Adapting a cMUT transducer to detect acoustic emissions

Abstract

Acoustic emissions are ultrasonic pulses produced in solids when irreversible damage, such as material yielding or crack extension, occurs under mechanical loading. We report on the design, fabrication, and experimental demonstration of a cMUT transducer specifically designed for measurement of acoustic emission events by detecting ultrasonic waves in the 100 kHz to 1 MHz range. The cMUT transducer is intended to replace the commonly used underdamped resonant PZT transducer. In this novel application the ultrasonic energy is coupled to the substrate and the motion of the substrate relative to the supended diaphragm provides an electrical signal. This application requires a very different device design, underdamped and lower in resonant frequency than a cMUT intended for high frequency imaging. We report here the engineering of the quality factor by appropriate spacing of the etch release holes and the fabrication of transducers with multiple resonant frequencies on the same chip. We will also report the detection of actual acoustic emission events and we will compare the cMUT transducers with conventional PZT transducers. Keywords-component; capacitive, MEMS, acoustic emission