Acoustic metamaterial absorbers based on multilayered sonic crystals

Through the use of a layered arrangement, it is shown that lossy sonic crystals can be arranged to create a structure with extreme acoustic properties, namely, an acoustic metamaterial. This artificial structure shows different effective fluids and absorptive properties in different orientations. Theoretical, numerical, and experimental results examining thermoviscous losses in sonic crystals are presented, enabling the fabrication and characterization of an acoustic metamaterial absorber with complex-valued anisotropic inertia. To accurately describe and fabricate such an acoustic metamaterial in a realizable experimental configuration, confining structures are needed which modify the effective properties, due to the thermal and viscous boundary layer effects within the sonic crystal lattice. Theoretical formulations are presented which describe the effects of these confined sonic crystals, both individually and as part of an acoustic metamaterial structure. Experimental demonstrations are also reported using an acoustic impedance tube. The formulations developed can be written with no unknown or empirical coefficients, due to the structured lattice of the sonic crystals and organized layering scheme; and it is shown that higher filling fraction arrangements can be used to provide a large enhancement in the loss factor. (C) 2015 AIP Publishing LLC.This work was supported by the U.S. Office of Naval Research (Award No. N000141210216) and by the Spanish Ministerio de Economia y Competitividad (MINECO) under Contract No. TEC2010-19751.Guild, M.; García Chocano, VM.; Kan, W.; Sánchez-Dehesa Moreno-Cid, J. (2015). Acoustic metamaterial absorbers based on multilayered sonic crystals. Journal of Applied Physics. 117(11):114902-1-114902-14. https://doi.org/10.1063/1.4915346S114902-1114902-1411711Dowling, J. P. (1992). Sonic band structure in fluids with periodic density variations. 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