Abstract
A design strategy and its modeling for high-transmission acoustic self-focusing and directional cloaking in a two-dimensional (2D) and an axisymmetric three-dimensional (3D) gradient-index phononic crystal (GRIN-PC) are reported in this paper. A gradient perforated aluminum slab sandwiched by water is considered. A low-loss directional cloaking device is achieved by controlling the matching coefficient between the slab and the water. The anisotropy coefficient that affects the scattering properties is also introduced. Furthermore, the phase discontinuity for directional cloaking inside and outside the slab is overcome by introducing a non-gradient slab having a lower group velocity behind the GRIN slab as an acoustic delay device. In addition, an axisymmetric 3D directional cloaking structure is obtained by rotating the corresponding 2D structure around the slab axis.
Highlights
Optical or acoustical invisibility devices can keep objects undetectable to electromagnetic or sound waves
The present directional cloaking is designed based on the gradient-index phononic crystal (GRIN-phononic crystals (PCs)) that can control the incident wave to propagate around the cloaking area
The block on the corner is divided into two branches and the dispersed distribution can broaden the adjustable range of the filling ratio
Summary
Optical or acoustical invisibility devices can keep objects undetectable to electromagnetic or sound waves. The focal length is set as L = 11a, and the initial refractive index n0 is assumed to be 1.161 corresponding to the parameter d = 0.5a at the frequency of 25 kHz. based on Equations (2) and (3), the wave vector magnitude along the y-axis is obtained and the variable parameter d is calculated numerically.
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