Metasurface-Enhanced Fiber-Optic Distributed Acoustic Sensing

Fiber-optic distributed acoustic sensing (DAS), a burgeoning technology that converts optical fiber to acoustic sensing array, provides a revolutionary distributed sensing way for acoustic detection. Despite the research undertaken on sensing cables for DAS sensitivity enhancement, applying passive acoustic manipulation array for enhancing DAS response remains untapped. Acoustic metasurface is a new kind of artificial structure with subwavelength thickness and capable of offering non-trivial local phase shift or amplitude modulation. Here, we propose and demonstrate a novel concept for improving the DAS sensitivity with the acoustic metasurface, for the first time. Due to the non-resonant dispersion and high transmission, the tapered labyrinthine structures are used to build the '0' and '1' elements of the coding metasurface which forms an acoustic lens. The incident acoustic waves are focused on the DAS sensing unit that is constructed by a hollow cylindrical elastomer with optical fiber helically wound on its surface. The metasurface-enhanced DAS concept is validated via the simulation and test of a 3D printed metasurface structure. Experimental results indicate that the DAS sensitivity is significantly improved by nearly 10 dB over a relatively wide frequency range of 810 Hz due to the focusing effect of metasurface. This work proves the feasibility of the metasurface-enhanced DAS and shows its potential to be applied to weak airborne, or underwater acoustic signal detection.