Shielding and Radiation Characteristics of Cylindrical Layered Bianisotropic Structures

In this paper we propose an analytical study in the spectral domain of cylindrical layered structures filled with general bianisotropic media and fed by a 3D electric source. The integrated structure is characterized in terms of transmission matrices leading to an equivalent circuit representation of the whole multilayered structure. Within the framework of this two-port formalism, we present a new contribution to the computation of the Green's function arising in the analysis of multilayered conformal integrated antennas loaded with general bianisotropic materials. We also propose an analytical study of the shielding effectiveness of general bianisotropic materials located in multilayered, cylindrical configuration. The expression of the shielded fields sustained both by plane wave and arbitrary sources is obtained in a closed analytical form. Numerical results are also presented showing effects of electromagnetic parameters on radiation pattern, matching properties and radar cross section of the integrated structure

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

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

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

response to comment on the paper electromagnetic modeling of ellipsoidal nanoparticles for sensing applications

The authors respond to the comments by Mackay and Lakhtakia. First of all, we would like to thank Mackay and Lakhtakia1 who have carefully read our paper and for their valuable comments on our manuscript. We agree that the polarizability is a dyadic. For our aims (analytical models, full-wave simulations, and sensitivity analysis), we have assumed the impinging electromagnetic field as a plane wave having the electric field E parallel to the nanoparticle principal axis (x -axis as depicted in the Fig. 1 of the paper). In this case, Eq. (1) and the following equations refer only to scalar component x ^ x ^ of the dyadic polarizability α − − − − (sufficient to evaluate the nanoparticle response under the aforementioned excitation condition). We have to point out that for sensing applications the analyzed polarization is crucial in order to obtain the best sensitivity performances

Electromagnetic Modeling of Dielectric Mixtures

Electromagnetic modeling of dielectric materials allows us to study the effects of electromagnetic wave propagation and how such electromagnetic fields influence and interact with them.Dielectric materials are composites or mixtures, which often are made up of at least two constituents or phases. Modelling the electromagnetic behaviour of dielectric mixtures is crucial to understand how geometrical factors (shape and concentration), electromagnetic properties of inclusions and background medium, influence the permittivity of the overall material.The aim of this work is to develop new analytical models for dielectric mixtures, in order to describe their electromagnetic behaviour and design them with desired electromagnetic properties, for specific required applications. In particular, in this paper a new general expression for the effective permittivity of dielectric mixture is presented. The mixtures consist of inclusions, with arbitrary shapes, embedded in a surrounding dielectric environment. We consider the hosting environment and the hosted material as real dielectrics, both of them as dispersive dielectrics.The proposed analytical models simplify practical design tasks for dielectric mixtures and allow us to understand their physical phenomena and electromagnetic behaviours

Metamaterial monolayers and bilayers for enhanced transmission through a sub-wavelength aperture in a flat perfectly conducting screen

In this paper, we will provide an overview of our theoretical work on the role of metamaterial covers in dramatically enhancing the wave transmission through a subwavelength aperture over a perfectly conducting flat screen. It is well known that a low-permitivity or a low-permeability grounded slab may support surface polaritons. In our problem these natural modes are exploited to collect and redirect the impinging radiation into the tiny hole and to reshape the radiation pattern at the exit side of the screen towards an observer. The sum of these two effects may potentially lead to a dramatic increase in the total power transmission through the aperture. Moreover, we show how this effect may be further increased and optimized by employing bilayer covers with conjugate materials, i.e., materials with oppositely signed constitutive parameters. In some earlier works, we have indeed utilized such a coupling to induce a compact interface resonance, suggesting several microwave and optical applications. Here, the same resonant phenomenon can lead to the transmission enhancement together with a reduction of the required cover thickness. We provide some insights into the physical basis of this effect, and we speculate some potential applications

Metamaterial Covers Over a Small Aperture

Recently, there has been an increased interest in the problem of wave transmission through sub-wavelength apertures, following successful experimental demonstration by several groups for enhancing optical power transmission through nano-scale holes in metallic screens due to properly designed periodic corrugation. Oliner, Jackson, and their co-workers explained and justified this phenomenon as the result of the excitation of the leaky waves supported by the corrugated screen. Here we discuss in detail the mechanism and analysis for another setup we have recently proposed, in which metamaterial layers with special parameters may be utilized as covers over a single sub-wavelength aperture in a perfectly electric conducting (PEC) flat screen in order to increase the wave transmission through this aperture, and we provide a detailed physical insights and analytical explanation for this aperture setup that may lead to similar, potentially even more pronounced effects when the proper metamaterial layers are used in the entrance and the exit face of the hole in the flat PEC screen with no corrugation. Some numerical results confirming this theory are presented and discussed. We also investigate the sensitivity of the transmission enhancement to the geometrical and electromagnetic parameters of this structure