Research On In-vehicle Particle Measurement Method Based On Multi-frequency Surface Acoustic Wave Sensor Array

With the improvement of living standards,people have higher requirements for in-vehicle air quality.Conducting research on in-vehicle particulate matter concentration and particle size distribution measurement methods provides a basis and possibility for developing new invehicle particulate matter measurement methods and improving in-vehicle air quality.Most of the traditional particle measurement methods are large and expensive,which are difficult to be directly used for in-vehicle particle measurement;while the particle measurement methods using resonant sensors have the advantages of small size,simple structure,high sensitivity and low power consumption.Surface acoustic wave sensor(SAW),as a high frequency resonant device,has the advantages of good frequency selectivity,low cost,good process consistency,and easy integration.In this paper,a multi-frequency surface acoustic wave sensor array is used for in-vehicle particle measurement based on frequency perturbation theory and application research.Firstly,the sensitivity of the surface acoustic wave sensor to single particulate matter particle size correlation is investigated.A physical model of the single particle-surface acoustic wave sensor coupled system is developed and simplified to a forced vibration model of the particle-surface acoustic wave sensor coupled system under contact interface excitation using the finite element method.Using the relationship between the contact surface stress integral and displacement,the acoustic impedance imaginary part is derived,from which the frequency perturbation of the sensor by spherical particulate matter with different particle sizes is calculated.The effects of particle size,contact size,shape and material on the particle-acoustic surface wave sensor interaction are investigated.Secondly,based on the sensitivity analysis related to the particle size of a single particle,a coupled perturbation model of particle-size distribution particle-acoustic surface wave sensor is developed to reveal the relationship between particle concentration,particle size distribution and sensor frequency change.The frequency change caused by 1ng PTFE on the surface acoustic wave sensor under different particle size distributions was calculated,and the effects of particle material and device resonant frequency on the sensitivity were analyzed.Experimental measurements of wheat flour and talc particles using the surface acoustic wave sensor were conducted to verify the correctness of the coupling theory:the particulate matter coupled to the surface acoustic wave sensor produces a negative frequency shift in the mass domain;the particulate matter coupled to the surface acoustic wave sensor produces a positive frequency shift in the elastic domain.Experimental measurements of PTFE dust particles with different nominal sizes were conducted using 315 MHz surface acoustic wave sensors to verify the characteristics of surface acoustic wave sensors with different sensitivity to particles under different particle size distributions.Finally,an experimental platform was built to simulate the in-vehicle environment,and an array of acoustic surface wave sensors with resonant frequencies of 315 MHz,433 MHz,and 868 MHz was used to measure aerosols with different particle size distributions in mosquito incense,cigarettes,Arizona A4 powder,and automobile exhaust.The results showed that the particulate matter with different concentrations and particle size distributions were clustered in the principal component space,and the multi-frequency surface acoustic wave sensor array could extract the concentration and particle size distribution information simultaneously.