Metamaterials最新文献

We consider such passbands that appear due to excitation of plasmons inside the one-dimensional photonic crystal with elementary cells containing layers of positive and negative permittivities. The corresponding Bloch waves can be regarded as surface plasmon chains that are subsequently excited at the layers’ boundaries. The band structure depends on the elementary cell composition that also determines the plasmon type. The excited plasmons can be similar to surface plasmons that propagate along a dielectric slab “sandwiched” between two semi-spaces with negative permittivity, or to surface plasmons that propagate along a negative permittivity slab sandwiched between two dielectric semi-spaces. It is shown that the existence of negative refraction does not depend on the frequency dispersion of permittivity. The latter fact permits us to distinguish six elementary cell compositions with qualitatively different band structures. The frequency evolution of the band structure of a plasmonic PC with a given frequency dispersion of the permittivity can be considered as a transition between various kinds of band structures.

In this work we provide further advances in the applications of Metamaterial concepts to the classical field of metallic lenses. Some of the limitations that metallic lenses have, such as imperfect matching with free space, can be overcome by Metamaterials, which makes them powerful tools not only in lens field but also in many others. Specifically, our work is devoted to the Extraordinary Transmission Metamaterial because of its low-losses and its potential scaling to any range of the spectrum. Firstly, we explore at the microwave regime the modification of the radiation pattern of a commercial horn antenna when 1 and 4 stacked subwavelength hole arrays are placed as a superstrate. Afterwards, the design of plano- and bi-concave ETM lenses operating at millimetre waves are analysed. Numerical analyses are confirmed by experimental results.

This paper describes an analytical approach to modeling near-field plates, which are non-periodic grating-like structures that can focus electromagnetic waves to subwavelength dimensions. The analysis provides additional insight into the operation and design of such plates that focus cylindrical waves to subwavelength resolutions. Explicit expressions for the current density induced on the plate and its impedance profile are derived. The analytical expressions are validated numerically.

The Swiss Roll structure is a strongly magnetic metamaterial at radiofrequency but is constructed from non-magnetic materials. This makes it an attractive candidate for use in the magnetic resonance environment. In this paper I review the performance of the material with particular emphasis on its imaging capability, and describe how the structure can be tuned to alter its magnetic properties. Its potential for use in MRI is discussed.

We discuss methods for hiding of objects from detection by electromagnetic waves (cloaking), and also ways by which cloaked objects may be detected. The possibility of detection by means of thermal radiation emitted when electromagnetic energy is resonantly absorbed motivates the calculation of local density of states (LDOS), which controls the ability of a source inside a structured system to radiate. We give the first results of an investigation of the LDOS for systems which cloak by resonant interaction with electromagnetic fields.

The majority of the designs of electromagnetic cloaks presented in the current literature require a metamaterial, the relative permittivity and/or permeability of which are smaller than one. Due to basic dispersion constraints, such permittivity (or permeability) can exist only within some restricted frequency band. This fact causes a passive electromagnetic cloak to be an inherently narrowband device. Here, it is shown both numerically and experimentally that the basic dispersion constraints of any passive medium might be overcome by using an active transmission line-based metamaterial. This type of metamaterial appears promising for the design of broadband cloaking devices.

We have designed, fabricated and measured electrically-driven active metamaterials which operate as external modulators for TeraHertz Quantum Cascade Lasers. The modulation is achieved by applying a voltage to the metamaterial layer which actively displaces carriers from the n-doped layer causing changes in damping and frequency location of the lowest metamaterial response. We demonstrate their operation at 2.4 and 2.8 TeraHertz and obtain a maximum modulation depth of ∼60% with a large degree of modulation linearity.

In this work, we numerically demonstrate electromagnetic focusing using a spatially dispersive metamaterial. Based on the phenomenon of broadband all-angle negative refraction by a crossed wire mesh, it is demonstrated that a flat slab of the metamaterial enables partial focusing of p-polarized electromagnetic radiation. The reported results are supported by full wave simulations and by analytical calculations based on homogenization theory.

The main aim of this work is to carry out an exhaustive analysis of transmission lines loaded with open split ring resonators (OSRRs) and open complementary split ring resonators (OCSRRs). These particles are electrically small open resonators (inspired in the split ring resonator—SRR), which can be series or shunt connected to a host transmission line for the synthesis of microwave components, including designs based on transmission line metamaterials. We will analyze both microstrip and coplanar waveguide (CPW) transmission lines loaded with OSRRs and OCSRRs, and we will show that by combining both open resonators (OSRRs and OCSRRs), it is possible to implement composite right/left handed (CRLH) lines with similar characteristics to those based on the CL-loaded approach.

We use a previously developed approach to study stationary TM-type waves propagating in two-dimensional nonlinear optical metamagnetics, pertinent to a separate class of metamaterials with a significant magnetic response at optical frequencies. Since an implicit equation for the nonlinear dielectric functions should be resolved, the TM-type waves within the standard E-field formulations of nonlinear optics cannot be treated using a purely scalar H-field context. We use the optically controlled isotropic Kerr-type nonlinearity to illustrate the proposed approach, while analyzing the performance of an optically tunable metamagnetic. The simulation results prove the expected tuning of the magnetic resonance within a 100-nm band around the center wavelength of 1.55 μm.