Sound-Absorbing Materials

Sound-absorbing materials (SAMs) have attracted significant interest for more than a century owing to their rich physical properties and extensive potential in acoustic engineering. This article provides an overview of recent progress in and future prospects for SAMs, from single resonators to coupled resonant systems. Single resonant SAMs use resonances to achieve high-efficiency absorption in a certain bandwidth with a significantly smaller thickness than porous SAMs. The emergence of sound-absorbing metamaterials has led to further thinner structures at deep-subwavelength scales. Coupled resonant systems offer new opportunities for broadband sound absorption and multifunctionality. We introduce the conservation equations for single resonators and general SAMs, outlining the design strategies for achieving tunable and broadband SAMs approaching the optimal conditions governed by the conservation equations. We also review recent developments in multifunctional SAMs and metaliners. Finally, we provide an outlook on potential directions and applications for future work in this rapidly evolving field.