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.

非线性声学超材料 (NAM) 在低频和宽带振动缓解方面表现出非凡的特性。尽管受到越来越多的关注，但支持 NAM 功能的奇异特性和物理机制尚未完全了解。此外，还没有关于 NAM 结构声辐射的研究报告。在这里，我们使用实验和理论方法系统地研究了 NAM 板的振动及其声辐射。我们通过实验证明 NAM 板可以在超低和宽频带（通常为 20 至 1800 Hz）内显着减少振动和声音辐射，而无需任何人工阻尼元件。这归因于多个局部共振之间的非线性耦合，以及非线性碰撞摩擦阻尼。这种理解允许提出两种设计策略，以使用 NAM 实现超低和宽带振动和声音辐射抑制。此外，我们阐明了控制超低和宽带特征的机制，包括带隙、非线性共振的输出饱和、由于高次谐波和混沌引起的有效能量泵浦，以及非线性共振模态振幅和形状的调制。这些机制和不同的波浪行为是相互关联的，并同时发生。报告的研究为非线性超材料的设计、力学和应用中至关重要的几个关键问题提供了答案。我们阐明了控制超低和宽带特征的机制，包括带隙、非线性谐振的输出饱和、由于高次谐波和混沌引起的有效能量泵浦，以及非线性谐振模态幅度和形状的调制。这些机制和不同的波浪行为是相互关联的，并同时发生。报告的研究为非线性超材料的设计、力学和应用中至关重要的几个关键问题提供了答案。我们阐明了控制超低和宽带特征的机制，包括带隙、非线性谐振的输出饱和、由于高次谐波和混沌引起的有效能量泵浦，以及非线性谐振模态幅度和形状的调制。这些机制和不同的波浪行为是相互关联的，并同时发生。报告的研究为非线性超材料的设计、力学和应用中至关重要的几个关键问题提供了答案。