Propagation through metamaterial temporal slabs: transmission, reflection and special cases

Time-varying metamaterials are artificial materials whose electromagnetic properties change over time. In earlier studies, the equivalent reflection and transmission coefficients at a temporal interface have been derived. Here, we extend the study to a temporal slab, i.e., a uniform homogeneous medium that is present in the space for a limited time. We derive the transmission and reflection coefficients for a metamaterial temporal slab as a function of the refractive indices and application time. Similarly to the role played by the electrical thickness for spatial slabs, we show that the response of the temporal slab can be controlled through the application time. The preliminary results reported here may pave the way to several novel devices based on temporal discontinuities

Dominantni mod gustoće struje na spiralnoj patch anteni

An elegant and efficient way to calculate and analytically show the main features of spiral patch antennas is presented in this paper. The derivation of an approximate analytical expression for the dominant current density mode on the patch is initially presented, from which it can be easily calculated the patch radiation pattern. Its invariance with frequency scaling, which is the main feature of such log-periodic antennas, is in particular shown, together with a good congruency with experimental results. An extension to higher-order modes for a MoM analysis of the current density is then suggested, which may be useful to study with higher accuracy the other antenna characteristics, such as gain and input impedance at the feed.U radu je prikazan privlačan i djelotvoran pristup proračunu i analitičkom prikazu spiralnih patch antena. Prvo je izveden aproksimativni analitički izraz za dominantni mod gustoće struje na spiralnom patchu. Pomoću izvedenog izraza moguće je jednostavno izračunati dijagrame zračenja patch antene. Proračunom je potvrđeno da se dijagrami zračenja ovakve log-periodičke antene ne mijenjaju s frekvencijom. Utvrđeno je dobro podudaranje proračuna dijagrama zračenja s rezultatima mjerenja. Predloženo je proširenje za više modove gustoće struje pogodne za analizu patch antene pomoću metode momenata. Primjenom metode momenata uz predloženo proširenje višim modovima može se s većom točnošću proučavati i druge osobine antene kao npr. dobitak i ulazna impedancija

Scattering cancellation by metamaterial cylindrical multilayers

In this paper, we present the theoretical analysis and the design of cylindrical multilayered electromagnetic cloaks based on the scattering cancellation technique. We propose at first the analysis and the design of bi-layered cylindrical shells, made of homogenous and isotropic metamaterials, in order to effectively reduce the scattered field from a dielectric cylindrical object. The single shell and the bi-layered shell cases are compared in terms of scattering reduction and loss effects. The comparison shows that the bi-layered configuration exhibits superior performances. The scattering cancellation approach, is, then, extended to the case of generic multilayered cylindrical shells, considering again homogeneous and isotropic metamaterials. The employment of the proposed technique to the case of cloaking devices working at multiple frequencies is also envisaged and discussed. Finally, some practical layouts of cylindrical electromagnetic cloaks working at optical frequencies are also proposed. In these configurations, the homogenous and isotropic metamaterials are replaced by their actual counterparts, obtained using alternating stacked plasmonic and non-plasmonic layers. The theoretical formulation and the design approaches presented throughout the paper are validated through proper full-wave numerical simulations

Synthesis of Filtering Structures for Microstrip Active Antennas Using Orlov's Formula

In this paper, a synthesis technique for nonuniform filtering structures to be employed in active integrated antenna layouts is presented. The idea is to suppress the higher harmonic contribution due to the presence of nonlinear components through a nonuniform transmission line properly designed via Orlov's synthesis formula. The theory presented is applied here to synthesize an amplifier-based active antenna layout for wireless local area network (WLAN) purposes working at 2.4 GHz. The numerical results presented show the capabilities of the proposed approach

METAMORPHOSE VI – the Virtual Institute for Artificial Electromagnetic Materials and Metamaterials: Origin, mission, and activities

In this paper, we outline the background, mission, and activities of the Virtual Institute for Artificial Electromagnetic Materials and Metamaterials (METAMORPHOSE VI). This international association, founded in the framework of the FP-6 Network of Excellence METAMORPHOSE, aims at promoting and developing research, training, and dissemination activities in the emerging and highly dynamic field of advanced electromagnetic materials and metamaterials at both European and International levels. More than 300 researchers are currently associated with the METAMORPHOSE VI which networks them together in a learnt society. After a brief description of the association and its mission, we present an overview of the activities developed by the METAMORPHOSE VI, with a particular emphasis on the coordination of the European Doctoral Program on Metamaterials (EUPROMETA) and the organization of the International Congress on Advanced Electromagnetic Materials in Microwaves and Optics – metamaterials congress

Theory and Simulations of a Conformal Omni-Directional Sub-Wavelength Metamaterial Leaky-Wave Antenna

The detailed theory of a single subwavelength conformal radiator that exploits the resonant properties of thin cylindrical metamaterial shells supporting leaky waves is presented. It is shown and reviewed analytically and numerically how a circularly symmetric resonant leaky mode may be supported by a properly designed subwavelength homogenous cylindrical shell of low negative permittivity. Some physical insights are provided and numerical simulations with a feed point, considering also the finiteness of the antenna in the longitudinal direction, are presented and discussed. Moreover, possibilities and limitations of a practical realization of this setup are mentioned, considering in details the possible anisotropies in the metamaterials

Anomolous Properties of Scattering from Cavities Partially Loaded With Double-Negative or Single-Negative Materials

In this paper, the theoretical justification and the numerical verification of the anomalous scattering from cavities partially filled with metamaterials are presented. A hybrid numerical formulation based on the Finite Element Method (FEM) and on the Boundary Integral (BI) for the analysis of cavity backed structures with complex loading metamaterials is first presented. The proposed approach allows the analysis of cavities filled with materials described by tensorial linear constitutive relations, which may well describe artificial metamaterials synthesized with proper inclusions in a host dielectric. It is found that cavities loaded with pairs of metamaterial layers with resonant features possess unusual scattering properties, and with judicious selection of constitutive parameters for these materials the transparency effect or significant enhancement in the backscattering from such cavities are obtained. This may be considered as a first step towards the analysis of the scattering and radiating features of cavity-backed patch antennas and reflect-arrays in presence of multilayered metamaterial loads