5G-1 Two Approaches to Electronically Scanned 3D Imaging Using cMUTs

Capacitive micromachined ultrasonic transducers (cMUTs) introduce new degrees of freedom in transducer design. For example, it is easy to make elements of any size, and electronics may be integrated directly under the transducer element. These characteristics derive from lithographic manufacturing on a silicon substrate, and the use of a low-temperature surface micromachining process. They are particularly helpful in creating 2D arrays for electronically scanned volume imaging. This paper describes two contrasting ways to achieve volume data acquisition. In bias voltage scanning, we create a Fresnel elevation focus using a crossed electrode design with traditional azimuth beam formation. Then using the bias voltage dependence of k_T in a cMUT, N² element connections can be reduced to 2N. Such a scheme is especially useful in high frequency linear scanning, where N can exceed 200 elements. Measurements and images from a prototype probe are presented. We also describe a method to achieve fully sampled 2D receive apertures with autonomous elements using monolithically integrated electronics. This achieves spatial Nyquist sampling in both array dimensions, with arbitrary element delay and amplitude control. It allows much more of the information in the field returning to the probe to be retrieved by the imager, causing improvements in image quality and diagnostic confidence