FEM simulation and measurement validation of a cMUT cell

This paper presents Finite Element Modeling (FEM) simulation and experimental results of the acoustic and mechanical behavior of an isolated cMUT cell. cMUT cells fabricated in the SiGeMEMS technology of imec are used as test vehicles. Dynamic characteristics of a cMUT cell actuated by a pulse superimposed on a DC bias, such as resonance frequency, Q-factor and transient displacement, are studied using ANSYS FEM and Polytec vibrometer measurements. A good agreement is achieved between the FEM simulation results and optical measurements. The Rayleigh integral method is used to construct the spatial pressure field based on the transducer surface information obtained both from ANSYS and the optical measurements. The results are compared with hydrophone measurements, and good agreements are achieved. Acoustic measurements on a typical cMUT cell (measuring ~60μm on the side) in a fluorinert medium (FC-84) show a 7MHz center frequency, ~100% -6dB fractional bandwidth (FBW) and several kilo Pascal peak-to-peak pressure at millimeters scale. Our method provides a clear methodology to accurately predict the transient spatial pressure field of a cMUT cell, especially in the far field region, with little time cost.

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