Research On Modeling And Simulation Technology Of Capacitive Micromechanical Ultrasonic Transducer

As a high technology,ultrasonic imaging technology has been widely used in many fields,such as industry,medicine,national defense and so on.Ultrasonic transducer is the core device in ultrasonic imaging system.Its performance directly affects the effect of ultrasonic imaging.The capacitive micromechanical ultrasonic transducer(CMUT)fabricated on the basis of MEMS process has the characteristics of high frequency bandwidth,high electromechanical conversion efficiency,high sensitivity,easy compatibility with IC process,easy matching with working medium impedance,and so on.Therefore,it has a broad application prospect in the field of industrial nondestructive testing,medical ultrasonic diagnosis and treatment,etc.CMUT modeling and simulation is not only the foundation of optimizing CMUT structure parameters,but also the premise to realize its fabrication.Therefore,the research on modeling and simulation of CMUT in this thesis is of great value in scientific research.The main contents of this thesis are as follows:(1)The theoretical model of CMUT is studied,and the characteristic parameters of CMUT,such as vibration displacement,natural frequency,collapse voltage,mechanical impedance and bandwidth,are obtained.In addition,the acoustic radiation impedance of CMUT is briefly introduced,which lays a foundation for the subsequent establishment of the equivalent circuit model.(2)The finite element model of CMUT cell is constructed in COMSOL Multiphysics(a finite element analysis software),and the static analysis,modal analysis,harmonic response analysis and transient analysis are carried out.As a consequence,the collapse voltage,characteristic frequency and other important parameters of CMUT are obtained.(3)The equivalent circuit models of CMUT cell are established,including the clarge signal equivalent circuit model and the small signal equivalent circuit model.The equivalent circuit of CMUT cell is established in Advanced Design System(ADS).The harmonic balance simulation of large signal equivalent circuit and the transient simulation of small signal equivalent circuit are carried out.Based on the equivalent circuit models of CMUT cell,the equivalent circuit model of CMUT is established.The effect of the size,number and spacing of cells on the characteristic frequency of CMUT is analyzed.The above analysis results provide an important theoretical reference for optimizing the structural parameters of CMUT.