Abstract
The optimized cloaking design for conducting cylinders of different sizes is studied based on the Mie scattering theory. We construct a concentric multi-layered cloak made of alternating materials with isotropic dielectrics and epsilon-near-zero (ENZ) material, the thickness of which can be determined through genetic algorithm. As the radius of the conducting cylinder increases, high order scattering contributions are becoming evident, and more layers are needed. The scattering cross sections of three different radii of PEC cylinders are minimized by utilizing different numbers of multi-layers respectively. We find that eight or less optimized layers can cancel most of the scattering from a conducting cylinder with its dimension compared to wavelength, and more effectively when taking the ENZ material as the inner starting shell. The frequency dependence of total scattering is also studied, leading to the result that the bandwidth decreases as the size of concealed PEC cylinder increases. Furthermore, it is shown that the cloaking efficiency is less sensitive to the permittivity and thickness of the ENZ material, due to the small phase variation in the ENZ material. The multi-layered cloak designed for a PEC target can also be used to evidently reduce the scattering of a dielectric core and design a multi-layered elliptical cloak.
Highlights
During the past decade, there has been a great deal of interest in studying the electromagnetic (EM) invisibility cloak, which can hide objects from EM detection[1,2,3,4,5,6,7,8,9,10,11]
In order to facilitate the physical implementation and conceal a moderate-sized object with maximum level of invisibility, several kinds of multi-layered cloaks based on the optimization procedures have been proposed, employing anisotropic metamaterials[12,13,14], isotropic ENZ materials[15,16], and even ordinary dielectrics[17,18,19] respectively
It was experimentally demonstrated that the ENZ material can act as a host medium doped by dielectric particles to modify the medium’s effective permeability, independently of the dopants’ position within the host[21]
Summary
There has been a great deal of interest in studying the electromagnetic (EM) invisibility cloak, which can hide objects from EM detection[1,2,3,4,5,6,7,8,9,10,11]. In contrast to the extraordinarily complex material obtained from the coordinate transformation, the scattering cancellation scheme commonly termed as plasmonic cloaking only uses one or two layers of isotropic plasmonic covers to cancel the dipole response of an object[8,9,10]. This cloaking scheme is typically limited to sub-wavelength scales, while for larger object the higher order scattering may make the cloaking performance less effective. It is possible to design the multi-layered elliptical cloak, in which the thickness of the each covering shell is the same as that of the cloak once designed for the PEC cylinder
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