Reconfigurable Acoustic Absorber Comprising Flexible Tubular Resonators for Broadband Sound Absorption

Typical acoustic metamaterial absorbers rely on relatively rigid materials for acoustic resonances, which, however, poses a challenge in reshaping and reconfiguring them. Here, we demonstrate soft reconfigurable acoustic absorbers, which are realized by the use of flexible tubular resonators. Owing to the structural compliance, the tube absorbers promote intriguing acoustic-structure coupling and exhibit hybrid resonances of acoustic and structural modes, which are characterized by Rabi splitting in the strong-coupling regime and Fano-like resonance in the weak-coupling regime. Also, the soft walls of the flexible resonators induce decreased resonance frequencies for low-frequency absorption by reducing the effective sound speed inside the tube. Moreover, we find that these hybrid resonances are critically influenced by the structural loss of the flexible resonators. While elucidating the role of the material rigidity and structural loss in acoustic resonances, this work allows us to design versatile broadband absorbers that can be reconfigured depending on the topology of a target substrate.