Characterization of MEMS transducer performance using near-field scanning interferometry

Sophisticated ultrasonic transducer microarrays based on micro-electro-mechanical-systems (MEMS) technologies are quickly becoming a reality. A current challenge for many researchers is characterizing the dynamic performance of these and other micro-mechanical devices. In this work, the performance characteristics of a MEMS ultrasonic transducer array were successfully measured using a scanning heterodyne interferometer system. The dynamic response of the entire transducer array was measured, and the results were compared with theoretical predictions. Individual elements were found to vibrate with Bessel-like displacement patterns, and they were resonant at approximately 4 MHz. The full array showed variations in peak out-of-plane displacement levels across the device of 16%, and isolated elements that were dramatically overresponsive and under-responsive. The measured variations across the array may have an undesirable impact on the performance of the transducer and its radiated field.