Capacitive MEMS transducers for acoustic emission testing of materials and structures

This research focuses on the development and evaluation of capacitive Micro-Electro-Mechanical-Systems (MEMS) transducers for acoustic emission (AE) testing of materials and structures. The MEMS transducers consist of multiple resonant capacitive MEMS transducers in the frequency range of 100 kHz to 1MHz, located on a single 1 cm x 1 cm device. The MEMS transducers are manufactured using the commercial three-layer polysilicon surface micromachining process. Two generations of the MEMS transducers are developed. The results of tests of the first generation transducers lead to the development of the second generation transducers.; A set of simple analytical models are used to estimate the electromechanical and mechanical characteristics of the MEMS transducers. The electromechanical characteristics of the MEMS transducers are determined using a capacitance meter and impedance analyzer. The mechanical characteristics of the MEMS transducers are tested using simulated AE sources. These tests verify the accuracy of the idealized behaviors of the MEMS transducers and simple analytical models experimentally.; The AE tests with simulated acoustic emissions are performed on the first generation transducers in order to show the potential advantages of the MEMS transducers as compared to commercial AE transducers. The second generation transducers are evaluated with both simulated acoustic emission and real damage precipitated AE sources. In the real damage induced AE tests, four welded beam specimens are tested under four-point bending. The advantages of recording output signals of multiple transducers on a small area are shown.; In general, excellent agreement exists between simple analytical models of the MEMS transducers and experimental results. As compared to other currently available approaches, the greater density of transducer placement that is provided with MEMS transducers permits redundant measurement at a point. Redundant measurement at a point increases the accuracy of AE evaluation and the estimate of arrival time, therefore the estimate of wave velocity. An algorithm that applies the cross correlation method to the output signals of the MEMS transducers successfully distinguishes noise signals from AE signals. This research is the first time that capacitive MEMS transducers are designed, fabricated, and used successfully to detect real acoustic emissions.