Showing papers on "Transformation optics published in 2004"

Robust method to retrieve the constitutive effective parameters of metamaterials.

Abstract: We propose an improved method to retrieve the effective constitutive parameters (permittivity and permeability) of a slab of metamaterial from the measurement of S parameters. Improvements over existing methods include the determination of the first boundary and the thickness of the effective slab, the selection of the correct sign of effective impedance, and a mathematical method to choose the correct branch of the real part of the refractive index. The sensitivity of the effective constitutive parameters to the accuracy of the S parameters is also discussed. The method has been applied to various metamaterials and the successful retrieval results prove its effectiveness and robustness.

Enhancement of evanescent waves in waveguides using metamaterials of negative permittivity and permeability

Abstract: Electromagnetic waves in waveguides consisting of metamaterials with negative permittivity and permeability are analyzed. It is found that metamaterials can enhance the intensity of the evanescent waves in the cladding without altering the propagation constant of the waveguide for both TE and TM modes. This is a unique property of metamaterials. The enhancement factor increases with the increasing of the thickness of the metamaterial and saturates when complete surface polaritons were established at the interface between the metamaterial and the cladding. The enhancement effect can improve the performance of evanescent-wave-based waveguide devices.

A novel dispersive FDTD formulation for modeling transient propagation in chiral metamaterials

Abstract: Chiral media engineered for applications at microwave frequencies can be described as metamaterials composed of randomly oriented helices (with sizes typically less than a wavelength) embedded within an achiral background that is characterized by its permittivity and permeability. Chiral metamaterials embody properties of magnetoelectric coupling and polarization rotation. Chiral media are also highly dispersive and no effective full-wave time domain formulation has been available to simulate transient propagation through such an important class of metamaterials. A new finite-difference time-domain (FDTD) technique is introduced in this paper to model the interaction of an electromagnetic wave with isotropic dispersive chiral metamaterials, based on the implementation of a wavefield decomposition technique in conjunction with the piecewise-linear recursive convolution method. This formulation represents the first of its kind in the FDTD community. The FDTD model is validated by considering a one-dimensional example and comparing the simulations with available analytical results. Moreover, the FDTD technique is also used to investigate the propagation of electromagnetic waves through multilayered metamaterial slabs that include dispersive chiral and double-negative media. Hence, this model enables the investigation of complex dispersive metamaterials with magnetoelectric coupling and double-negative behavior as well as facilitates the exploitation of their unique properties for a variety of possible applications.

Leaky-wave radiation from planar negative-refractive-index transmission-line metamaterials

Abstract: This paper examines the radiation properties of one- and two-dimensional transmission-line negative-refractive-index (NRI) metamaterial antennas, and highlights the critical features of their dispersion characteristics as they pertain to leaky-wave radiation. This permits an explanation of the mechanisms with which backward, broadside or forward beams can be obtained from NRI transmission-line metamaterials. This discussion is supported by numerical simulations as well as by experimental results.

Radiation characteristics of an infinite line source surrounded by concentric shells of metamaterials

Abstract: This paper presents an analytical study on the effect of concentric circular shells of metamaterials on the radiation properties of an infinite line source. The results show that with proper design, it is possible to increase the gain of the line source when surrounded by cylindrical shells of metamaterials, relative to the case where the line source is surrounded by free space.

Oblique plane wave scattering by an array of dielectric and metamaterial cylinders

Abstract: The influence of negative permittivity and permeability on the scattering patterns for dielectric and metamaterial posts is presented. Combination of an extended iterative scattering procedure and the orthogonal expansion method is used to investigate oblique scattering of an electromagnetic plane wave from an arbitrary configuration of parallel circular cylinders.

Determination of effective material parameters for a metamaterial based on analysis of local fields

Abstract: There is considerable interest in the design of metamaterials for specific unusual electromagnetic properties. We want materials with particular values of epsilon and mu that are less than zero. We desired a calculation procedure that could take a geometric structure and evaluate the effective material parameters, both for design validation and in a search for new shapes. There have been other descriptions of similar efforts in the literature; our method is an improvement over the existing methods by reducing the errors due to phase variation across a structure while not requiring a solver that calculates the charge and current directly. We derive general formulas/algorithms for computing effective electric permittivity /spl epsi/(/spl omega/) and magnetic permeability /spl mu/(/spl omega/) for polarizable media from first-principles classical E and M. We apply them to filamentary, conducting structures that are candidates for making double-negative metamaterials. Specifically we show we can analyze specific structures and design a material where /spl epsi/(/spl omega/) and /spl mu/(/spl omega/) are simultaneously negative. We use the split-ring resonators and capacitively-end-loaded linear electric dipoles as examples and show that they form Lorentz materials.

Arrangement for transforming an optical radiation field

Abstract: The invention relates to a system for transforming an optical radiation field propagating in a z direction and comprising a symmetrical beam radiation parameter product in x and y directions into a radiation field having an asymmetrical product of beam parameters by means of a transformation optics, wherein the x, y and z directions forming an orthogonal co-ordinate system. The inventive arrangement is characterised in that the radiation field is first and foremost segmented into at least two partial radiation fields by the transformation optics in the y direction which are afterwards offset in the x direction by the transformation optics, and said partial radiation fields are offset in the y direction by the transformation optics in such a way that the centres of gravity thereof is located on a line which is perpendicular with respect to the line where the centres of gravity of the partial radiation fields are situated before entering the transformation optics. Said arrangement is also characterised in that the radiation field is first and foremost segmented into at least two partial radiation fields by the transformation optics in the y direction, said transformation optics turns said partial radiation fields to 90° around the axis Z respectively and the partial radiation fields after being exposed to rotation are put together into a line in the direction y.

Diffraction of nonuniform electromagnetic beams at a slab of metamaterial

Abstract: A plane-wave expansion method is used to analyze the interaction of nonuniform electromagnetic waves with a metamaterial slab A network of transmission lines models the propagation of the constituting plane-wave components of the incident and diffracted beams Having determined the complex amplitude of these components, one can obtain the total solution using superposition The obtained simulation results demonstrate the negative refraction phenomenon and focusing effect in a metamaterial slab The results show very good agreement with those reported in the literature using fully numerical methods Since the approach is semi-analytical, it is not only more precise than purely numerical methods, but also demands minor computational resources

Field focusing in the presence of the metamaterial plate

Abstract: Absfmcf The communication deals with the investigation of the electromagnetic radiation focusing Using a plane-parallel plate of a material with negative real parts of the permittivity and permeability. The reasons are demonstrated for the restriction of the limiting attainable resolution of the system. The possibility of obtaining the separated images of sources the distance between which is much less than the wavelength is confirmed theoretically and experimentally.