Towards extraordinary sound absorption using coupled resonances

In this paper, we provide an overview of recent advancements in novel sound absorption designs, predominantly based on optimized coupling between resonances. First, we present a sound absorption panel design capable of achieving high absorption in the low-frequency broadband range (50–63 Hz, one-third octave band). This panel demonstrates an average absorption coefficient of approximately 93%, all while maintaining a thickness of 15.4 cm (equivalent to 1/45 of the wavelength at 50 Hz). Transitioning from the one- port system, we delve into the realm of the two-port system, introducing an ultra-sparse structure for flow-free sound absorption. This structure exhibits near-perfect absorption (∼99%), and this absorption capability is achieved when the spatial period of monopole–dipole resonators is close to one working wavelength (95% wavelength). These developments signify significant strides in sound absorption technology, presenting innovative solutions with enhanced efficiency and performance across various frequency ranges and environments.