A MEMS transducer for detection of acoustic emission events

Acoustic emissions are ultrasonic pulses produced in solids when irreversible damage occurs under mechanical loading. We report on the design and testing of a MEMS device, adapted from cMUT technology, to detect acoustic emissions. The device is fabricated in a surface-machined MEMS process and consists of diaphragms supported by springs above a plate. When a DC bias voltage is applied, vibration of the spring-supported diaphragm causes a time-varying current. The MEMS device contains seven independent transducers with resonant frequencies in the range of 100 kHz to 1 MHz. The availability of multiple signals allows for redundant sensing and may facilitate distinction of true acoustic emissions from other events. We report the detection of actual acoustic emission events in structural testing, comparing the performance of the MEMS device with a conventional PZT acoustic emission transducer. In the test, a MEMS device and a conventional transducer were attached to a steel beam specimen which was loaded to failure. Strong acoustic emission events were simultaneously detected by both types of transducers