Transmit optimization of CMUTs in non-collapse mode using a transient array model

A transient transmit model has been developed to investigate and optimize output pressure characteristics of a CMUT array element in non-collapse mode. The model uses SIMULINK to calculate transient output pressure from a CMUT array element given the input voltage waveform. The model has a nonlinear block for electrostatic actuation, and two linear blocks for force to membrane displacement and force to pressure calculations. Force to displacement transfer functions are obtained using the boundary element method which accounts for membrane dynamics including acoustic cross coupling in the array and provides surface velocity distribution for pressure calculation more efficiently as compared to FEA. Using the model, the transient transmitted pressure can be simulated for various pulse amplitude and DC bias configurations for CMUT optimization and phased array operation. The model is verified on a 2 by 2 CMUT array which is simulated both with transient FEA and the SIMULINK model. This type of model would be useful for designing a CMUT element optimized for maximum output pressure given input signal constraints and a desired frequency response. As an example, the optimal pulse width and DC bias to maximize the output pressure of a CMUT-on-CMOS dual-ring array element are calculated for given device geometry and constrained drive pulse amplitude of 25 V.