Quasi-periodic sonic black hole with low-frequency acoustic and elastic bandgaps

Metamaterials with the capability to control wave propagation in fluid or solid mediums have attracted plenty of fundamental scientific and engineering research in recent decades. This paper proposes a novel metamaterial, named Quasi-periodic sonic black hole (Q-SBH), to achieve both acoustic bandgap and elastic bandgap. The Q-SHB consists of two functional units: outer soft shells and inner stiff rings. The stiff rings with decaying inner radii are connected by soft shells, and the distances between rings take linear variation. The Q-SBH reserves the slow-sound effect of sonic black hole and the non-uniformly distributed rings serve as mistuning vibration absorbers. On the basis of these characteristics, broadband low-frequency acoustic and elastic bandgaps are generated simultaneously. We demonstrate the attenuation performance of the Q-SBH by theoretical, numerical and experimental methods. Parametric analysis and multi-objective optimization of the structure are carried out. The results demonstrate the great potential of the proposed Q-SBH in a broad range of physical fields requiring both air-borne noise reduction and structural vibration suppression.