# Space-time Variant Self-growing Bandgap in Nonlinear Acoustic Metamaterial

## TL;DR

This paper introduces a nonlinear acoustic metamaterial with a self-adapting, self-growing bandgap that varies over space and time, enabling ultrabroad and ultralow frequency ranges for wave manipulation.

## Contribution

It reports the first nonlinear acoustic metamaterial with a self-growing, space-time variant bandgap, surpassing traditional linear limitations and enabling advanced wave control.

## Key findings

- Demonstration of a self-adapting, self-growing bandgap in nonlinear acoustic metamaterials.
- The bandgap exceeds linear mass law limitations, achieving ultrabroad and ultralow frequencies.
- Elucidation of the mechanisms behind the space-time self-modulation of the band structure.

## Abstract

Material band structure is key foundation for various modern technologies, but it was regarded as a space-time invariant feature. Acoustic metamaterials show extraordinary properties for processing elastic waves, but conventional realizations suffer from narrow bandgaps. Here we first report a nonlinear acoustic metamaterial whose band structure self-adapts to the propagation distance/time and the bandgap exhibits a self-growing behaviour stemming from giant nonlinear interaction. This space-time self-modulating characteristic highlights an unconventional understanding of the band structure, and the self-growth generates an ultralow and ultrabroad bandgap that breaks through the limitation of the mass law for linear locally resonant bandgaps. We also elucidate the self-adaptive mechanisms. This first demonstration sheds light on conceiving advanced devices and metamaterials with broadband, space-time variant bandgaps for wave self-manipulation.

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Source: https://tomesphere.com/paper/1907.03062