Ultra-low and ultra-broad-band nonlinear acoustic metamaterials

TLDR

Linear acoustic metamaterials manipulate sound, but achieving bandgaps with a generalized width greater than one via linear mechanisms is difficult. The study aims to characterize the nonlinear chaotic mechanism in 1D and 2D nonlinear acoustic metamaterials using theoretical and experimental methods. The authors use theoretical and experimental methods to reveal a nonlinear chaotic mechanism that allows NAMs to suppress wave transmission by 20–40 dB across ultra‑low, ultra‑broad bands comprising bandgaps and chaotic bands. The resulting NAMs achieve generalized widths of 21 in 1D and 39 in 2D, surpassing current LAM bandwidth limits, and open new possibilities for double‑ultra acoustic manipulation.

Abstract

Linear acoustic metamaterials (LAMs) are widely used to manipulate sound; however, it is challenging to obtain bandgaps with a generalized width (ratio of the bandgap width to its start frequency) >1 through linear mechanisms. Here we adopt both theoretical and experimental approaches to describe the nonlinear chaotic mechanism in both one-dimensional (1D) and two-dimensional (2D) nonlinear acoustic metamaterials (NAMs). This mechanism enables NAMs to reduce wave transmissions by as much as 20-40 dB in an ultra-low and ultra-broad band that consists of bandgaps and chaotic bands. With subwavelength cells, the generalized width reaches 21 in a 1D NAM and it goes up to 39 in a 2D NAM, which overcomes the bandwidth limit for wave suppression in current LAMs. This work enables further progress in elucidating the dynamics of NAMs and opens new avenues in double-ultra acoustic manipulation.