Noncontact Ultrasonic Detection in Low-Pressure Carbon Dioxide Medium Using High Sensitivity Fiber-Optic Fabry–Perot Sensor System

For the application of ultrasonic detection in low-pressure carbon dioxide medium, we propose a fiber-optic Fabry-Perot (F-P) ultrasonic sensor system based on an edge-stretched circular polymer diaphragm. The diaphragm is fabricated with pre-tension of 200 N/m. The demonstrated demodulation system is based on quadrature phase-shifted demodulation method. By setting the F-P cavity length and the wavelengths of distribute feedback (DFB) semiconductor lasers, two quadrature-phase interference signals can be obtained. Experimental results showed that the proposed sensor system can have a sensitivity of 10.4 nm/kPa and a signal-to-noise ratio (SNR) of 14.45 dB under gas pressure of 270 Pa in low-pressure carbon dioxide. The unique advantages of the proposed sensor system make it attractive for non-contact ultrasonic detection in low-pressure gas medium.