High-efficiency ventilated metamaterial absorber at low frequency

We demonstrate a ventilated metamaterial absorber operating at low frequency (<500 Hz). With only two layers of absorption units, high-efficiency absorption (>90%) has been achieved in both simulations and experiments. This high-efficiency absorption under the ventilation condition originates from the weak coupling of two identical split tube resonators constituting the absorber, which leads to the hybridization of the degenerate eigenmodes and breaks the absorption upper limit of 50% for conventional transmissive symmetric acoustic absorbers. The absorber can also be extended to an array and work in free space. The absorber should have potential applications in acoustic engineering where both noise reduction and ventilation are required.