Theory For Gas Composition Sensing Based On Acoustic Velocity Spectrum

Gas detection has wide promising application in many fields,including industrial manufacture,living environment,and how to monitor the gas composition effectively in real time has been a research hotspot.The acoustic-based gas sensing method becomes extremely popular for its advantages such as real-time response,low cost,and high reliability.Acoustic-based gas sensing technology mainly depends on the acoustic attenuation spectrum and the acoustic velocity spectrum.Both the spectrums are formed by the relaxation of gas molecules to detect the components,and contain the composition information of the gaseous medium.The acoustic velocity spectrum is an intuitive manifestation of the sound wave propagation changing with the gas medium information,and therefore,it can be used for gas detection.In this thesis,we propose a fast measurement method that uses a finite number of sound velocity values to reconstruct complete acoustic velocity spectrum.Compared with the existing detection ways of acoustic velocity spectrum,it's unnecessary to measure the acoustic attenuation coefficient,which greatly reduces the measurement error and the device complexity.The correctness and robustness of this method has been verified by Matlab software based on the existing experimental data and theoretical models.At the same time,we find that the coordinates of the inflection point of the acoustic velocity spectrum have obvious information of gas molecular relaxation and then proposes a new method that uses the inflection point of the sound velocity line instead of the complete sound velocity line to detect the gas composition qualitatively and quantitatively.Firstly,the inflection point of the acoustic velocity spectrum can be computed only by the three sound velocity values instead of the complete acoustic velocity spectrum,which has significant advantages of realtime and high-efficiency.Secondly,this detection method introduces ambient temperature as a calibration factor to decrease the detection error,which has the advantages of high accuracy and reliability.Compared with the gas detection method based on the peak point of acoustic absorption spectrum proposed by Hu Yi,the detection method discussed in the thesis effectively avoids the measurement of acoustic attenuation coefficient and simplifies the design and implementation process of gas sensing based on acoustic relaxation theory.Moreover,this method is suitable for multi-gas mixture detection and meets the requirements of high stability and low cost in industrial production,and provides a new idea for the design of acoustic gas sensing technology.