We report a new paradigm, via a decoupled approach, in the design of acousto-mechanical multifunctional metamaterials.

The reduction of noises, achieved through absorption, is of paramount importance to the well‐being of both humans and machines. Lattice structures, defined as architectured porous solids arranged in repeating patterns, are emerging as advanced sound‐absorbing materials. Their immense design freedom allows for customizable pore morphology and interconnectivity, enabling the design of specific absorption properties. Thus far, the sound absorption performance of various types of lattice structures are studied and they demonstrated favorable properties compared to conventional materials. Herein, this review gives a thorough overview on the current research status, and characterizations for lattice structures in terms of acoustics is proposed. Till date, there are four main sound absorption mechanisms associated with lattice structures. Despite their complexity, lattice structures can be accurately modelled using acoustical impedance models that focus on critical acoustical geometries. Four defining features: morphology, relative density, cell size, and number of cells, have significant influences on the acoustical geometries and hence sound wave dissipation within the lattice. Drawing upon their structural‐property relationships, a classification of lattice structures into three distinct types in terms of acoustics is proposed. It is proposed that future attentions can be placed on new design concepts, advanced materials selections, and multifunctionalities.

In practical engineering, noise and impact hazards are pervasive, indicating the pressing demand for materials that can absorb both sound and stress wave energy simultaneously. However, the rational design of such multifunctional materials remains a challenge. Herein, inspired by cuttlebone, we present bioinspired architected metamaterials with unprecedented sound-absorbing and mechanical properties engineered via a weakly-coupled design. The acoustic elements feature heterogeneous multilayered resonators, whereas the mechanical responses are based on asymmetric cambered cell walls. These metamaterials experimentally demonstrated an average absorption coefficient of 0.80 from 1.0 to 6.0 kHz, with 77% of the data points exceeding the desired 0.75 threshold, all with a compact 21 mm thickness. An absorptance-thickness map is devised for assessing the sound-absorption efficiency. The high-fidelity microstructure-based model reveals the air friction damping mechanism, with broadband behavior attributed to multimodal hybrid resonance. Empowered by the cambered design of cell walls, metamaterials shift catastrophic failure toward a progressive deformation mode characterized by stable stress plateaus and ultrahigh specific energy absorption of 50.7 J/g—a 558.4% increase over the straight-wall design. After the deformation mechanisms are elucidated, a comprehensive research framework for burgeoning acousto-mechanical metamaterials is proposed. Overall, our study broadens the horizon for multifunctional material design.

Acoustic metamaterials with broadband sound-absorbing capacity open up applications in aerospace, automotive, marine, defense, etc. For such applications, sound-absorbing materials that can withstand complex loading conditions are essential. Hence, to address acoustic and mechanical requirements simultaneously, we propose plate-reinforced dual-functional micro-lattice metamaterials (PDMMs) that exhibit elastic isotropy, dual crushing stages with a specific energy absorption up to 25.82 kJ/kg, and ultra-broadband sound absorption from 0.97 kHz to 6.30 kHz. The remarkable elastic isotropy lies in the topology-induced structural stiffness homogenising effect. The transition from single to dual plateau anti-compression stages is controlled by tailoring the structural local strength. On-demand broadband sound absorption is achieved by modulating the parallel coupling and cascade resonance effects, and the physical mechanism is revealed by examining impedance matching and system damping states. Overall, the presented novel metamaterials exhibit exceptional application potentials by overcoming the trade-offs usually found in traditional mechanical and acoustic metamaterials.