict the change of the atmospheric sound velocity and sound absorption coefficient of Titan with the altitude.The practical application effect of the gas sensing method proposed is further verified by using the sound velocity value at 3 frequencies at different altitudes to reconstruct the concentration of methane with altitude in Titan's atmosphere accuratelyThis thesis perfects the theoretical model of the sound velocity dispersion of the complex relaxation process of mixed gas,and puts forward a qualitative and quantitative gas sensing method with high real-time and practical based on the relaxation time and the dispersion intensity of sound velocity of the mixture gas,which lays the foundation for the design and application of acoustic gas sensors in the future.