Mário G. Silveirinha

Epsilon-near-zero metamaterials and electromagnetic sources: Tailoring the radiation phase pattern

In this work, we investigate the response of epsilon-near-zero metamaterials and plasmonic materials to electromagnetic source excitation. The use of these media for tailoring the phase of radiation pattern of arbitrary sources is proposed and analyzed numerically and analytically for some canonical geometries. In particular, the possibility of employing planar layers, cylindrical shells, or other more complex shapes made of such materials in order to isolate two regions of space and to tailor the phase pattern in one region, fairly independent of the excitation shape present in the other region, is demonstrated with theoretical arguments and some numerical examples. Physical insights into the phenomenon are also presented and discussed together with potential applications of the phenomenon.

Electromagnetic Characterization of Textured Surfaces Formed by Metallic Pins

We develop a homogenization model to characterize textured surfaces formed by a periodic arrangement of thin metallic pins attached to a conducting ground plane: the ldquoFakirs bed of nailsrdquo substrate. It is demonstrated that the textured surface can be accurately modeled using a dielectric function, provided spatial dispersion effects are considered as well as additional boundary conditions. We derive closed analytical formulas for the reflection coefficient, and for the dispersion characteristic of the surfaces waves. In addition, it is demonstrated that the artificial substrate may mimic almost exactly the behavior of an ideal impedance surface boundary, and that the only physical factor that may limit this remarkable property is the skin depth of the metal. The reported results are supported by full wave simulations as well as by experimental data.

Design of matched zero-index metamaterials using nonmagnetic inclusions in epsilon-near-zero media

In this work, we study the electrodynamics of metamaterials that consist of resonant non-magnetic inclusions embedded in an epsilon-near-zero (ENZ) host medium. It is shown that the inclusions can be designed in such a way that both the effective permittivity and permeability of the composite structure are simultaneously zero. Two different metamaterial configurations are studied and analyzed in detail. For a particular class of problems, it is analytically proven that such matched zero-index metamaterials may help improving the transmission through a waveguide bend, and that the scattering parameters may be completely independent of the specific arrangement of the inclusions and of the granularity of the crystal. The proposed concepts are numerically demonstrated at microwaves with a metamaterial realistic realization based on an artificial plasma.

Metamaterial homogenization approach with application to the characterization of microstructured composites with negative parameters

In this work, we develop a systematic and self-consistent approach to homogenize arbitrary nonmagnetic periodic metamaterials. The proposed method does not rely on the solution of an eigenvalue problem and can fully characterize the effects of frequency dispersion, magnetoelectric 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.

Subwavelength 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

Nonlocal homogenization model for a periodic array of ∈-negative rods

\lambda/10

Homogenization of 3-D-connected and nonconnected wire metamaterials

resolution by silver rods at 30 THz is demonstrated numerically using full-wave electromagnetic simulator.

Resolution of subwavelength transmission devices formed by a wire medium.

We propose an effective permittivity model to homogenize an array of long thin epsilon-negative rods arranged in a periodic lattice. It is proven that the effect of spatial dispersion in this electromagnetic crystal cannot be neglected, and that the medium supports dispersionless modes that guide the energy along the rod axes. It is suggested that this effect may be used to achieve subwavelength imaging at the infrared and optical domains. The reflection problem is studied in detail for the case in which the rods are parallel to the interfaces. Full wave numerical simulations demonstrate the validity and accuracy of the new model.

Additional boundary condition for the wire medium

The homogenization of composite structures made of long thin metallic wires is an important problem in electromagnetics because they are one of the basic components of the double-negative medium. In this paper, we propose a new analytical model to characterize the effective permittivity of the three-dimensional-wire medium in the long wavelength limit. We study two different topologies for the wire medium. The first structure consists of a lattice of connected wires, whereas the second one consists of a lattice in which the wires are not connected. Our results show that the propagation of electromagnetic waves in the two metamaterials is very different. While one of the structures exhibits strong spatial dispersion, the other one seems to be a good candidate for important metamaterial applications. We also found that, for extremely low frequencies, one of the structures supports modes with hyperbolic wave normal contours, originating negative refraction at an interface with air. We validated our theoretical results with numerical simulations.

Nonlocal permittivity from a quasistatic model for a class of wire media

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 subwavelength 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 subwavelength resolution to practically arbitrary distances.