Ventilated metamaterials for broadband sound insulation and tunable transmission at low frequency

Metamaterials enabling multifunctional wave control have long attracted great interest, but remain largely unexplored in ventilation-required settings. Using the space-coiling strategy, we design and fabricate a compact acoustic meta-structure consisting of labyrinth resonators arranged around a central air passage. Such meta-structures provide a promising route to design well-ventilated and simultaneously highly-effective sound-proofing barriers allowing broadband (about one octave band) transmission loss up to almost 30 dB in the range of 660–1200 Hz. More interestingly, due to the interferences between the forward propagating waves and those re-radiated by the surrounding resonators, some asymmetric Fano-like resonances are observed appearing in the transmission gap. This Fano-like resonance is very useful to open a high transmission window at frequencies of interest by changing the length of coiled-up channels. Our findings are both numerically and experimentally verified, which may stimulate multifunctional applications, such as broadband sound insulation with high transmission loss and tunable acoustic communication, especially in ventilation-required environments.