Experimental study of acoustic coupling in CMUT arrays by optical interferometry

A major mechanism of cross-coupling in capacitive micromachined ultrasonic transducer (CMUT) arrays in immersion operation is represented by the acoustic interactions among the membranes. In this work, acoustic interactions are investigated by means of optical displacement measurements. Experiments are conducted on a variety of CMUTs, with different size and number of elements, using both air and liquids as coupling mediums. In past investigations, Stoneley-type interface waves propagating along the surface of a CMUT array have been identified as an important source of cross-coupling. Indeed, the experimental results herein reported indicate that mutual acoustic coupling through the liquid is mainly responsible for setting the membranes of coupled elements into motion.