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

Linear acoustic metamaterials (LAMs)are widely used to manipulate sound, but it is challenging to obtain bandgaps withthe generalized width (the ratio of the bandgap width to its start frequency) γ>1 based on linear mechanisms.Here, we adopt both theoretical and experimental approaches todescribe the nonlinear chaotic mechanism in both one-dimensional (1D) and two-dimensional (2D)nonlinear acoustic metamaterials (NAMs). This mechanismenables the strongly NAMsto reduce the transmission of wave by as much as 20-40dB in an ultra-low and ultra-broad bandthat consists of bandgaps and chaotic bands.With the subwavelength cells, the generalized width reachesγ=21 in a 1D NAM and it goes up to γ=39 in a 2D NAM, which overcomesthe limit of bandwidth for wave suppression in current LAMs.Our work allows for further progress in the understanding of the dynamics of NAMs and it opens up avenuesindouble-ultra acoustic manipulations.