Design, manufacture, and characterisation of hierarchical metamaterials for simultaneous ultra-broadband sound-absorbing and superior mechanical performance

For engineering applications, sound-absorbing materials are supposed to withstand potential impact loading conditions. However, there is a lack of attempts on multifunctional metamaterials for both acoustic and mechanical purposes. Herein, a hierarchical metamaterial manufactured by fused deposition modelling (FDM) that exhibits simultaneous acoustic and mechanical energy-absorbing capacities is proposed in this work. The metamaterial obtains a successively increasing absorption bandwidth with the growth of the hierarchical order. Ultra-broad half-absorption band from 0.96 to 6.00 kHz is obtained for the fourth order. The unique resonant responses are demonstrated analytically, numerically, and experimentally via properly modulating the structural features. The enhancement mechanism is physically revealed by analysing the impedance matching and resonant damping states. Moreover, compared with its original counterpart, the specific energy absorption (SEA) of the first-order and the second-order hierarchical metamaterials increases by 228% and 434%, respectively. This work provides an effective approach for designing multifunctional metamaterials.