Acoustic sensing enhancement and directional acoustic localization based on nonlinear compact gradient coiled metamaterials

Abstract

Acoustic sensing has always been a research hotspot, in which how to break the detection limit is the key to research. Although the emergence of acoustic metamaterials in recent years has solved some of these problems, the current acoustic metamaterials still exhibit the issues, such as the excessive size and mismatches between wave vectors of the waveguide and surrounding media. To address these issues, a nonlinear compact gradient coiled metamaterial (NCGCM) is proposed in this paper. In the designed NCGCM structure, a nonlinear variation in air gap depth is employed to avoid the wave vector mismatch. The linear variation in the thickness of the acoustic grating ensures the grating stiffness and prevents the acoustic-solid coupling, and a linear change in air gap width reduces the heat loss. The linear variation in the thin plate length of the air gap can improve the refractive index to ensure the acoustic enhancement effect. The acoustic simulation of the NCGCM structure is modeled in the Comsol software. The simulation results verified that the NCGCM structure has the good frequency selectivity, acoustic enhancement effect and the good directional response ability. It can effectively identify and capture weak harmonic signals and Gaussian pulse signals. The NCGCM structure provides a new idea for the detection of weak acoustic signals and the directional acoustic localization. The designed NCGCM structure is fabricated in its entirety by 3D printing using photosensitive resin material, and an experiment is employed to further validate its capability.