Preliminary Demonstration of Pulse-Echo Imaging With a Long Monolithic Flexible CMUT Array

Abstract

Conformal ultrasound imaging using large-area transducer arrays is an emerging technology with significant potential for real-time, continuous, functional, and health monitoring applications. This study addresses the challenge of fabricating such transducer arrays by presenting the development and preliminary imaging performance of a monolithic flexible capacitive micromachined ultrasonic transducer (CMUT) array—the longest reported to date. A 128-element, 91 mm long flexible array was designed and fabricated using a lithography process, with SU-8 CMUT structures on a bendable polyimide substrate. The array was then packaged by mounting it onto a flexible printed circuit board and coated with a thin polydimethylsiloxane (PDMS) layer for in vivo testing. Electrical impedance measurements confirmed the full functionality of all transducer elements, with an average center resonant frequency of 5.84 MHz (SD: 0.14 MHz). Pulse-echo imaging experiments demonstrated the array’s capability to detect specular reflections and resolve fine features under various curvatures. In vivo scans revealed outlines of a finger and superficial tissues in the forearm. Despite the limitations associated with the lack of custom front-end electronics and low signal-to-noise ratio beamforming strategies, this work demonstrates the feasibility of manufacturing a flexible CMUT array suitable for large-area conformal sonography.