Modeling And Analysis Of Capacitive Micromachined Ultrasonic Transducer

In this thesis,firstly,the design principle of capacitive micromachined ultrasonic transducer(CMUT)is analyzed.In addition,the equivalent circuit that is constructed over the Mason model is improved for deriving the formula and theoretical analysis of the relevant parameters of the electrical and mechanical ends of the sensor.Two kinds of CMUT thin films were constructed on the basis of sacrificial layer release process: circular and rectangular membrane.Based on the study of the two kinds of structural parameters,the influence of structural changes on the structural performance is obtained.Based on two parameters that affect the performance of the structure,we analyze the collapse voltage and resonant frequency.Analyzing for circular thin membrane,we obtained actual size parameters of simplified model including the change of radius,thickness,the cavity's gap structure parameters,the changes of those parameters on the resonant frequency and the breakdown voltage,and the initial realization of creating optimization model.Those results provide the basis for further research.We also have designed four kinds of CMUTs' structures with rectangular thin films based on the analysis on building CMUT with sacrificial release method.Through comparing with the four models,we acquired the influence of the various structures including the length,width,ratio of length and width,thickness of membrane and the gap of CMUTs' cavity on the resonant frequency.By using the finite element simulation software,ANSYS,the static analysis,modal analysis on the structure,mechanical and electrical coupled field analysis were carried out.The structural sizes of membrane,resonant frequency and collapse voltage of CMUT can be obtained.Those results provide a theoretical basis for the structural design of the ultrasonic sensor and after processing test.In addition to,the bandwidth of CMUT is studied,and the bandwidth of the sensor is obtained by solving the bandwidth gain of the sensor.However,the calculation requires the sensor gain variable it required: With discussion on the electromechanical conversion ratio of sensor,the capacitor and impedance of membrane,the resonant frequency and the circuit input resistance,the influence of bandwidth on frequency was analyzed.Finally,the future research on hybrid CMUT,which is combined with different sizes of CMUT and has a potential of better image resolution,was proposed.