1,721,054 research outputs found
Exploiting the surface dispersion of nanoparticles to design optical-resistive sheets and Salisbury absorbers
No full textIn this Letter, we propose a method to implement resistive sheets exhibiting a desired value of the intrinsic surface resistance at optical frequencies. Considering the sheet made by arrays of plasmonic nanoparticles, the idea is to tailor the surface dispersion occurring when the dimensions of the nanoparticles are smaller than the mean free path of electrons in the constituent material. An analytical model of the surface resistance is proposed and its effectiveness assessed through full-wave simulations. Finally, the applicability of the proposed resistive sheets to implement optical Salisbury screens is discussed and validated through full-wave simulations
Design and applications of spatially-dispersive phase-gradient metasurfaces
No full textIn this work, we explore the design of spatially-dispersive gradient metasurfaces able exhibiting different phase profiles as the angle of incidence changes. Differently from earlier designs, characterized by an intrinsically-weak spatial-dispersion, here the angular selectivity of the individual Huygens cells composing the metasurface is intentionally enhanced and optimized. With a combination of analytical and numerical results, it is shown that such optimized devices exhibit different macroscopic behaviors vs. the incidence angle and offer additional possibilities compared to conventional gradient metasurfaces in many relevant applicative scenarios
Optical scattering cancellation through arrays of plasmonic nanoparticles: A review
No full textIn this contribution, we review and discuss our recent results on the design of
optical scattering cancellation devices based on an array of plasmonic nanoparticles.
Starting from two different analytical models available to describe its electromagnetic
behavior, we show that a properly designed array of plasmonic nanoparticles behaves both
as an epsilon-near-zero metamaterial and as a reactive metasurface and, therefore, can be
successfully used to reduce the optical scattering of a subwavelength object. Three different
typologies of nanoparticle arrays are analyzed: spherical, core-shell and ellipsoidal
nanoparticles. We prove, both theoretically and through full-wave simulations, that such
nanostructures can be successfully used as a cloaking device at ultraviolet and optical
frequencies
Design of a non-Foster actively loaded SRR and application in metamaterial-inspired components
No full textIn this paper, we investigate on the use of non-Foster active elements to increase the operation bandwidth of a split-ring resonator (SRR) for possible application in metamaterial-inspired components. First, we design the circuit topology of the active load required to compensate the intrinsic reactance of the SRR and get a broadband response. Then, we show that the same procedure can be successfully applied to the case of a SRR-based monopole antenna and, in principle, to any metamaterial-inspired device employing SRRs. Finally, integrating an electromagnetic and a circuit simulator, we propose a possible realistic implementation of the active load, based on the employment of commercially available circuit elements. The obtained results (seven times improvement of the impedance bandwidth of the SRR-based monopole antenna) prove that non-Foster active loads can be successfully used to overcome the inherent narrow-band operation of SRR-based passive metamaterials and metamaterial-inspired components. The implementation issues related to circuit element dispersion, parasitic effects, and stability of the active circuit are fully considered in the proposed design
Some applications of MTMs based on non-Foster active loads
No full text""In this contribution, we propose a novel approach to dramatically improve the operation bandwidth of a Split Ring Resonator (SRR) by loading its external gap with an active non-Foster circuit. The theoretical aspects, as well as some applications in the field of electrically small microwave antennas, enhanced microwave transmission, and microwave absorbers are presented. "
Possible implementation of epsilon-near-zero metamaterials working at optical frequencies
No full textMetamaterials (MTMs) exhibiting a near-zero real part of the permittivity function in a given frequency range have been demonstrated to be useful in several application fields, including field localization and focusing. So far, however, the realistic implementations of such materials working at optical frequencies and exhibiting a reasonable level of losses are rare. In this work, we propose a possible implementation of optical epsilon-near-zero (ENZ) MTMs based on the employment of an array of core-shell nano-spheres embedded in a dielectric medium. The core of the nano-spheres and the host medium are both made of silica, while the shell is formed by a plasmonic material (i.e. silver). Using classical homogenization formulas, we show that it is possible to design the array in such a way to exhibit near-zero values of the effective real permittivity with relatively low losses at optical frequencies. These results are supported and confirmed by proper full-wave simulations and design examples
Optical cloaking of cylindrical objects by using covers made of core-shell nano-particles
No full textIn this Letter, we propose an engineered design of optical cloaks based on the scattering cancellation technique and intended to reduce the observability of cylindrical objects. The cover, consisting of a periodic arrangement of core–shell nanospheres, is designed in such a way to exhibit near-zero values of the real part of the homogenized effective permittivity at optical frequencies. Full-wave numerical simulations, considering the measured data of the dielectric function of the plasmonic material composing the shell, show that the cloak is able to reduce by about 6 dB the scattering cross section of a finite-length cylinder at around 740 THz with a −3 dB fractional bandwidth of about 7%. We show also that this result is not significantly affected by the perturbation of the periodic alignment of the core–shell nanospheres, due to possible fabrication issues or to an amorphous arrangement
Metasurface Mantle Cloak for Antenna Applications
No full text"In this work, we exploit the mantle cloak technique to minimize the scattering of a receiving electric dipole antenna at its resonance frequency. Theoretical limitations of the proposed setup are analyzed. Furthermore, we show how our approach can be successfully used to dramatically reduce the blockage effects between two electrically close dipole antennas. All the results are validated by the means of full-wave numerical simulations.
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