Acoustic gradient-index lens using orifice-type metamaterial unit cells

A gradient-index (GRIN) lens made of acoustic metamaterial is described that is assembled of unit cells with specific orifice characteristics. The GRIN distribution of the lens is established using different hole sizes for the unit cells. The intensity of the sound waves is demonstrated through simulations and confirmed by an experiment in a frequency band that satisfies the homogeneous medium constraints for the metamaterial. Experimental results from the focusing of sound waves of various frequencies agreed well with the expected values from the GRIN lens equation. This face-centered-orifice-cubic unit cell, which is nearly non-dispersive but asymmetric, appears to be a useful acoustic metamaterial for various acoustic devices operating with broadband frequencies. (C) 2016 AIP Publishing LLC.