Acoustic metamaterial absorbers based on multi-scale sonic crystals

Abstract

In this work, thermoviscous losses in single- and multi-scale sonic crystal arrangements are examined, enabling the fabrication and characterization of acoustic metamaterial absorbers. It will be shown that higher filling fraction arrangements can be used to provide a large enhancement in the complex mass density and loss factor, and can be combined with other sonic crystals of different sizes to create multi-scale structures that further enhance these effects. To realize these enhanced properties, different sonic crystal lattices are examined and arranged as a layered structure or a slab with large embedded inclusions. The inclusions are made from either a single solid cylinder or symmetrically arranged clusters of cylinders, known as magic clusters, which behave as an effective fluid. Theoretical results are obtained using a two-step homogenization process, by first homogenizing each sonic crystal to obtain the complex effective properties of each length scale, and then homogenizing the effective fluid structures to determine the properties of the ensemble structure. Experimental data from acoustic impedance tube measurements will be presented and shown to be in excellent agreement with the expected results. [Work supported by the US ONR and Spanish MINECO.]