Design, Fabrication, Characterization, and Application of an Ultra-High Temperature 6H-SiC Sapphire Fiber Optic Vibration Sensor

A 6H-SiC Sapphire fiber optic vibration sensor that can work at 1200 °C was designed, fabricated and tested in this paper. A sapphire fiber and a 6H-SiC vibration-sensitive element constituted the Fabry–Perot resonant cavity. The laser was input via the sapphire fiber, enabling the vibration signal to be converted to an optical signal through the Fabry–Perot cavity, and the vibration parameters were obtained by optical demodulation. The vibration-sensitive element consisted of a cantilever structure, whose structure parameters were determined by the combination of theoretical analysis and simulation. A nanosecond laser was employed to fabricate the 6H-SiC vibration-sensitive element to improve the processing efficiency and simplicity. The sensor was tested from room temperature to 1200 °C. The results showed that its frequency measurement sensitivity remains 0.9997 Hz/Hz from room temperature to 1200 °C, with the full-scale precision being 0.44% F.S. The sensor's output voltage is linearly correlated with the vibration acceleration from ambient temperature to 800 °C, making the acceleration measurement sensitivity 17.86 mV/g at 800 °C. The maximum frequency measurement error was 4.72 Hz when the sensor was at the field application of high temperature casting.