Finite Element Analysis Of Capacitive Micromachined Ultrasonic Transducer And Deformation Research Of Its Membrane

Ultrasonic technology has been widely used in such applications as medical imaging and non-destructive testing. As core devices of all ultrasonic applications, ultrasonic sensors have always been a research focus. Capacitive micromachined ultrasonic transducer(CMUT), which overcomes the impedance mismatch defect of the traditional piezoelectric ultrasonic transducer, has great prospect and research value due to its advantages of wide bandwidth, high sensitivity and ease of integration.The most important component of CMUT is membrane, the deflection of which can be used not only to calculate the change in capacitance, but also to analyze the stability of the transducer. Therefore, the membrane deformation is an essential factor to be considered in the CMUT design process. Therefore, this paper conducts research mainly on deformation of CMUT membranes(including rectangular membranes and elliptical membranes) under electrostatic force.Firstly, this paper establishes a simplified 3D finite element model of CMUT based on its structural characteristics in finite element analysis(FEA) software ANSYS 15.0. For purpose of improving computational efficiency, only 1/4 of CMUT is analyzed in the model. Through static analysis, the effectiveness of the finite element model and the analytic method is verified by comparing collapse voltages with an existing research. For better simulation of practical situation, we further improve the finite element model by taking account of the top electrode’s effect on the membrane. And modal analysis is also conducted to calculate the natural vibration frequency of CMUT.Secondly, the FEA results are employed to study the influences of DC bias voltages and membrane geometry dimensions on the membrane deformation. Some basic functions are selected and proposed to describe the general trends of the deformations. On this basis, we first propose mathematical deformation models for CMUTs’ rectangular and elliptical membranes, respectively. And a two-dimension function is also proposed for the models to analyze the effects of the membrane geometry dimensions.Finally, with the new deflection shape models, we calculate the capacitance values of CMUTs by numerical integration method and draw some deformation surfaces of membranes for reference of membrane design. In addition, in both small deflection and large deflection cases, the accuracies of the new deformation models are verified in two aspects: similarity of deformed curves and error in capacitance values. To be more specific, in a group of random tests, compared with FEA results, the calculated capacitance values have a maximum deviation of 0.436% for the rectangular membranes and a maximum deviation of 2.920% for the elliptical ones.