Anisotropic density-near-zero metamaterials for enhanced directional and aperture-adjustable acoustic emission.

We report a design of enhanced directional emission (EDE) based on anisotropic metamaterial (MM). The proposed material consists of a square array of cuboids and is theoretically and numerically shown to yield zero components of the effective density tensor, hence can be designed to realize an EDE. The influences of device shape on the directive beaming are discussed. The desirable EDE with our proposed devices is realized and, due to the total internal reflection, the beam aperture is able to be adjusted by modifying the external shape of devices. Besides, the influences of geometric parameters of microstructures on the working frequency are discussed in detail. This proposed MM may have applications in acoustic antenna, acoustic cloak and noise control. [ABSTRACT FROM AUTHOR]