Abstract
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.
Highlights
Air-coupled ultrasound has a wide range of potential applications in nondestructive testing,1 air parametric arrays,2 human–computer interaction,3 ultrasonic flow measurement,4 and other fields
In the applications of air parametric arrays, audible sound modulated into an ultrasonic carrier is self-demodulated along a highly directional beam owing to the nonlinearity of air, which generates a highly directional beam of audible sound in air
The basic structure of a Capacitive micromachined ultrasonic transducer (CMUTs) cell is a parallel plate capacitor consisting of a movable upper plate and a fixed lower plate, with a cavity between them
Summary
Air-coupled ultrasound has a wide range of potential applications in nondestructive testing, air parametric arrays, human–computer interaction, ultrasonic flow measurement, and other fields. Piezoelectric ultrasonic transducers have been in widespread use since the 1940s, but have had a limited role in air-coupled ultrasound applications for a number of reasons, in particular the much higher acoustic impedance of the piezoelectric material compared with that of the air. The CMUT with low acoustic impedance can efficiently transfer ultrasound into air and the array design can increase emission energy. All of these characteristics make CMUTs an attractive option for application in air parametric arrays, and the design and investigation of air-coupled CMUT parametric arrays is an important direction of research. Increasing the emission efficiency and improving the directivity of ultrasonic transducers are both significant tasks in the development of air parametric arrays. The fabricated CMUT array is used in preliminary experiments on its application as a parametric array in air
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