Design of a hexagonal air-coupled capacitive micromachined ultrasonic transducer for air parametric array

An air parametric array can generate a highly directional beam of audible sound in air, which has a wide range of applications in targeted audio delivery. Capacitive micromachined ultrasonic transducer (CMUTs) have great potential for air-coupled applications, mainly because of their low acoustic impedance. In this study, an air-coupled CMUT array is designed as an air parametric array. A hexagonal array is proposed to improve the directivity of the sound generated. A finite element model of the CMUT is established in COMSOL software to facilitate the choice of appropriate structural parameters of the CMUT cell. The CMUT array is then fabricated by a wafer bonding process with high consistency. The performances of the CMUT are tested to verify the accuracy of the finite element analysis. By optimizing the component parameters of the bias-T circuit used for driving the CMUT, DC and AC voltages can be effectively applied to the top and bottom electrodes of the CMUT to provide efficient ultrasound transmission. Finally, the prepared hexagonal array is successfully used to conduct preliminary experiments on its application as an air parametric array.