ABSTRACT
Longwave infrared spectral imaging (LWIR-SI) has potential in many important civilian and military fields. However, conventional LWIR-SI systems based on traditional dispersion elements always suffer the problems of high cost, large volume and complicated system structure. Micro-electro-mechanical systems Fabry-Perot filtering chips (MEMS-FPFC) give a feasible way for realizing miniaturized, low cost and customizable LWIR-SI systems. The LWIR MEMS-FPFC ever reported can't meet the demands of the next-generation LWIR-SI systems, due to the limitation of small aperture size and nonlinear actuation. In this work, we propose a large-aperture, widely and linearly tunable electromagnetically actuated MEMS-FPFC for LWIR-SI. A multi-field coupling simulation model is built and the wafer-scale bulk-micromachining process is applied to realize the design and fabrication of the proposed MEMS-FPFC. Finally, with the rational structural design and fabrication process, the filtering chip after packaging has an aperture size of 10 mm, which is the largest aperture size of LWIR MEMS-FPFC ever reported. The fabricated electromagnetically actuated MEMS-FPFC can be tuned continuously across the entire LWIR range of 8.39-12.95 µm under ±100 mA driving current with a pretty good linear response of better than 98%. The developed electromagnetically actuated MEMS-FPFC can be directly used for constructing miniaturized LWIR-SI systems, aiming for such applications as military surveillance, gas sensing, and industry monitoring.
ABSTRACT
Ultrasonic wave is a powerful tool for many applications, such as structural health monitoring, medical diagnosis and partial discharges (PDs) detection. The fiber optic extrinsic Fabry-Perot interferometric (EFPI) sensor has become an ideal candidate for detecting weak ultrasonic signals due to its inherent advantages, and each time with a performance enhancement, it can bring great application potential in broadened fields. Herein, an EFPI ultrasonic sensor for PDs detection is proposed. The sensing diaphragm uses a 5-µm-thickness and beam-supported structure to improve the responsive sensitivity of the sensor at the resonant frequency. Furthermore, the ability of the sensor to detect characteristic ultrasonic signal of PDs is further enhanced by assembling a Fresnel-zone-plate (FZP)-based ultrasonic lens with the sensing probe to amplify the ultrasonic wave before it excites the sensing diaphragm. The final testing results show that the originally developed sensor owns the sensitivity of - 19.8 dB re. 1 V/Pa at resonant frequency. While, when the FZP is assembled with the probe, the sensitivity reaches to - 12.4 dB re. 1 V/Pa, and leads to a narrower frequency band, which indicates that the proposed method has a great potential to enhance the detection ability of sensor to characteristic ultrasonic wave of PDs.
ABSTRACT
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.
