An energetic definition of the electromechanical coupling coefficient for CMUTs

The most important property of an electromechanical transducer is its ability to convert electrical energy into mechanical energy and vice versa. This energy conversion is fully characterized by the electromechanical coupling coefficient k. In this paper we introduce a new method for the computation of this parameter for capacitive micromachined ultrasonic transducers (CMUTs), in particular we apply to a single cell the method previously proposed for piezoelectric elements and based on energetic considerations. By means of a distributed analytical model, the k factor is evaluated in dynamic situations as the square root of the ratio between the converted mechanical energy and the total energy involved in a transformation cycle. The obtained quantity depends on the transducer bias voltage and increases with it.