A programmable acoustic metamaterial: achieving untethered ultra-broadband modulation with photoactive structural transition

The increasing global concern over low-frequency noise pollution necessitates innovative solutions capable of effective acoustic attenuation across varying environments. However, conventional acoustic metamaterials, characterized by fixed geometries, typically provide limited flexibility in adjusting the functional frequency range once constructed. This study revisited the classic acoustic metamaterial configurations and proposed two novel tunable acoustic absorbing structures through a strategic integration with high-performance photo-active polymer actuators. The research detailed how the soft intelligent materials were leveraged to facilitate the structural transition across different metamaterial configurations, consequently enabling programmable ultra-broadband modulation. Both experimental measurements and finite element modeling (FEM) simulations were implemented to validate that, with the programming of the stimulation status on different monitoring elements, the absorbers can effectively transition between micro-slit resonance state and membrane resonance mode, or the MPP resonance mode and its coupling mode with a coiled channel of varied equivalent length. In particular, the proposed acoustic structure can achieve an untethered normalized frequency band modulation of up to 324.6%. This work not only signifies a pioneering application of photo-active polymers in wide-band wireless acoustic control but also lays the groundwork for adaptive noise management solutions in real-world applications.