Sound Mitigation by Metamaterials With Low-Transmission Flat Band

Space-coiling acoustic metamaterials dominated by the Fano resonance are being widely exploited for simultaneous control of sound isolation and air ventilation, and they usually achieve complete sound mitigation at multiple isolated frequencies. Here, we theoretically discover and experimentally demonstrate the low-transmission flat-band phenomenon in channeling-type acoustic metamaterials. The metamaterial is constructed with coupled coiling and straight channels, both working in acoustic resonant states. An analytic coupled-mode model is established to capture the coupling interaction between resonant states supported by two channels. A critical coupling condition is derived from the model, which can lead to sextremely low sound transmission in a finite band rather than at isolated frequencies, as validated by both numerical simulations and experiments. We then demonstrate the generality of the flat-band behavior of low transmission by a systematic survey of the coupling of different order resonant modes. Finally, the flat-band effect is also found to exist in the extended model with the side-loaded coiling channel as verified experimentally.