Ventilated noise-insulating metamaterials inspired by sonic black holes

Sonic black holes represent a special class of metastructures allowing efficient absorption based on the slow sound principle. The decrease in the wave speed in this case is associated with the spatial variation of the acoustic impedance, whereas the absorption properties are linked to thermoviscous losses induced by the local resonances. Typically, sonic black holes are considered as axially symmetric structures consisting of solid rings with a coordinate-dependent radius. This work is dedicated to the development of noise-insulating structures that have a geometry similar to a sonic black hole with a rectangular cross section. Transmission loss in this case is associated with the local coupling between the resonators constituting meta-atoms, which results in the occurrence of broad stop-bands in transmission spectra of the structure. A realistic application scenario of a ventilated duct is considered such that a fan simultaneously generates acoustic noise and air flow. The structure embedded in the duct is shown to demonstrate efficient noise insulation within the spectral range of 1000 – 2850 Hz, while the air flow speed is reduced by just 25%.