Dynamic Characteristics of Circular CMUTs with Air-Filled Cavities

Our work deals with the study of the dynamic characteristics of a single circular CMUT transducer under squeeze film damping effect. A simplified analytical approach is developed for parallel plate approximation for the electromechanical behavior and the squeeze film damping. Analytically calculated results demonstrates, that trends of resonant frequency with bias voltage are defined by the ratio of air spring constant to mechanical spring constant. At the same time FEM multiphysics model is built to define the influence of membrane flexibility and venting boundary conditions to the dimensionless viscous and elastic damping forces. FEM study shows the presence of viscous loss in the sealed air-filled cavity and the insensitivity of squeeze film damping forces to the type of lateral venting boundary conditions in high squeeze number region which is typical for CMUT operation. Finally, the experimental dynamic characterization is conducted on CMUT with 67 mu m - 167 mu m radii fabricated utilizing an anodic bonding technology. Experimental data are in a good agreement with the results of multiphysics FEM calculation, which take into account bias voltage, initial plate deflection, radiation loss and squeeze film damping.