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.
Highlights
Linear acoustic metamaterials (LAMs) are widely used to manipulate sound; it is challenging to obtain bandgaps with a generalized width >1 through linear mechanisms
We report on nonlinear acoustic metamaterials (NAMs) based on the chaotic band that achieves double-ultra band wave suppression
As elucidated by the sketched band structure of the diatomic model (Fig. 1a, b), we propose 1D and 2D NAMs with
Summary
Linear acoustic metamaterials (LAMs) are widely used to manipulate sound; it is challenging to obtain bandgaps with a generalized width (ratio of the bandgap width to its start frequency) >1 through linear mechanisms We adopt both theoretical and experimental approaches to describe the nonlinear chaotic mechanism in both onedimensional (1D) and two-dimensional (2D) nonlinear acoustic metamaterials. The passbands higher than these nonlinear LR bandgaps become chaotic and wave propagation is suppressed; an ultra-low and ultra-broad (double-ultra) band NAM is obtained. We report on NAMs based on the chaotic band that achieves double-ultra band wave suppression We design both a 1D NAM beam and a 2D NAM plate with periodic strongly nonlinear sub-wavelength meta-cells. Bifurcations, Lyapunov exponents and different experiments, we describe the propagation of waves and demonstrate that the double-ultra effect is induced by the chaotic waves
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