Noise-insulating structures based on supercells and chirped lattices enhanced via tuning of local coupling

Abstract

Acoustic metamaterials and phononic crystals have proven themselves to be highly promising for the development of next-level noise-mitigation systems. One of the main challenges limiting the implementation of such structures is a typically narrow operational frequency range. In this work, we consider a periodic system consisting of locally coupled Helmholtz resonators and demonstrate that positions and widths of stop-bands can be adjusted via tuning of the coupling strength. Several approaches are developed, including the introduction of the chirped structures, supercells, or resonators with enhanced intrinsic losses. We numerically and experimentally demonstrate that tuning of local coupling leads to a merging of stop-bands, resulting in broadband noise-insulation within the operational range covering about 3.5 octaves. This property is linked to band structures of the associated infinitely periodic structures and discussed in terms of band-gap engineering. The low filling factor of the unit cells also suggests that the considered structures can be ventilated, which is demonstrated numerically.