Showing papers on "Transformation optics published in 2005"

Electromagnetic parameter retrieval from inhomogeneous metamaterials

Abstract: We discuss the validity of standard retrieval methods that assign bulk electromagnetic properties, such as the electric permittivity « and the magnetic permeability m, from calculations of the scattering sSd parameters for finite-thickness samples. S-parameter retrieval methods have recently become the principal means of characterizing artificially structured metamaterials, which, by nature, are inherently inhomogeneous. While the unit cell of a metamaterial can be made considerably smaller than the free space wavelength, there remains a significant variation of the phase across the unit cell at operational frequencies in nearly all metamaterial structures reported to date. In this respect, metamaterials do not rigorously satisfy an effective medium limit and are closer conceptually to photonic crystals. Nevertheless, we show here that a modification of the standard S-parameter retrieval procedure yields physically reasonable values for the retrieved electromagnetic parameters, even when there is significant inhomogeneity within the unit cell of the structure. We thus distinguish a metamaterial regime, as opposed to the effective medium or photonic crystal regimes, in which a refractive index can be rigorously established but where the wave impedance can only be approximately defined. We present numerical simulations on typical metamaterial structures to illustrate the modified retrieval algorithm and the impact on the retrieved material parameters. We find that no changes to the standard retrieval procedures are necessary when the inhomogeneous unit cell is symmetric along the propagation axis; however, when the unit cell does not possess this symmetry, a modified procedure—in which a periodic structure is assumed—is required to obtain meaningful electromagnetic material parameters. DOI: 10.1103/PhysRevE.71.036617

Electromagnetic surface modes in structured perfect-conductor surfaces.

Abstract: Surface-bound modes in metamaterials forged by drilling periodic hole arrays in perfect-conductor surfaces are investigated by means of both analytical techniques and rigorous numerical solution of Maxwell's equations. It is shown that these metamaterials cannot be described in general by local, frequency-dependent permittivities and permeabilities for small periods compared to the wavelength, except in certain limiting cases that are discussed in detail. New related metamaterials are shown to exhibit exciting optical properties that are elucidated in the light of our simple analytical approach.

A brief intro to metamaterials

Abstract: Metamaterials are new artificial materials with unusual electromagnetic properties that are not found in naturally occurring materials. All "natural" materials such as glass, diamond and such have positive electrical permittivity, magnetic permeability and an index of refraction. In these new artificially fabricated materials - termed as negative index materials (NIM) or double negative (ONG) media or left handed (LH) materials or backward wave (BW) media - all these material parameters are negative. With these unusual material parameters, new kinds of miniaturized antennas and microwave components/devices can be created for the wireless communications and the defense industries. The electrical permittivity and the magnetic permeability are the main determinants of a material's response to electromagnetic (EM) waves. In metamaterials, both these material parameters are negative. Correspondingly, the refractive index of the metamaterials is also negative. Another strange property of metamaterials is its reverse Doppler effect.

Effective parameters of resonant negative refractive index metamaterials : interpretation and validity

Abstract: We present a numerical study of resonant negative refractive index (NRI) metamaterials in which their effective parameters are calculated. For a periodic media consisting of split-ring resonators and metallic wires the effective refractive index is compared by means of two different methods. The first one is an inversion procedure in which the effective refractive index is calculated from the reflection and transmission coefficients of a finite structure and the second one consists its calculation from the phase velocity issued from the dispersion diagram. A significant difference between the two cases is highlighted in the frequency interval of interest (NRI regime) and for the finite media, counterintuitive observations are made. These anomalous features are observed in a frequency range in which there is a non-negligible contribution of the higher-order modes to propagation inside the periodic metamaterial. Hence in this particular frequency interval, the media cannot be described by an effective refractive index in a Fresnel sense. In other frequency regions, both methods converge and it will be shown that the metamaterial exhibits a negative refractive index.

Linear and Nonlinear Homogenized Composite Mediums as Metamaterials

Abstract: Metamaterials are artificial composites which are characterized by physical properties that are not possessed, either to the same extent or at all, by their component phases. Homogenization provides a means of conceptualizing such metamaterials. The constitutive parameters of homogenized composite mediums (HCMs) may be estimated through the implementation of well-established homogenization formalisms. In particular, those of Maxwell Garnett and Bruggeman, as well as the more comprehensive strong-property-fluctuation theory, are discussed here in the context of HCM metamaterials. We present a survey of five generic examples of metamaterials; each example is envisaged as an HCM. The unusual structures and properties of these HCM metamaterials are emphasized. First, we examine bianisotropic HCMs as metamaterials. While bianisotropy is rarely observed in naturally occurring materials, bianisotropic HCMs may be readily conceptualized. Second, an anomalous form of plane wave propagation known as Voigt wave prop...

Topology and Design of Wide-Band 3D Metamaterials made of Periodically Loaded Transmission Line Arrays

Abstract: We propose a new topology for realizing artificial microwave materials that exhibit a negative refractive index over a wide frequency band. These metamaterials consist of a three-dimensional transmission line mesh that is loaded with reactive series and shunt elements to create negative permittivity and permeability. The cubic-cell transmission line host network is a physical realization of the 3D distributed node TLM lattice which has the same low-frequency properties as the FDTD Yee scheme. This paper describes the topology, the theory, the design, and possible realizations of such a metamaterial. Its wave properties are validated by full-wave simulations using the time domain electromagnetic field simulation tool MEFiSTo-3D Pro.

Birefringent left-handed metamaterials and perfect lenses for vectorial fields

Abstract: We describe the properties of specific non-reflecting birefringent left-handed metamaterials and demonstrate a birefringent perfect lens for vectorial fields. We predict that, in a sharp contrast to the concept of a conventional perfect lens realized at = μ = −1 (where is the dielectric permittivity and μ is the magnetic permeability), the birefringent left-handed slab possesses the property of negative refraction either for TE- or TM-polarized waves or for both of them simultaneously. This allows selective focusing and a spatial separation of the images created at different polarizations. We discuss several applications of the birefringent left-handed lenses such as the beam splitting and near-field diagnostics at the sub-wavelength scale.

Nonlinear left-handed metamaterials

Abstract: [1] We analyze nonlinear properties of microstructured materials with the negative refractive index, the so-called left-handed metamaterials. We demonstrate that the hysteresis-type dependence of the magnetic permeability on the field intensity allows changing the material properties from left to right handed and back. Using the finite difference time domain simulations, we study the wave reflection from a slab of a nonlinear left-handed material and observe generation and propagation of temporal solitons in such materials. We demonstrate also that the nonlinear left-handed metamaterials can support both transverse electric– and transverse magnetic–polarized self-trapped localized beams, spatial electromagnetic solitons. Such solitons appear as single-hump and multihump beams, being either symmetric or antisymmetric, and they can exist because of the hysteresis-type magnetic nonlinearity and the effective domains of negative magnetic permeability.

Enabling RF/microwave devices using negative-refractive-index transmission-line metamaterials

Abstract: Metamaterials are artificially engineered structures with unusual electromagnetic properties. In this article, we review the implementation of isotropic metamaterials that exhibit a negative permittivity and a negative permeability, thus leading to a negative index of refraction. Specifically, the article focuses on transmission-line metamaterials, which are planar structures comprising a network of distributed transmission lines loaded periodically in a dual (high-pass) configuration with lumped inductors, L, and capacitors, C. The periodic unit cell is much smaller than the wavelength, thus leading to an effective medium in which the lumped loading elements can be either chip or printed. Based on this transmission-line method, a number of RF/microwave devices are presented, including lenses that can overcome the diffraction limit, compact phase-shifting lines, small antennas, antenna feed networks and baluns, backward leaky-wave antennas and high-directivity coupled-line couplers.

Compact leaky-wave components using metamaterial bilayers

Abstract: Here we propose and analyze theoretically the use of metamaterial planar layers for synthesizing compact sub-wavelength leaky-wave radiators in the microwave regime. In particular, the possibility of pairing "conjugate" metamaterials in order to squeeze the dimensions of microwave components is explored here for the leaky-wave operation of an open waveguide consisting of a stack of grounded metamaterial layers. We show the salient guidance and radiation properties of the anomalous natural modes supported by these bilayered structures, giving further physical insights into the phenomenon.

Electromagnetic response of the split-ring resonator placed inside a waveguide

Abstract: The EM response of split ring resonators, conventionally employed to design the left-handed metamaterials, was studied by modeling the behavior of one ring located in a standard waveguide. It was shown that, besides the expected half and full-wavelength resonances, an additional resonance is excited in the SRR at an intermediate frequency due to coupling between the SRR and the waveguide. This resonance supports longitudinal mode in the waveguide and magnetic dipole-type fields near the SRR. While the response of the SRR at the first resonance can be described by negative permeability, the full-wavelength resonance features negative permittivity and the intermediate resonance exhibits more complex behaviors of the constitutive parameters. The properties of this resonance could be used to design novel metamaterials.

Applications of metamaterials to realize efficient electrically small antennas

Abstract: Metamaterials are engineered media whose electromagnetic responses are different from those of their constituent components. They are often generated by incorporating in a periodic manner various types of artificially fabricated, extrinsic, low dimensional inhomogeneities in some background substrate. Double negative (DNG) metamaterials have both the permittivity and permeability negative. There have been a variety of antenna applications conceived and realized with various types of metamaterials. In this paper, we have investigated the possibility of matching an electrically small electric dipole to free space by surrounding it with a DNG shell. HFSS simulations confirm the resonant power gain predicted analytically and have given us insight into how a realistic electrically small efficient antenna (EESA) could be achieved.

Interactions between electromagnetic waves and elliptically shaped metamaterials

Abstract: The interaction between plane waves and multilayer elliptic cylinders with one or more layers made of metamaterials is considered. An analytical solution is proposed, which extends to double-negative metamaterials an efficient recursive procedure previously developed for double-positive dielectrics. Two cases are considered: multilayer dielectric cylinders and perfectly conducting cylinders with a lossy dielectric coating. Numerical results and comparisons are provided concerning both the internal field and the scattering cross section per unit length, allowing a significant assessment of the scattering properties of metamaterials.

Some Features of the Electrodynamics of Anisotropic Metamaterials

Abstract: We study the features of propagation of electromagnetic wave fields in anisotropic metamaterials composed of lattices of the so-called split-ring resonators embedded in a dielectric substrate. It is shown that strongly slowed waves can exist in such metamaterials if some components of the tensor of effective magnetic permeability are negative. The presence of such waves explains the experimentally observed effect of wave propagation through cutoff waveguides filled with an artificial medium composed of split-ring resonators.

A parallel-grid-enabled variable-mesh FDTD approach for the analysis of slabs of double-negative metamaterials

Abstract: Interesting applications of metamaterials have been proposed in the recent past, and in several cases the use of double-negative (DNG) slabs is appealing. Consequently, a detailed analysis of the propagation of electromagnetic fields inside DNG slabs is critical, and suitable numerical methods are needed. To this aim, a state-of-the-art FDTD approach is here proposed. It is based on a variable-mesh strategy, on the top of a parallel design, compatible with Grid computing technologies. It embeds the Drude model, and a wide variety of sources. Results demonstrate the accuracy and high-performance of the tool, and propose a detailed characterization of DNG slabs.

Features of electrodynamics of fine-structured resonant metamaterials

Abstract: We give a brief review of the state of the art of theoretical and experimental studies in the field of electrodynamics of resonant composite materials (metamaterials) whose dielectric permittivity or magnetic permeability or both can be negative. Principles and methods of realization of such metamaterials in the microwave range, their main distinctive electrodynamic properties, prospects for creating new systems and devices (e.g., more perfect lenses), and ways for moving towards the higher frequencies from microwaves to optics are discussed.

Electromagnetic structures containing negative refractive index metamaterials

Abstract: We review different structures for microwave and optical range containing 'left-handed' metamaterials - artificial composites with simultaneously negative effective permittivity and permeability. Special attention is dedicated to their fundamentals, design strategies and main applications which include subwavelength resonant cavities, superlenses, etc.

Analysis and calculation of effective permittivity for a left-handed metamaterial

Abstract: In this paper, the analytical permittivity models for LH metamaterial are derived using the constitutive relation method and transmission line method, respectively, and the equivalence between these models is investigated. In addition, the validity of these models is proven by numerical simulations. The description of mathematical derivation exhibits clear physical concepts and provides new approaches for better understanding of the negative permittivity effect.

Scattering from multi-layered metamaterials using wave matrices

Abstract: : The complex permittivity (e) and permeability (mu) of a material determine the response of the material to electromagnetic radiation. Usually, the real parts of e and mu are positive for naturally occurring materials at microwave frequencies. Metamaterials are engineered media that are designed to have either a negative permittivity or permeability or both. Negative permeability and negative permittivity would cause electromagnetic waves traveling through this medium to exhibit unusual characteristics such as power flow in a direction opposite to the phase velocity. In this thesis, the wave matrix approach is used to calculate the total reflection and transmission coefficients of a multilayered structure. The method is applicable to all types of materials, including metamaterials. Several layered configurations are studied including both metamaterial and conventional dielectric layers. A MATLAB program is developed to examine the effects of frequency, angle of incidence and polarization. The results are compared to published data. Potential applications of metamaterials are also discussed.

Performance evaluation of 3D FEM-based simulators in modelling scattering problems with metamaterials

Abstract: This contribution is focused on the evaluation of the performances of three-dimensional finite element methods in solving electromagnetic scattering problems involving metamaterials. Finite element methods can be effectively used to provide a convergent approximation for investigating the unusual properties of metamaterials. However, an exhaustive assessment of the performances of the method, both in terms of its accuracy and of the required computational resources, has not been performed yet when metamaterials are involved. This paper addresses this topic by considering the 3D electromagnetic finite element modelling of the scattering properties of simple objects made up of metamaterials.

Planar metamaterials and applications in directive antennas

Abstract: In this paper, we reviewed some recent studies on planar metamaterials and demonstrated two new way to realize high directive antenna for the first time: 1) Quasi-periodic metamaterial surface can suppress transverse-electric (TE) surface waves and support directive emissions 2) Periodic metamaterial surface can be applied in realizing one-dimensional subwavelength Fabry-Perrot (FP) metamaterial cavity which support directive emissions We show both experimentally and theoretically that these phenomena mainly originate from the dispersive reflection phase and surface wave dispersions

Application of hyperbolic dispersion relations of left-handed metamaterials

Abstract: In this paper, we first illustrate the case of a hyperbolic dispersion relation based on two negative constitutive components to predict and experimentally verify the inversion of the critical angle definition Second, hyperbolic dispersion relations with one negative constitutive component are used in the design of a four-port device capable of splitting the incident power into three different outputs as function of frequency

Electrically controllable metamaterials based on 2D wire media

Abstract: Electromagnetic waves in an artificial medium formed by two mutually orthogonal lattices of thin reactively loaded wires (referred to as 2D loaded wire medium (2D LWM)) are considered. In the assumption of a small distance between the loads compared with the wavelength, the loads are taken into account via a distributed surface impedance of the wires. We demonstrate how the directions of phase and group velocities in 2D LWM can be controlled by tunable capacitive loads. Such electrically controllable metamaterials can find applications for example in tunable antenna lenses.

Experimental verification of the characteristic of one-dimensional metamaterials by use of lumped-elements L-C

Abstract: The metamaterials by use of L_C lumped_elements in the transmission line have the preternatural characteristic,which is different from the conventional dielectrics.We report the experimental results in the left_handed range with anti_parallel phase and group velocities in the metamaterials,with the negative refractive index, and we find the bandgap corresponding to zero averaged refractive index.The configuration offers some significant advantages:it is more compact in si ze,the material parameters can be tuned,and the method of fabrication is easy to carried out.

Metamaterial properties, designs, and antenna applications

Abstract: Metamaterials have the potential to allow engineers to tailor the electromagnetic responses of the materials incorporated in antenna systems to enhance their performance. Several examples of the exotic properties of electromagnetic metamaterials will be given. One class of metamaterials that has already demonstrated its usefulness with antennas is the artificial magnetic conductor (AMC). It has been demonstrated that this metamaterial configuration can yield a highly resonant radiating system. The resonances occur for particular combinations of shell sizes and metamaterial properties; they result in significant enhancements of the radiated power. These resonance results have been extended to lossy DNG and epsilon negative (ENG) metamaterials. We have also demonstrated reciprocity between these source results and the scattering of plane waves from the corresponding metamaterial coated spheres. We have shown with HFSS numerical simulations that realistic center-fed electrically small dipole antennas surrounded with an ENG spherical shell and coaxially-fed monopole antennas surrounded with an ENG hemispherical shell can be made to be resonant and matched to an external source. These electrically small antenna systems have very high radiation efficiencies and Q factors near the Chu limit. A review of these metamaterial-based electrically small antenna systems will be presented and current progress toward a proof-of-principle experiment will be discussed

Forward and backward waves in chiral metamaterials

Abstract: In this presentation, we study basic electromagnetic properties of chiral metamaterials, which can have simultaneously negative permittivity and permeability. The reflectivity of a slab filled with a chiral metamaterial, with possibly negative or null constitutive parameters, is analysed and numerical results presented. We consider a monochromatic plane wave propagating in a homogeneous, isotropic medium which illuminates an infinite slab of chiral material. Phenomenon such as electromagnetic propagation in chiral nihility are also discussed.

Birefringent left-handed metamaterials and perfect lenses

Abstract: In this paper, possibilities of wave focussing by a birefringent left-handed lens are discussed. It is shown that such lenses can focus either TE or TM polarized waves or both of them, with a varying distance between TE and TM images, and this property allows expanding the applicability limits of the perfect lenses.