The Study On Micro-system For Particulate Matter Classification And Concentration Detection

With the continuous and rapid development of our country,the monitoring concentration of particulate matter(PM)in the atmosphere,such as PM2.5/PM1,is increasing.In view of the significant harm of PM2.5/PM1 to the ecological environment and human health,more and more people talk about the air pollution,so that it has been a hot topic in recent years.Considering that the existing monitoring devices are too heavy and complex,which is not convenient for real-time manipulation of individuals and families,this paper proposes a micro-system for airborne particles' classification and concentration detection by using the microfluidics technology and MEMS(Micro-Electro-Mechanical System)sensors.The microfluidics technology can be utilized to separate the PM according to their aerodynamic diameter.Through theoretical calculation and ANSYS simulation,two VIs(Virtual Impactors)are designed to separate PM2.5 and PM1 from aerosol,respectively.By detecting the resonant frequency of MEMS sensor,we can infer the mass,and then the concentration of PM2.5/PM1.This paper first uses QCM(Quartz Crystal Microbalance)sensor to detect PM.It is prove that quality resolution of QCM sensor can reach within 3.647ng.And then a linear relationship(namely the sensitivity)between the frequency shift in the unit time and the concentration of PM is obtained.In order to further improve the sensitivity and reduce the size of MEMS sensor,this paper designs and fabricates a SAW(Surface Acoustic Wave)sensor by silicon micromachining technology.The experimental results show that the sensitivity of the latter increases by 68.4 times.There are 7 chapters in this paper and they are organized as follows:Chapter 1 is about the background of this research and the feasibility of constructing a micro-system for particles' separation and concentration detection.Taking QCM sensor and SAW sensor as examples,the definition,classification and application of MEMS resonators as well as their working principle are detailed introduced.Finally,the research status at home and abroad is classified and summarized,according to the different principle of PM detection.Chapter 2 mainly explains the design,simulation and processing of the VIs.First,the principle of PM separation is introduced,and the primary model of VII for separating PM2.5 is obtained by theoretical calculation.Then,ANSYS software is used to simulate 2D/3D modeling of VI1 and motion trajectory of PM under the DPM(Discrete Phase Model).The final VII structure is completed by changing the shape and size of its flow channels.On the basis of VI1 design,this chapter further designs the VI2,which is used to separate PM1.Chapter 3 briefly illustrates the testing principle and method of QCM sensor,and gets the frequency-impedance curve.Series resonant frequency fsis proved to be reliable.And then the PM separation platform is built,aerosol particles are adhered to the coating surface of the QCM sensor after through VI1.This chapter gets the size distribution of PM in SEM(Scanning Electron Microscope)and the proportion of PM2.5 by MATLAB image processing program.Chapter 4 elaborates the PM2.5 concentration detection experiment based on QCM sensor.After building the PM concentration detection platform,aerosol particles are formed from fine quartz powder with different concentrations in the PM cavity.Under the action of micro-pump,PM2.5 is adhered to the surface of QCM sensor via the classification of VI1.The frequency shift of QCM sensor is detected by network analyzer to infer PM2.5 concentration.Finally,the sensitivity of the QCM sensor is measured.Chapter 5 presents a new type of SAW sensor.Forked finger transducer in the SAW sensor is fabricated to reduce the acoustic diffraction and parasitic frequency response.Piezoelectric substrate is combined aluminum nitride with silicon material so as to improve the temperature and chemical stability.Then the MEMS processing technology of SAW sensor is introduced,and the finished production is tested.Chapter 6 introduces the PM1 concentration detection experiment based on SAW sensor.Firstly,PM concentration detection platform is set up.Aerosol particles are deposited or adhered to the surface of the SAW sensor via the classification of VI2.The frequency shift is detected by network analyzer to infer PM1 concentration.Finally,the sensitivity of the SAW sensor is also measured.Chapter 7 summarizes the whole research as well as its scientific contributions.Future work and improvement is also presented.