Omnidirectional broadband acoustic absorber based on metamaterials

We present the design, construction, and experimental characterization of the acoustic analogue of the so called photonic black-hole. The fabricated sample has cylindrical symmetry and consists of two parts, a shell that bends the sound towards the center and a core that dissipates its energy. The shell is made of a metamaterial that perfectly matches the acoustic impedance of air and behaves like a gradient index lens. The experimental data obtained in a multi-modal impedance chamber demonstrate that the proposed acoustic black-hole acts like an onmidirectional broadband absorber with strong absorbing efficiency.