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Mario G. Silveirinha

Publications and source records attributed to Mario G. Silveirinha.

49 records · Page 3Linked to original sources
arXiv2012

Finite-difference frequency-domain method for the extraction of effective parameters of metamaterials

Here, we report a numerical implementation of the nonlocal homogenization approach recently proposed in [M. Silveirinha, Phys. Rev. B 75, 115104 (2007)], using the finite difference frequency-domain method to discretize the Maxwell-Equations. We apply the developed formalism to characterize the nonlocal dielectric function of several structured materials formed by dielectric and metallic particles, and in particular, we extract the local permittivity, permeability and magnetoelectric coupling parameters when these are meaningful. It is shown that the finite differences frequency domain implementation of the homogenization method is stable and robust, yielding very accurate results.

cond-mat.mtrl-sci↗
arXiv2012

Radiation from elementary sources in a uniaxial wire medium

We investigate the radiation properties of two types of elementary sources embedded in a uniaxial wire medium: a short dipole parallel to the wires and a lumped voltage source connected across a gap in a generic metallic wire. It is demonstrated that the radiation pattern of these elementary sources have quite anomalous and unusual properties. Specifically, the radiation pattern of a short vertical dipole resembles that of an isotropic radiator close to the effective plasma frequency of the wire medium, whereas the radiation from the lumped voltage generator is characterized by an infinite directivity and a non-diffractive far-field distribution.

physics.class-ph↗
arXiv2011

Sampling and Squeezing Electromagnetic Waves through Subwavelength Ultranarrow Regions or Openings

Here, we investigate the physical mechanisms that may enable squeezing a complex electromagnetic field distribution through a narrow and/or partially obstructed region with little amplitude and phase distortions. Following our recent works, such field manipulations may be made possible by a procedure in which the incoming wave is first "sampled" "pixel by pixel" using an array of metallic waveguides, and in a second step the energy corresponding to each individual pixel is "squeezed" through a very narrow channel filled with a permittivity-near zero material. In this work, we study in detail these processes in scenarios where the electromagnetic wave is compressed along a single direction of space, and present theoretical models that enable the analytical modeling of such phenomena. Full-wave results obtained with an electromagnetic simulator, demonstrate the possibility of compressing an incoming wave several folds through ultranarrow channels filled with silicon carbide. The "sampling and squeezing" concept may enable unparalleled control of electromagnetic waves in the nanoscale.

cond-mat.mtrl-sci↗
arXiv2008

Transmission-Line Analysis of Epsilon-Near-Zero (ENZ)-Filled Narrow Channels

Following our recent interest in metamaterial-based devices supporting resonant tunneling, energy squeezing and supercoupling through narrow waveguide channels and bends, here we analyze the fundamental physical mechanisms behind this phenomenon using a transmission-line model. These theoretical findings extend our theory, allowing us to take fully into account frequency dispersion and losses and revealing the substantial differences between this unique tunneling phenomenon and higher-frequency Fabry-Perot resonances. Moreover, they represent the foundations for other possibilities to realize tunneling through arbitrary waveguide bends, both in E and H planes of polarization, waveguide connections and sharp abruptions and to obtain analogous effects with geometries arguably simpler to realize.

cond-mat.mtrl-sci↗
arXiv2008

Reflectionless Sharp Bends and Corners in Waveguides Using Epsilon-Near-Zero Effects

Following our recent theoretical and experimental results that show how zero-permittivity metamaterials may provide anomalous tunneling and energy squeezing through ultranarrow waveguide channels, here we report an experimental investigation of the bending features relative to this counterintuitive resonant effect. We generate the required effectively-zero permittivity using a waveguide operating at the cut-off of its dominant mode, and we show how sharp and narrow bends may be inserted within the propagation channel without causing any sensible reflection or loss.

cond-mat.mtrl-sci↗
arXiv2007

Additional Boundary Condition for a Wire Medium Connected to a Metallic Surface

In this work, we demonstrate that the interaction of electromagnetic waves with a microstructured material formed by metallic wires connected to a metallic surface can be described using homogenization methods provided an additional boundary condition is considered. The additional boundary condition is derived by taking into account the specific microstructure of the wire medium. To illustrate the application of the result, we characterize a substrate formed by an array of tilted metallic wires connected to a ground plane, demonstrating that in such configuration the wire medium behaves essentially as a material with extreme optical anisotropy and that in some circumstances the substrate can be seen as an impedance surface.

cond-mat.mtrl-sci↗
arXiv2007

Nanoinsulators and nanoconnectors for optical nanocircuits

Following our recent idea of using plasmonic and non-plasmonic nanoparticles as nanoinductors and nanocapacitors in the infrared and optical domains [N. Engheta, A. Salandrino, and A. Alu, Phys. Rev. Letts., Vol. 95, 095504, (2005)], in this work we analyze in detail some complex circuit configurations involving series and parallel combinations of these lumped nanocircuit elements at optical frequencies. Using numerical simulations, it is demonstrated that, after a proper design, the behavior of these nanoelements may closely mimic that of their lower frequency (i.e., radio frequency (RF) and microwave) counterparts, even in relatively complex configurations. In addition, we analyze here in detail the concepts of nanoinsulators and nanoconnectors in the optical domain, demonstrating how these components may be crucial in minimizing the coupling between adjacent optical nanocircuit elements and in properly connecting different branches of the nanocircuit. The unit nanomodules for lumped nanoelements are introduced as building blocks for more complex nanocircuits at optical frequencies. Numerical simulations of some complex circuit scenarios considering the frequency response of these nanocircuits are presented and discussed in details, showing how practical applications of such optical nanocircuit concepts may indeed be feasible within the current limits of nanotechnology.

cond-mat.mtrl-sci↗
arXiv2007

A Metamaterial Homogenization Approach with Application to the Characterization of Microstructured Composites with Negative Parameters

In this work, we develop a new systematic and self-consistent approach to homogenize arbitrary non-magnetic periodic metamaterials. The proposed method does not rely on the solution of an eigenvalue problem and can fully characterize the effects of frequency dispersion, magneto-electric coupling, and spatial dispersion, even in frequency band-gaps or when the materials are lossy. We formulate a homogenization problem to characterize a generic microstructured artificial material, and demonstrate that it is equivalent to an integral-differential system. We prove that this complex system can be reduced to a standard integral equation and solved using standard methods. To illustrate the application of the proposed method, we homogenize several important metamaterial configurations involving split ring resonators and metallic wires.

cond-mat.mtrl-sci↗
arXiv2007

Design of Linear-to-Circular Polarization Transformers Made of Long Densely Packed Metallic Helices

In this work, we study the realization of realistic polarization transformers formed by long metallic helices. To this end, we propose a new homogenization model to characterize the propagation of electromagnetic waves in medium formed by infinitely long helices. We derive approximate analytical expressions for the effective permittivity, effective permeability and the magnetoelectric tensor of the composite material, taking into account the effects of spatial dispersion. We apply the new homogenization model to characterize novel linear-to-circular polarization transformers. Our results show that the metamaterial screen may be designed in such a way that an incoming linearly polarized wave may be transformed into a circularly polarized transmitted wave, and that the transmission efficiency of such polarization transformer may be as high as 95%. The theoretical results are supported by full wave simulations.

cond-mat.mtrl-sci↗
arXiv2006

Additional Boundary Condition for the Wire Medium

In this paper, it is proved that the continuity of the tangential components of the average electric and magnetic fields is insufficient to describe the reflection of plane waves by a set of thin parallel wires embedded in a dielectric host using a homogenization approach. It is shown that an additional boundary condition is required to conveniently model a slab of the homogenized metamaterial. In order to understand how the different electromagnetic modes are excited at the interface, the problem of reflection of a plane wave by a set of semi-infinite parallel wires is solved analytically within the thin-wire approximation. Based on the derived result and other arguments, a new boundary condition is proposed for the homogenized wire medium. Extensive numerical simulations support our theoretical analysis, and show that when the additional boundary condition is considered the agreement between full wave results and homogenization theory is very good even for wavelengths comparable with the lattice constant.

cond-mat.mtrl-sci↗
arXiv2006

Sub-wavelength imaging at infrared frequencies using an array of metallic nanorods

We demonstrate that an array of metallic nanorods enables sub-wavelength (near-field) imaging at infrared frequencies. Using an homogenization approach, it is theoretically proved that under certain conditions the incoming radiation can be transmitted by the array of nanorods over a significant distance with fairly low attenuation. The propagation mechanism does not involve a resonance of material parameters and thus the resolution is not strongly affected by material losses and has wide bandwidth. The sub-wavelength imaging with $λ/10$ resolution by silver rods at 30 THz is demonstrated numerically using full-wave electromagnetic simulator.

cond-mat.mtrl-sci↗
arXiv2006

Resolution of sub-wavelength lenses formed by the wire medium

The restrictions on the resolution of transmission devices formed by wire media (arrays of conductive cylinders) recently proposed in [Phys. Rev. B, 71, 193105 (2005)] and experimentally tested in [Phys. Rev. B, 73, 033108 (2006)] are studied in this paper using both analytical and numerical modeling. It is demonstrated that such transmission devices have sub-wavelength resolution that can in principle be made as fine as required by a specific application by controlling the lattice constant of the wire medium. This confirms that slabs of the wire medium are unique imaging devices at the microwave frequency range, and are capable of transmitting distributions of TM-polarized electric fields with nearly unlimited sub-wavelength resolution to practically arbitrary distances.

physics.optics↗