A nonlinear metamaterial plate for suppressing vibration and sound radiation

Nonlinear acoustic metamaterials (NAMs) exhibit extraordinary properties for low-frequency and broadband vibration mitigation. Despite the increasing attention received, exotic properties and the physical mechanisms underpinning NAM-enabled functionalities have not been fully understood. Moreover, investigations on the sound radiation of NAM structures have not been reported. Here we systematically investigate the vibration of a NAM plate and its sound radiation using experimental and theoretical methods. We experimentally demonstrate that the NAM plate can entail significant vibration and sound radiation reduction in an ultra- low and broad frequency band, typically from 20 to 1800 Hz, without any artificial damping element. This is attributed to the nonlinear coupling among multiple local resonances, and the nonlinear collision-friction damping. This understanding allows the proposal of two design strategies to achieve ultra- low and broadband vibration and sound radiation suppression with NAMs. Moreover, we clarify the mechanisms governing the ultra- low and broadband features, including bandgaps, output saturation of nonlinear resonances, efficient energy pumping due to high-order harmonics and chaos, and modulation of nonlinear resonance modal amplitudes and shapes. These mechanisms and diverse wave behaviors are inter-related and occur concurrently. The reported study provides answers to several key questions of paramount importance in designs, mechanics and applications of nonlinear metamaterials.