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We numerically demonstrate that properly designed plasmonic covers can be used to enhance the performance of near-field scanning optical microscopy (NSOM) systems based on the employment of apertureless metallic tip probes. The covering material, exhibiting a near-zero value of the real permittivity at the working frequency, is designed in such a way to dramatically reduce the undesired scattering due to the strongly plasmonic behavior of the tip. Though the light scattering by the tip end is necessary for the correct operation of NSOMs, the additional scattering due to the whole probe affects the signal-to-noise ratio and thus the resolution of the acquired image. By covering the whole probe but not the very tip, we show that unwanted scattering can be effectively reduced. A realistic setup, working at mid-IR frequencies and employing silicon carbide covers, has been designed and simulated to confirm the effectiveness of the proposed approach.

Here we extend the plasmonic cloaking technique to irregularly shaped objects with anisotropic scattering response. The scattering-cancellation approach to cloaking [A. Alu and N. Engheta, Phys. Rev. E 72, 016623 (2005)] has been extensively applied in the past to symmetrical geometries and canonical shapes. However, recent papers have raised some doubts concerning the fact that its use may not be as effective when dealing with strongly anisotropic and noncanonical geometries. Our goal here is to extend the plasmonic cloaking technique to irregular obstacles and to show that proper cloak design may provide a significant and uniform scattering reduction, independent of angle of incidence, position, and polarization of the illumination. We investigate how the volumetric effect of scattering cancellation provided by plasmonic media may drastically suppress the scattering for these irregular geometries independent of the illumination angle, and we shed some light on the physical mechanisms and the design rules at the basis of this cloaking technique when applied to objects whose scattering properties are dependent upon polarization and angle of incidence.

In this contribution, we practically show the use of “antiphase” plasmonic scatterers to effectively reduce the scattering cross-section of a cylindrical dielectric object in the visible regime. By properly distributing a set of silver rods around a cylindrical inner core of silica, we demonstrate through a set of full-wave simulations the possibility to obtain a sensible reduction of the scattering phenomenon, achieving a condition of transparency for the structure.

In this contribution, we present the employment of a Genetic Algorithm (GA) based procedure to retrieve the effective permittivity and permeability of planar metamaterial samples. The approach used here is the same of standard Transmission/Reflection (TR) techniques, consisting in extrapolating the sample properties by inversion of its scattering coefficients. The proposed procedure makes use of parametric models for describing the inherently dispersive behavior of the involved materials. This approach eliminates the anomalous behavior of most of the commonly used inversion techniques, providing a consistent representation of the material in the working frequency range. The transition to bulk effective parameters is also investigated determining a proper sample thickness assuring the validation of the homogenization procedure.

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.