Ultrathin, High Sensitivity Polymer-based Capacitive Micromachined Ultrasound Transducers (polyCMUTs) for Acoustic Emission Sensing in Fiber Reinforced Polymers

The arising need to monitor structural health via acoustic emissions (AE) has led to a need for low cost, high sensitivity, and wide bandwidth transducers. For metals, piezoelectric transducers are reliably used, however fiber reinforced polymers present a problem: their acoustic impedance (Z) is significantly lower (~4 MRayl compared to >15 MRayl) meaning a large part of the signal is lost at the interface of sensor and structure. Recently emerged PolyCMUTs devices are distinct, being manufactured using SU-8 with Z ≈3.5 MRayl, implying a minimal loss of signal. Here we present ultrasensitive polyCMUTs and their fabrication process, optimized for AE detection with a wide receiving bandwidth detecting standard pencil lead break (PLB) tests without amplification.