Fiber Optic Fabry–Perot Ultrasonic Sensor for Solid-State Ultrasonic Detection

A thin-walled microsphere-type Fabry–Perot interference (TWMT-FPI) fiber optic sensor was proposed, and it could be constructed by stretching to break a simple Fabry–Perot interferometer made by single-mode fiber (SMF) and hollow-core fiber (HCF) to form a conical cavity structure (CCS) and discharging CCS multiple times in fiber fusion machine. The sensing principle of the proposed structure was studied theoretically, and its ultrasonic response characteristics were investigated by experiments. The experimental results show that the structure is not only capable of effectively detecting continuous and pulsed ultrasound signals in solids but also has a wide frequency response range from 300 kHz to 3 MHz. For continuous and pulsed ultrasound signals of 2 MHz, the signal-to-noise ratios (SNR) of the structure are as high as 66.5 and 67.6 dB, which can be improved by gold plating of the structure.