Abstract
In this paper, we present the theoretical analysis and the design of cylindrical multilayered electromagnetic cloaks based on the scattering cancellation technique. We propose at first the analysis and the design of bi-layered cylindrical shells, made of homogenous and isotropic metamaterials, in order to effectively reduce the scattered field from a dielectric cylindrical object. The single shell and the bi-layered shell cases are compared in terms of scattering reduction and loss effects. The comparison shows that the bi-layered configuration exhibits superior performances. The scattering cancellation approach, is, then, extended to the case of generic multilayered cylindrical shells, considering again homogeneous and isotropic metamaterials. The employment of the proposed technique to the case of cloaking devices working at multiple frequencies is also envisaged and discussed. Finally, some practical layouts of cylindrical electromagnetic cloaks working at optical frequencies are also proposed. In these configurations, the homogenous and isotropic metamaterials are replaced by their actual counterparts, obtained using alternating stacked plasmonic and non-plasmonic layers. The theoretical formulation and the design approaches presented throughout the paper are validated through proper full-wave numerical simulations.
Highlights
The possibility to synthesize properly engineered cloaks of invisibility by employing metamaterials and plasmonic media has determined a growing interest in the study of transparency and scattering-free phenomena
The approach relying on conformal mapping techniques is quite elegant and has led to some successful results, both at optical and microwave frequencies [3]–[5]
Since we are interested in a configuration working at optical frequencies, we firstly considered a dielectric cylindrical object of finite length L = 500 nm and radius r1 = 30 nm made of silica (SiO2) and illuminated by a monochromatic plane wave at the frequency of 600 THz
Summary
The possibility to synthesize properly engineered cloaks of invisibility by employing metamaterials and plasmonic media has determined a growing interest in the study of transparency and scattering-free phenomena. Some issues related to this approach concern the operative bandwidth, the losses, and the complex design of the covers, based on inhomogeneous and anisotropic materials Such drawbacks limit the valuable cloaking effect to a narrow range of frequencies and to a given polarization. The scattering cross section of a given object can be, drastically reduced by employing plasmonic and metamaterial cloaks, which can suppress the multi-polar scattering of relatively electrically large objects by exploiting the unusual properties of their local negative polarizability This approach has the advantage of using homogeneous covers, reducing the complexity of the design, and is not based on intrinsically resonant phenomena, providing good performances in terms of bandwidth and response to geometric variations [8, 9] and losses. Some results obtained through proper full-wave simulations are presented, in order to validate the proposed theoretical approach and to show its applicability to the case of multi-frequency cloaking operation
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