High-sensitivity fiber optic Fabry–Perot ultrasonic sensor based on a grooved silicon diaphragm for partial discharge detection

An extrinsic fiber optic Fabry–Perot interferometric (EFPI) ultrasonic sensor based on a grooved silicon diaphragm for partial discharge (PD) detection has been proposed. The size of the groove is determined by finite element simulation, which allows the resonant frequency of the sensor to meet the requirements of PD ultrasonic detection and improves the sensitivity of the sensor by 5.07 times compared with that based on a traditional circular diaphragm. The microelectro–mechanical system process is used to fabricate the diaphragm on a silicon-on-insulator wafer, and the prepared diaphragm has a grooved section with a diameter of 829.34 µm and a thickness of only 2.09 µm. At its resonant frequency of 61.5 kHz, the acoustic pressure sensitivity of the sensor is 172.42 mV/Pa. The ultrasonic signal detection capability of the sensor is verified in the PD experiment. Furthermore, the characteristics of the corona discharge are successfully manifested based on the ultrasonic waves detected by the EFPI sensor. It is demonstrated that the proposed sensor is suitable for PD detection due to its high sensitivity, simple production process, and good resistance to environmental interference.