Broadband vibration attenuation via nonlocal acoustic black hole metastructures

In recent years, the application of Acoustic Black Holes (ABH) to passive vibration attenuation, vibroacoustic control, and vibration-based energy harvesting of thin walled structures has seen a rapidly growing interest. It is well known that the dynamic operating range of an ABH is limited by the existence of a cut-on frequency below which the ABH is not effective. The specific value of this frequency bound is connected to the ABH characteristic dimension, typically its diameter. In order to expand the dynamic operating range and lower the cut-on frequency, ABH features require larger diameters. However, design and manufacturing constraints impose stringent limitations that are often incompatible with required ABH dimensions. This work introduces the concept of nonlocal ABH metastructures and explores the feasibility of using intentionally introduced nonlocality to extend the dynamic operating range of periodic ABH lattices towards the lower frequencies. The role of nonlocality is investigated via a dedicated semi-analytical model, and the dynamic performances of different nonlocal designs are studied numerically. Results show a remarkable ability of the nonlocal design to expand the operating range of the ABH metastructure and to achieve vibration attenuation behavior at frequencies significantly below the cut-on frequency of the individual ABH.