MEMS-on-fiber sensor combining silicon diaphragm and supporting beams for on-line partial discharges monitoring.

Fiber optic extrinsic Fabry-Perot interferometric (EFPI) sensors are ideal candidates for on-line partial discharges (PDs) monitoring due to their inherent advantages, such as immunity to electromagnetic interference (EMI), highly compact sensing probes, and remote signal transmission. However, up to date, the design and fabrication of high-performance sensing diaphragms still remain challenging, and most of the reported diaphragms utilize circular structures with the peripheral sidewalls completely fixed. Herein, a novel EFPI ultrasonic sensor for on-line PDs monitoring is demonstrated. The proposed sensing diaphragm combines a silicon beam-supported diaphragm and a fixed boundary ring with a thickness of 5 µm, which was optimized through the multi-objective genetic algorithm (MOGA) revealing its high design flexibility and manufactured by using the microelectromechanical systems (MEMS) processing technology on a silicon-on-insulator (SOI) wafer. Compared with the circular and beam-supported diaphragm, the developed structure exhibits a higher sensitivity. The testing results show that the developed sensor owns the sensitivity and noise-limited minimum detectable ultrasonic pressure (MDUP) of -10 dB re. 1V/Pa and 63 µPa/sqrt(Hz) at its designed resonant frequency, respectively. Finally, the sensor's ability to detect PDs is validated in a temporary built PDs experimental environment, further proving its great potential to perform the on-line PDs monitoring.