Existence, uniqueness and finite element approximation of solution of time-harmonic electromagnetic boundary value problems involving metamaterials

Existence and uniqueness of the solution of time-harmonic electromagnetic boundary value problems is analyzed together with the convergence of Galerkin finite element approximations. Sufficient conditions based on the presence of different types of losses and on the properties of the hermitian symmetric parts of the effective dielectric permittivity and the effective magnetic permeability are provided. Metamaterials such as double-negative, epsilon-negative and mu-negative substances are covered by our analysis since any hypothesis on the positive definiteness of the aforementioned hermitian symmetric parts is avoided on purpose

Detection of Buried Inhomogeneous Elliptic Cylinders by a Memetic Algorithm

The application of a global optimization procedure to the detection of buried inhomogeneities is studied in the present paper. The object inhomogeneities are schematized as multilayer infinite dielectric cylinders with elliptic cross sections. An efficient recursive analytical procedure is used for the forward scattering computation. A functional is constructed in which the field is expressed in series solution of Mathieu functions. Starting by the input scattered data, the iterative minimization of the functional is performed by a new optimization method called memetic algorithm. (c) 2003 IEEE. Personal use of this material is permitted. Permission from IEEE must be obtained for all other users, including reprinting/ republishing this material for advertising or promotional purposes, creating new collective works for resale or redistribution to servers or lists, or reuse of any copyrighted components of this work in other works

Reconstruction of velocity profiles of two-dimensional targets by an inverse scattering procedure based on a numerical forward solver

In this contribution we investigate the capabilities of inverse scattering procedures for electromagnetic problems involving axially moving cylinders, without any restriction on their number, their shapes and their profiles of relative dielectric permittivity and axial velocity. As usual, the inverse scattering problems of interest are recast as optimization problems. An Ant Colony Optimization procedure is adopted to numerically solve these problems. It exploits a proprietary finite element code for the solution of forward scattering problems involving objects in motion. When the maximum magnitude of the axial speed is limited to one-hundredth of the speed of light in vacuum, it has been shown that it could be convenient to split the inverse problem into two parts (M. Pastorino, M. Raffetto, and A. Randazzo, IEEE Trans. Geosci. Remote Sens., 53, 2015, pp. 1452-1462): the first one related to the reconstruction of the geometrical and dielectric unknowns while the second part has to deal with the determination of the velocity profile. In this work we focus, in particular, on the latter one

Pros and cons of microwave imaging techniques for the reconstruction of velocity profiles of cylindrical targets in axial motion

In this contribution the strengths and the weaknesses of microwave imaging techniques for the reconstruction of dielectric and velocity profiles of inhomogeneous cylinders in non-uniform axial motion are presented. Some numerical results are presented to support the main conclusions

Comparison among Cognitive Radio Architectures for Spectrum Sensing

Recently, the growing success of new wireless applications and services has led to overcrowded licensed bands, inducing the governmental regulatory agencies to consider more flexible strategies to improve the utilization of the radio spectrum. To this end, cognitive radio represents a promising technology since it allows to exploit the unused radio resources. In this context, the spectrum sensing task is one of the most challenging issues faced by a cognitive radio. It consists of an analysis of the radio environment to detect unused resources which can be exploited by cognitive radios. In this paper, three different cognitive radio architectures, namely, stand-alone single antenna, cooperative and multiple antennas, are proposed for spectrum sensing purposes. These architectures implement a relatively fast and reliable signal processing algorithm, based on a feature detection technique and support vector machines, for identifying the transmissions in a given environment. Such architectures are compared in terms of detection and classification performances for two transmission standards, IEEE 802.11a and IEEE 802.16e. A set of numerical simulations have been carried out in a challenging scenario, and the advantages and disadvantages of the proposed architectures are discussed

Unsupervised Synthesis of Microwave Components by Means of an Evolutionary-Based Tool Exploiting Distributed Computing Resources

A parallel implementation of an automatic CAD tool based on the parallel virtual machine software package, genetic algorithms and finite element simulators is presented. It is shown that the parallel implementation can be obtained by developing just a few hundred lines of code and a pseudocode description is provided. Finally, selected numerical results are provided in order to show the effectiveness and the reliability of the proposed approach

Discrete compactness for edge elements in the presence of mixed boundary conditions

It is shown—for the first time, to the best of the author’s knowledge—that when the finite dimensional space sequence is generated by using Nedelec’s edge elements of any order and of both families defined on tetrahedra, the so-called discrete compactness property holds true for Lipschitz polyhedra even in the presence of mixed boundary conditions. The family of meshes is not required to be quasi-uniform but just regular. A standard way to deal with general dielectric permittivities completes the picture

REALISTIC AND CORRECT MODELS OF IMPRESSED SOURCES FOR TIME-HARMONIC ELECTROMAGNETIC BOUNDARY VALUE PROBLEMS INVOLVING METAMATERIALS

The aim of this work is to analyze the role of the impressed sources in determining the well or ill-posedness of time harmonic electromagnetic boundary value problems involving isotropic effective media. It is shown, in particular, that, even if all interfaces are regular, the class of ill-posed problems can be very large in the presence of general square-integrable impressed sources. However, when a simple and realistic constraint is enforced on these sources, requiring that the support of the sources does not include any interface between a traditional medium and a metamaterial, among the problems here considered just those involving an interface between complementary materials remain ill-posed. These considerations have a very significant impact also on the approximability of the solution of well-posed problems since the numerical noise can introduce small fictitious sources even where the sources to be simulated are not present. These effects on finite element simulators are fully analyzed. Finally, we propose an algorithm that allows to obtain much better approximations of the solutions of the most critical well-posed problems. </jats:p

Well posedness and finite element approximability of two-dimensional time-harmonic electromagnetic problems involving non-conducting moving objects with stationary boundaries

A set of sufficient conditions for the well-posedness and the convergence of the finite element approximation of two-dimensional time-harmonic electromagnetic boundary value problems involving non-conducting moving objects with stationary boundaries is provided for the first time to the best of authors' knowledge. The set splits into two parts. The first of these is made up of traditional conditions, which are not restrictive for practical applications and define the usual requirements for the domain, its oundary, its subdomains and their boundaries, the boundary conditions and the constitutive parameters. The second part consists of conditions which are specific for the problems at hand. In particular, these conditions are expressed in terms of the constitutive parameters of the media involved and of the velocity field. It is shown that it is not difficult to check the validity of these conditions and that they hold true for broad classes of practically important problems which involve axially moving media