A Novel Fabrication Process for Thin, Flexible, Backside-accessible Polymer-based CMUTs for Acoustic Emission Sensing

In this work we present an advancement of our previously published work on highly sensitive polymer-based capacitive micromachined transducers (polyCMUTs) for structural health monitoring. This was motivated by the present limitations of today's acoustic emission sensing transducers: most have a large footprint, are made of stiff materials, and need additional matching or protective layers for the typical frontside access for electrical connections. We developed a fabrication process producing thin, backside-accessible, SU-8-based sensitive polyCMUTs. Each polyCMUT element has 500 cells of 90μm diameter on a flexible and optically transparent substrate. The transducers were fabricated, characterized with a laser doppler vibrometer (LDV) showing sensitivity from 40kHz to 3 MHz and tested with a pencil lead break test on a carbon fiber plate resulting in signals from 30 to 100 mv peak to peak.