Acoustic metastructure-enabled ventilation and low-frequency absorption in porous materials

We investigate an acoustic metastructure that improves porous sound-absorbing materials for low-frequency sound absorption and ventilation capabilities. Our structure encloses the porous materials with a perforated front plate and a partitioned back cavity. The porous materials are shaped into cuboid pieces for easier modification and adaptation within the cavity ends. This design enables the resonance of the porous materials not by their thickness but due to the enclosing metastructure. It facilitates significant energy dissipation of low-frequency waves in the porous domain, allowing the metastructure to adjust its acoustic resistance with the type and length of the porous material. Consequently, our metastructure coherently achieves near-perfect sound absorption across various porous materials that differ in their resistive properties. Moreover, the proposed structure maintains its absorption properties with a ventilation passage, further highlighting its ventilated noise attenuation performance compared to bulk porous materials.