An Acoustic Hyperlens with Negative Direction Based on Double Split Hollow Sphere

Abstract

This study develops a new acoustic negative-refraction metamaterial that utilizes a synthesized double split hollow sphere (DSHS) for its unit cell. Recent relevant research has affirmed the concept that acoustic metamaterials can show unusual behavior that has not been observed in nature previously. However, as some hypothetical metamaterial designs have material properties not found in nature, the realization of practical metamaterials requires practical and complicated models. As a contribution to the development of acoustic metamaterials, the present study proposes a new anisotropic unit structure that encompasses Helmholtz resonators. This structure is referred to as the DSHS, is easy to manufacture, and has the advantage in that it uses the natural medium in its original form. By drawing the equifrequency or isofrequency contours of the designed two-dimensional (2D) anisotropic unit structure using the Floquet–Bloch’s principle, the properties of the present metamaterial can be understood. Numerical simulations are also conducted to identify and present the characteristics of the presented acoustic metamaterial. Through these, a new refraction phenomenon is identified that deviates from Snell’s law, and an acoustic hyperlens is numerically implemented that overcomes the diffraction limit.