Multifunctional acoustic metamaterial for air ventilation, broadband sound insulation and switchable transmission

Noise reduction and other manipulation of sound waves has been a major concern in science and engineering. Here, we propose a ventilated soundproof acoustic metamaterial consisting of resonant cavities arranged around a central air passage. This metamaterial can accomplish strong sound insulation performance. The transmission loss is larger than 30 dB within a wide frequency range (625-1695 Hz) due to the prohibited band. More intriguingly, we discover that rotating the opening, somewhat like an acoustic switch, can directly control the sound transmission of the deaf band. This is particularly useful for opening a narrow but high transmission window at the frequency of interest, which provides a new degree of freedom for sound control. Through band structure analysis and effective parameter calculation, we discover the sound insulation mechanism of the ventilated metamaterial and reveal the underlying mechanism of the switchable narrow-band sound transmission. Beyond the 1D study, the proposed acoustic metamaterial is expanded to a 3D soundproof metacage. We find that the sound insulation performance and switchable sound transmission phenomena are still retained for the metacage. The results reported here may inspire more exploration of sound barriers and multifunctional applications, such as innovative building facades for noise reduction and logic components for acoustic circuits.