Showing papers on "Metamaterial cloaking published in 2005"

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.

Multifocal flat lens with left-handed metamaterial

Abstract: We show experimental results demonstrating multiple focal lengths at microwave frequencies in a flat lens constructed of left-handed metamaterial (LHM). In contrast to conventional lenses, which are constructed of materials with positive index and require a curved surface or inhomogeneous structures to focus light or other electromagnetic radiation, no curvature is needed with a LHM because of a negative effective index of refraction. Such a flat lens has the advantage of being capable of changing the focal length by simply changing the distance between the electromagnetic source and the lens.

Electromagnetic wave propagation in anisotropic metamaterials created by a set of periodic inductor-capacitor circuit networks

Abstract: We propose a complete set of periodic circuit networks which can realize electromagnetic wave propagation in different two-dimensional (2D) isotropic and anisotropic metamaterials (AMMs). We synthesize the periodic circuits with unit cells of series capacitor or inductor in orthogonal directions, together with either capacitor or inductor shunted to ground. The dispersion relations of the periodic circuits are derived by applying Bloch boundary conditions to the unit cell, which show either elliptic or hyperbolic dispersion surface in phase space. The effective constitutive parameters are obtained by choosing different types and values of the impedance elements in the unit cell. The validity of the circuit models is proved by showing examples that the anisotropic $L\text{\ensuremath{-}}C$ circuits could exhibit the wave propagation characteristics of two 2D AMMs with different cutoff properties, called never-cutoff or anti-cutoff medium. We construct interfaces between isotropic normal medium and AMMs with properly designed $L\text{\ensuremath{-}}C$ circuits and analyze the electromagnetic wave propagation using microwave circuit simulations. We demonstrate extraordinary electromagnetic wave reflection and refraction phenomena including negative refraction, total reflection with reversion of the critical angle and anomalous Brewster effect that have good agreements with the theoretical analysis. Furthermore, we show that the $L\text{\ensuremath{-}}C$ circuit models of AMMs could lead to different approach of actual implementation of 2D AMMs through capacitance loaded transmission line metamaterials. The simulation on actual microstrip line structure demonstrates similar wave propagation phenomena of AMMs, and the losses in the structure only affect the magnitude of the propagating energy.

Relationship between quantum two-photon correlation and classical spectrum of light

Abstract: We show that the two-photon temporal (longitudinal) correlation of light is limited by its classical optical spectral width. We present examples of the sources of two-photon light approaching this limit.

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 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.

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.

Application and research of harmonic diffractive/refractive optics in visible spectrum

Abstract: Many optical systems used in the infrared spectrum have, so far, adopted binary optical elements (BOE) to achieve a better performance. Especially, in the middle and long infrared spectrum, binary optical elements are commonly used. Thus, limited by the manufacture technology, the applications of binary optics in the visible spectrum are rare. This tentative research aims at finding the practicability of applying BOEs in the visible spectrum. We attempted to replace the reference lens group in the interferometer with a harmonic diffractive/refractive hybrid lens group, expecting that the wave aberration be well-corrected. In this paper, the main procedure of designing a hybrid optical system is introduced with an example of “F2” lens group. After the analysis on the interference pattern and wave front, the comparison between the tested result and theoretical result can be made. It demonstrates that the hybrid optical system is capable of being applied in the visible spectrum. The analysis also discloses that raising the diffractive efficiency is the next step for us to take.

Simulation of interaction of the electromagnetic radiation in the form of surface wave with the solid surfaces

Abstract: Interaction of electromagnetic wave by solid surface is interesting for creating a new generation of the technical devices, which can be to use both in optics for creating of optics and systems of new generation and with the creation of new type computers. There is interest in the simulation of interaction of electromagnetic radiation with the surfaces of different materials with the purpose of selecting of stated problems most suitable for the solution.

The RF spectrum of partially polarized light and its application to system characterization

Abstract: Formalism for complete characterization of the RF spectrum of partially polarized light is described The formalism is used to characterize the polarization dependence of the RF spectrum at the output of a PMD/PDL medium

Waveguides based on High Refractive Index Metamaterials

Abstract: We recently discovered that metallic films with a sub-wavelength periodic arrangement of nano-slits act as dielectric slabs with an arbitrary high refractive index controlled by geometry only. Here, we investigate waveguides based on these metamaterials.

Negative Refraction in the IR and Visible Frequencies

Abstract: Here we give a brief overview of our theoretical work in the area of metamaterials with negative refraction at the infrared (IR) and visible frequencies. We will provide physical insights and intuitive remarks into our findings

Multi-band sub wavelength magnetic reflectors based on spiral

Abstract: We report our experimental and theoretical studies on a metamaterials consisting of a metallic planar spiral with a metallic ground separated by a thin dielectric layer. We show that this structure, which is of isotropic with multi-band, can reflect electromagnetic wave in-phase at a series of frequencies and of subwavelength size at some lower resonance frequencies. This phenomenon is mainly governed by a series of holistic magnetic resonances.