Representation of CMUT-based isolation transformer by means of an electrical two-port network

It has been shown in previous works that Capacitive Micromachined Ultrasonic Transducers (CMUT) could be an attractive alternative for the development of galvanically isolated transformers. These devices are ultrasonic transformers made of two CMUT arrays placed on each side of a silicon substrate. The resonance mode associated with the thickness of the substrate is used to transmit the acoustic signal from the emitter to the receiver. A thick silicon oxide layer buried in the substrate ensures a high level of electrical isolation. The present work aims to develop a theoretical method to implement the electrical equivalent two-port network of the transformer. The determination of the transfer matrix elements, is detailed both theoretically and experimentally. An example of application of the equivalent network is given: the optimization of the power efficiency by tuning the electrical load conditions on the input and output port of the transformer.