Technical Papers and Presentations

Acoustic emissions generated by active defects in structures, like bridges, aircraft, and pipelines, play a crucial role in detecting flaws in their structural integrity by non-destructive evaluation techniques. Commercially used acoustic emission (AE) sensors are made of piezoelectric materials and operate in resonance mode. The material and geometric properties of the resonating structure determine the resonance frequency of the sensor. These AE sensors are bulky and expensive. Methods to miniaturize the AE sensors using micromachining techniques have been widely reported. These techniques reduce the overall footprint of the sensor and make them cost-effective due to the batch production capability of MEMS fabrication processes. The MEMS-based AE sensor must detect a wide range of frequencies to identify the acoustic emission sources and associated defects correctly.
In our work, we have utilized an 8-electrode configuration on a single membrane that takes advantage of several transverse modes of vibration of a circular membrane, which could be used to detect multiple frequencies in an AE event. The electrodes are arranged in a way to maximize the charge produced by the piezoelectric layer by the localized displacement of the structure due to resonances at frequencies of 64.5 kHz, 134.5 kHz, and 220.5 kHz. The spread of frequencies in this spectrum is important for its utilization in the nondestructive testing of concrete. The simulation consists of a model of a circular membrane with piezoelectric layers arranged in the geometry of the electrodes. We have incorporated solid mechanics from the structural mechanics module and electrostatics from the AC/DC module for the FE analysis. With the piezoelectric effect in multiphysics enabled, we could simulate the voltage generated by the piezoelectric layer due to a body load over a range of frequencies, demonstrating the ability of our single membrane sensing mechanism.