Electrical impedace matching of CMUT cells

Abstract

Capacitive micromachined ultrasonic transducers (CMUTs) have admirable performance that make them suitable for use in ultrasound imaging and therapeutic applications. Maximizing acoustic power output from CMUTs is of major importance to ensure competitive signal-to-noise ratio. In this paper, ADS validated models were used to predict device performance before and after using impedance matching networks. Electrical impedance matching of the large signal models of the CMUT cells were studied in detail. Membrane velocity and acoustic pressure of a single 3MHz CMUT cell, a 2 by 10 linear CMUT array and 6 by 6 CMUT square array were measured and compared with and without matching networks. For a given bias voltage, we found the maximum possible AC drive-level we could apply without collapsing the membrane, then found the mean membrane velocity at this signal drive-level in the cases where a matching network was present or absent. The results show remarkable improvements in output acoustic pressure which can be useful for some imaging and especially ultrasound therapeutic applications. The scattering parameters of a 5 by 100 linear CMUT array were measured using a vector network analyzer. Different kinds of impedance matching networks were designed to transfer more power to the arrays. Experiments show admirable improvements and have a good agreement with simulation results.