Polydimethylsiloxane diaphragm-based fiber ultrasonic sensor with high sensitivity and wide spectrum response range

In order to effectively enhance the sensitivity and response range of optical fiber Fabry–Pérot (FP) ultrasonic sensors, this article proposes an implementation method of an optical fiber FP ultrasonic sensor with a controllable cavity length and variable diaphragm. On the basis of optimizing the viscosity coefficient of the polydimethylsiloxane (PDMS) material, a PDMS diaphragm with the thickness ranging from 20 to 60 µm is fabricated on the end face of a Φ200/128 µm hollow glass tube using a multiple transfer method. Then, a piece of Φ125 µm single-mode optical fiber is threaded into the hollow glass tube from the other end and encapsulated to form an optical fiber FP ultrasonic sensor based on a PDMS diaphragm. The intensity of the corresponding ultrasound signal and its spectral characteristics can be inverse-analyzed by detecting the FP interference spectra formed on the fiber end and the PDMS diaphragm surface under the action of dynamic ultrasound signals. The experimental results show that the highest ultrasonic detection frequency response of the proposed PDMS diaphragm optical fiber FP ultrasonic sensor can reach 430 kHz and the signal-to-noise ratio can reach up to 70 dB. The above-mentioned results indicate that the optical fiber FP ultrasonic sensor with a PDMS diaphragm proposed in this article has obvious advantages in terms of sensitivity and response range.