Fem Modelling and Characterization of Ultrasonic Flextensional Transducers

Abstract

This work describes the finite element modelling and characterization of ultrasonic flextensional transducer arrays. Flexural acoustic transducers can be piezoelectrically actuated plates or capacitive devices based on the electrostatic attraction between a moving electrode and a substrate. Due to the limited miniaturization allowed by the piezoceramic fabrication process, piezoelectric flexural devices based on bulk ceramics are able to work in the low-frequency ultrasonic range. Capacitive flexural devices, instead, can take advantage of the Silicon micromachining techniques to be fabricated to reach higher frequencies. Capacitive Micromachined Ultrasonic Transducers (CMUTs) are MEMS devices consisting of miniaturized metallized membranes, forced into flexural vibration by an electric signal during transmission, and vice versa generating a voltage signal when actuated by an incident acoustic signal. Due to their low acoustic impedance, CMUT arrays have given excellent results in ultrasound imaging applications. The most recent frontier of ultrasound imaging is real-time volumetric imaging. 3D images have been originally obtained by means of linear phased arrays mechanically titled along the elevation plane. More complex structures like 2D arrays allow electronic beam steering and dynamic focusing in both azimuthal and elevation planes, thus achieving better performance. In order to increase the achievable frame rate, though, part of the front-end transceive and beamforming operations must be performed in probe. Therefore, 2D arrays should be small-sized and easily interfaced with the front end. Nevertheless, 2D arrays with good radiation characteristics require wide apertures with a small pitch between elements, therefore a great number of elements and many channels to wire and control individually. To overcome these issues, much attention is being focused on the design of sparse arrays, which try to achieve comparable performance by counting a lower element number. ... [edited by Author]