Ultrasensitive and Wideband Ultrasonic Sensor Based on Micro-Multicore Fiber

A micro-multicore fiber (MMCF) encapsulated in polydimethylsiloxane (PDMS) is proposed and demonstrated for ultrasonic sensing based on mode interference effects. The large evanescent field and compact size of the microfiber serve as a bridge between optics and acoustics. Due to the high elastic-optic coefficient of PDMS, the minimum detectable pressure level (MDPL) of the 9 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$\mu$</tex-math></inline-formula> m MMCF sensor is 30.9<inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$\rm { mPa/H}{{\mathrm{{z}}}^{\mathrm{{1/2}}}}$</tex-math></inline-formula> at the frequency of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$ \sim$</tex-math></inline-formula>5 MHz. The sensor exhibits a broad response with a -6 dB bandwidth of approximately 8 MHz. Furthermore, its promising application in partial discharge (PD) detection has been verified, demonstrating its capability to detect ultrasonic signals generated by a discharge of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$ \sim$</tex-math></inline-formula>36 pC. Owing to their high sensitivity, wide bandwidth, cost-effectiveness, and facile fabrication, MMCF-based sensors present a competitive solution for diverse applications, including PD monitoring, industrial nondestructive testing, seismic physical modeling, and photoacoustic imaging.