Zsolt Szabó

A High Gain Antenna With an Optimized Metamaterial Inspired Superstrate

A metamaterial unit cell with a low refractive index over a wide frequency band is proposed and designed. The effective material parameters of the unit cell are extracted, and the unit cell forms a planar three-layer metamaterial structure used as a superstrate for broadside gain enhancement of a patch antenna at 10 GHz. The proposed superstrate is optimized along with the antenna to enhance its beam-focusing ability, taking into account the oblique wave incidence from the radiation source. Both simulation and measurement of the antenna with the optimized superstrate show that this configuration is able to achieve a broadside gain 70%-80% of the maximum gain from the ideal effective radiation surface.

Computer-aided simulation of Stoner–Wohlfarth model

Abstract The simulation of magnetic phenomena in anisotropic materials has several difficulties. The Stoner–Wohlfarth model can describe the magnetisation process in anisotropic materials. In this paper the magnetisation behaviour of the Stoner–Wohlfarth particle will be studied in linear excitation and in rotational magnetic field. The variation of the magnetisation vector can have jumps, these jumps correspond to the Barkhausen effect. The vector hysteresis model will be developed.

Nonlinear analysis of a cantilever pipe containing pulsatile flow

In this paper we investigate the nonlinear dynamics of a cantilever elastic pipe that contains pulsatile flow. The equation of motion was derived by using Hamiltonian action function. We use Galerkins technique to include only finite number of spatial modes in the solution.The stability chart of the time-varying system was computed in the space of the relative perturbation amplitude of the flow velocity and dimensionless forcing frequency using an efficient numerical method based on Chebyshev polynomials. In the near of some critical regions bifurcation diagrams were also computed which show secondary Hopf bifurcations and phase locking followed by chaotic motion.

Application-layer traffic optimization in software-defined mobile networks: A proof-of-concept implementation

Integration of application layer traffic optimization (ALTO) in software-defined mobile networks could have several benefits for orchestration of endpoint selection for distributed services. ALTO can provide guidance, e.g., in the redirection of end users to appropriate in-network cache, content distribution network server or virtual network function instance during service chaining. ALTO service provides appropriate level of abstraction of network and cost maps, enforcing the policies of mobile network operator and optionally other actors, but keeping the privacy of network topology information. SDN controllers can enforce flow redirection and can dynamically provide abstracted network and cost maps to ALTO server. In this paper we present the operation of ALTO in software-defined networks from the point of view of mobile network operators, and describe our proof-of-concept implementation.

Equivalence of Magnetic Metamaterials and Composites in the View of Effective Medium Theories

The electromagnetic response of metamaterials is governed by the collective behavior of engineered electric and magnetic dipoles. Therefore metamaterials may be replaced by hypothetical composites of spherical particles embedded in a host material. The effective electric permittivity and magnetic permeability of such systems can be computed with high-frequency extension of the Maxwell-Garnett mixing rule. The validity of this assumption is discussed and the features of the model are presented by calculating the effective electromagnetic material parameters of a deep subwavelength spherical composite in three different ways: with the Maxwell-Garnett mixing rule, high-frequency mixing rule and directly extracted from transmission reflection data. Afterwards the developed theory is applied to find the parameters of a composite with similar magnetic response as a metamaterial built of split ring resonators or fishnet structures.

Band gaps in photonic crystals with dispersion

Purpose – The paper presents the band gap computation in one‐ and two‐dimensional photonic crystals built up from porous silicon. The frequency dispersion of the dielectric materials is taken into account.Design/methodology/approach – The behavior of the light in a photonic crystal can be well described by the Maxwell equations. The finite difference time domain (FDTD) method is applied to determine the band structure. The frequency dependence of the dielectric constant is taken into account by a sum of second‐order Lorenz poles. The material parameters are determined applying a conjugate gradient‐based minimization procedure. Passing a light pulse of Gaussian distribution through the photonic crystal and analyzing the transmitted wave can explore the photonic bands.Findings – The realized simulations and visualizations can lead to a much better understanding of the behavior of electromagnetic waves in dispersive photonic crystals, and can make possible to set up experimental conditions properly. The obta...

Aberration-free flat lens design for a wide range of incident angles

Aberration-free flat lenses can be created by introducing phase discontinuities with hyperboloidal distribution on a metasurface. These lenses are able to focus light without aberration under axial illumination but suffer from serious aberration in cases of oblique incidence. Here we introduce a simple design, including an aperture stop and a flat lens with a modified phase distribution that has negligible aberration for incident angles in the range of −40° to 40°. With this design, diffraction-limited imaging systems can be created for a wide incident angle range without the need for complex lens systems.

Subwavelength imaging with composite metamaterials

After reviewing the requirements, which have to be satisfied by a metamaterial-based subwavelength imaging system, a thin film lens is reported herein. The material of the lens is a composite of spherical Ag nanoparticles embedded in SiO2 host material. The image of the lens is calculated by solving Maxwell equations with the transfer matrix method. The procedure applies the Maxwell–Garnett mixing rule and high-frequency effective medium theory to calculate the electromagnetic parameters of the composite material. The formula of the composite material, the optimum working frequency, and the thicknesses of the layers are determined by minimizing the absolute difference of the field distribution in the source and image planes. The details of the design procedure are presented, and optimized configurations obtained under different constraints are discussed. The main advantage of the composite lens is that it can eliminate the hot spots present in the images of metallic superlens.

Near-Infrared Invisibility Cloak Engineered With Two-Phase Metal-Dielectric Composites

An electromagnetic cloaking device made with composite materials and operating in the range of near-infrared light is presented. The invisibility cloak is designed with transformation optics and consists of 15 concentric rings of different anisotropic two-phase metal-dielectric composites. The anisotropic material parameters of the nanocomposites are expressed with the Maxwell-Garnett mixing rule. The finite element simulation of the concealment produced by the multilayer nanocomposite is discussed. The geometry of the inclusions and the material parameters of the composites are determined with differential evolution-based optimization.

Demagnetizing field in ferromagnetic sheet

In this paper, an integral equation method is presented for the computation of the magnetization and magnetic field intensity in ferromagnetic materials taking into account the hysteresis phenomena. The magnetic behavior of the ferromagnetic body is described by three-dimensional isotropic vector Preisach model. For the solution of the obtained nonlinear equations the fixed-point technique is used.