Showing papers in "Electromagnetics in 2005"

Negative Refraction in Perspective

Abstract: The concept of negative refraction is attracting a lot of attention. The initial ideas and the misconceptions that have arisen are discussed in sufficient detail to understand the conceptual structure that binds negative refraction to the existence of backward wave and forward wave phenomena. A presentation of the properties of isotropic media supporting backward waves is followed by a discussion of negative phase velocity media, causality, anisotropic crystals, and some connections to photonic crystals. The historical background is always coupled to a detailed presentation of all the issues. The paper is driven numerically and is illustrated with the outcomes of original FDTD simulations.

A Network Formulation of the Power Balance Method for High-Frequency Coupling

Abstract: This paper deals with a network formulation of the power balance approach in order to estimate high frequency coupling mechanisms in complex systems. After giving the general principles of this approach found in the scientific literature, the network development of the method is presented, based on an electromagnetic topology analysis. Finally, the network formulation of this approach is applied on a simple two contiguous cylindrical structure by easily adapting a computer code initially dedicated to electromagnetic topology on cable networks.

Natural and Nanoengineered Chiral Reflectors: Structural Color of Manuka Beetles and Titania Coatings

Abstract: A parallel study of natural and nanoengineered structurally chiral reflecting coatings is described. It is shown that the nanostructures are different in a minor way but are optically equivalent. Refractive index matching of nanoengineered chiral coatings on a plane substrate is shown to improve the saturation of structural color. Optical and electron microscopies reveal complexity in the multilayered chiral coatings that produce green metallic-like reflections from manuka (scarab) beetles. In particular, the reflectors are shown to have the form of small concave pits and troughs that are filled with contouring chiral material. Each chiral microreflector presents a range of pitch and tilt to an incident beam of light. Physical properties of the textured coatings are related to optical properties such as spectral reflectance, angle of spread, and perceived color, which has a high degree of saturation due to the filling of the pits. Observations of overlapping chiral mediums in beetle reflectors have inspir...

Linear and Nonlinear Homogenized Composite Mediums as Metamaterials

Abstract: Metamaterials are artificial composites which are characterized by physical properties that are not possessed, either to the same extent or at all, by their component phases. Homogenization provides a means of conceptualizing such metamaterials. The constitutive parameters of homogenized composite mediums (HCMs) may be estimated through the implementation of well-established homogenization formalisms. In particular, those of Maxwell Garnett and Bruggeman, as well as the more comprehensive strong-property-fluctuation theory, are discussed here in the context of HCM metamaterials. We present a survey of five generic examples of metamaterials; each example is envisaged as an HCM. The unusual structures and properties of these HCM metamaterials are emphasized. First, we examine bianisotropic HCMs as metamaterials. While bianisotropy is rarely observed in naturally occurring materials, bianisotropic HCMs may be readily conceptualized. Second, an anomalous form of plane wave propagation known as Voigt wave prop...

Superlattice Properties of Helical Nanostructures in a Transverse Electric Field

Abstract: A charge carrier confined in a quasi-one-dimensional helical nanostructure in the presence of an electric field normal to the axis of the helix is subjected to a periodic potential proportional to the strength of the field and the helix radius. As a result, the behavior of this carrier is similar to that in a semiconductor superlattice with parameters controlled by the applied field. This behavior includes Bragg scattering of the charge carrier by a periodic potential, which results in an energy gap opening at the edge of the superlattice Brillouin zone. A certain type of carbon nanotube is shown to possess similar superlattice properties. Modification of the band structure is found to be significant for experimentally attainable electric fields, which raises the possibility of applying this effect to novel nanoelectronic devices.

Optimization of the Method of Auxiliary Sources (MAS) for Scattering by an Infinite Cylinder Under Oblique Incidence

Abstract: This paper presents a rigorous accuracy analysis of the method of auxiliary sources (MAS) for the problem of oblique incidence plane wave scattering by a perfectly conducting, infinite circular cylinder. For this particular scattering geometry, it is shown that the MAS matrix is inverted analytically, via eigenvalue analysis, and an exact mathematical expression for the discretization error is derived. Furthermore, the computational error, resulting from numerical matrix inversion, is calculated and compared to the analytical one, showing perfect fit for a wide range of the auxiliary sources' locations. The irregular behavior of the computational error for small values of the auxiliary sources' radii is explained by the corresponding high values of the linear system's condition number. It is also demonstrated that specific source locations, associated with the characteristic eigenvalues of the scattering problem, should be avoided, because then both computational and analytical error increase ver...

Including Apertures and Cavities in the BLT Formalism

Abstract: In the BLT formalism, based on the electromagnetic topology of a complex system, black boxes (junctions) and multiconductor transmission lines (tubes, especially uniform ones) have long been included. This paper discusses some features, including apertures and cavities in the formalism. This involves the definition of appropriate voltages and currents for inclusion in the scattering matrices.

Electrostatic Excitation of a Conducting Toroid: Exact Solution and Thin-Wire Approximation

Abstract: Laplace's equation is solved via separation of variables in toroidal coordinates for the electrostatic potential external to a conducting torus placed in a uniform electric field and excited by an arbitrarily located point charge. The accuracy of the static thin-wire kernel approximation in an integral equation applied to the circular loop is verified using the exact results in the limit as the toroid shrinks to a ring. An equivalent lineal charge density from the exact solution agrees remarkably well with the integral equation solution for the conducting ring. Since the singularity in the Helmholtz Green's function for the electrodynamic problem is the static singularity considered herein, the results confirm the applicability of the thin-wire kernel to the scattering and radiation problems of the circular loop.

On one- and two-dimensional electromagnetic band gap structures in rectangular waveguides at microwave frequencies

Abstract: Electromagnetic band gap (EBG) structures of two different configurations implemented inside R120 rectangular waveguides (frequency range 10–15 GHz) are examined. The first configuration has a periodic, piecewise uniform variation of permittivity in the propagation direction. Two types of such one-dimensional (1D) EBG structures are analyzed, one with the unit cell comprising two dielectric layers, the other with three dielectric layers per unit cell. The second configuration is two-dimensional, with the unit cell along the propagation direction containing two sections, each of which is made of alternating pillars of two dielectric materials. The Bloch theorem is invoked for the ideal EBG structures, which are infinitely long in the propagation direction. The mode-matching method (MMM) is used for real 1D-EBG structures, which contain a finite number of unit cells, whereas a combination of the coupled-mode method (CMM) and the MMM is used for real 2D-EBG structures. Spectrums of the transmission coefficie...

Determining Resonant Frequencies of Various Microstrip Antennas within a Single Neural Model Trained Using Parallel Tabu Search Algorithm

Abstract: Artificial neural networks (ANNs) are one of the popular intelligent techniques in solving engineering problems. In this paper, an intelligent new approach based on ANN trained with a parallel tabu search (PTS) algorithm to determine the resonant frequencies of microstrip antennas of regular geometries is presented. A single ANN model was used to determine the resonant frequencies of the rectangular, circular, and triangular microstrip antennas. The determination performance of a single neural model was improved with the help of PTS. The results obtained from the single neural model for the resonant frequencies of the rectangular, circular, and triangular microstrip antennas are in very good agreement with the experimental and other methods presented in the literature.

The Thickness Dependence of Resonance Frequency in Anisotropic Composites with Long Conductive Fibers

Abstract: The resonant frequency of long conductive fibers embedded in an anisotropic composite as a function of layer thickness is studied both numerically and experimentally and is discussed in terms of the equivalent permittivity of the layer. A simple empirical exponential law is suggested to fit the thickness dependence of the equivalent permittivity. The law involves a critical thickness value, below which the layer can no longer be treated as a bulk material for a fiber of given length and thickness. The critical thickness is retrieved from numerical data for different permittivity values of isotropic and anisotropic layers and for different fiber length.

Coupling onto Wires Enclosed in Cavities with Apertures

Abstract: This paper presents a hybrid numerical method for the electromagnetic field coupling into apertures residing on the surface of rectangular cavities. The cavity may enclose wires and cables that are typically modeled via transmission line approaches. Coupling into the cavity is analyzed via the moment method along with the cavity Green's function to find the aperture fields whereas Pocklington's integral equation is adapted for the wire/cable currents. The combined wire and aperture integral equation system can be solved directly or by decomposing it into the aperture and wire subsystems. The latter decomposition leads to a two-step or a multistep iterative approach for the solution of the aperture and wire currents. Of importance in this analysis is the use of acceleration algorithm for improving the convergence of the modal Green's function series after the application of the moment method. Issues associated with the large condition of the matrix systems near cavity resonances are also addressed.

An Efficient Hybrid Method for Calculating the EMC Coupling to a Device on a Printed Circuit Board inside a Cavity by a Wire Penetrating an Aperture

Abstract: An efficient hybrid method is developed for calculating the coupling to a device on a printed circuit board inside a cavity. The printed circuit board is connected to a wire or cable that penetrates an aperture in the cavity enclosure. The method uses a combination of transmission-line analysis and a full-wave solver, and a decomposition of the problem into interior and exterior problems for maximum efficiency. Results are presented to verify the accuracy of the proposed method and to study the effects of cavity resonances on the coupling to a device inside the cavity.

Calculable Dipole Antenna for EMC Measurements with Low-Loss Wide-Band Balun from 30 MHz to 2 GHz

Abstract: A half-wavelength calculable dipole antenna has been developed. The Antenna Factor (AF) of this dipole is evaluated between 30 MHz and 2 GHz. Generally the proposed formula by ANSI-63.5 (ANSI, 1988) method for EMI antenna calibration is for a resonant dipole and assumes a perfect sinusoidal current density along the dipole. Indeed, the mutual effects on AF in this case could be taken into account with some approximate correction factors. The perfect sinusoidal form of current density is not correct for the real thick dipoles. For these dipoles, i.e., nonresonant and thick, assuming a perfect sinusoidal current density introduces errors around 1 dB/m on AF. An alternative method is presented: an analytical method based on a simple new current distribution along the dipoles to evaluate their radiation characteristics, and this is compared with a numerical approach based on MoM (the Method of Moments) by NEC software, to model two dipoles in a standard site. The entire frequency range, 30 MHz to 2 GHz, is co...

Performance of Compact Integratable Broadband Microstrip Antenna

Abstract: Performance of a novel integratable broadband antenna employing inverted microstrip circular patch (IMCP) is presented based on the simulation and experimental studies. The antenna geometry embodies dual stacked patches printed back to back on a single substrate in an inverted microstrip configuration. Unlike previous designs, the present stacked patch offers easy integration of active devices with large bandwidth without any enhancement in weight, volume or cost. The design is built up in steps through optimizing the antenna parameters using an HFSS full wave solver and the steps are verified experimentally, showing close agreement between them. Nearly 15% SWR < 2 bandwidth has been reported. Over 90% radiation efficiency with 7 dBi gain is evident from the simulation data. Principal plane radiation patterns are examined using numerical and experimental data, revealing its suitability for mobile communication equipment.

Equivalent circuit for antenna-cavity coupling in wheeler's cap technique

Abstract: An equivalent circuit is derived for an antenna coupled to a shielding cavity via field analysis. The input impedance of the antenna inside the cavity is then studied theoretically and experimentally. It is shown that the input resistance of the antenna shielded by the cavity is not merely the loss resistance, but is actually the sum of the antenna loss resistance and the coupling resistance between the antenna and cavity. This coupling effect is demonstrated quantitatively by numerical computations for dipole antennas. A method is proposed to avoid the antenna-cavity antiresonance in the measurement of loss resistance of the antenna.

Electromagnetic Topology-Based Analysis of Coupling through Small Aperture on Cables of Communication Systems

Abstract: The interactions and coupling between an external source and the cables of a digital communication system through a small aperture have been analyzed through the electromagnetic topology technique for simulations. Using an alternate approach to transfer function generation in the state-of-the-art topological code and by utilizing experimentally determined S-parameters of a cable network linked to personal computers, the response of the cables to lightning and electromagnetic pulses has been studied. The simulation results show that external fields on the cable current depend strongly on cable lengths, locations, and terminating impedances. Analysis also shows that damage to cables or soft errors on data transmission is more pronounced at high-frequency electromagnetic pulses, compared to lightning.

An Efficient Procedure for the Projection of a Given Field onto Hierarchical Vector Basis Functions of Arbitrary Order

Abstract: In contrast to interpolatory basis functions, the projection of a given field onto hierarchical vector basis functions is rather difficult and could be costly if not done with some effort at efficiency. The lack of any interpolatory points for the hierarchal basis functions is the underlying reason for the necessity of a more involved method compared to that for interpolatory basis functions. We present a method to project an arbitrary given field onto hierarchical vector basis functions that is an extension of a projection method proposed in an earlier paper by Webb. The main improvements of the new procedure are its ability to project a given field residing in a volume onto the vector basis functions of an arbitrary order as well as its ability to handle an arbitrary geometrical element mapping scheme that enables the use of tetrahedrons with curvilinear faces. The procedure is efficient in that it projects the field by solving a series of small and easily manageable systems of equations. Moreover, the ...

Selective Reflection and Transmission from Perturbed Chiral Sculptured Thin Films

Abstract: The effects of varying the angle of rise as a function of depth are investigated for chiral sculptured thin films. A matrix differential equation describing the propagation of light in the film which may result from plane waves at normal as well as oblique angles of incidence is developed. Using the piecewise homogeneity approximation, reflectance and transmittance spectrums are then determined for chiral thin films of TaO2 with periodic perturbations in the angle of rise as a function of depth into the film. Available empirical data are used to realistically model the dielectric and structural characteristics of the perturbed films. The effects on Bragg reflections of various orders are described for each perturbation.

Mitigation of Power Frequency Fields by Proper Choice of Line Configuration and Shielding

Abstract: Although the hazards of power line magnetic fields on human health are not firmly established, mitigation of these fields is prudent. In this paper, some of the possible hazards of these magnetic fields are discussed first, and then an attempt is made to reduce these fields by proper choice of parameters of conventional three-phase power lines and by shielding confined regions such as switching stations or control rooms. Numerical procedures are developed, computations are made, and results are presented to show that techniques such as proper choice of line parameters, active cancellation, and local shielding reduce such magnetic fields to acceptable levels.

Convergent Galerkin MoM Solution for 2-D H-Scattering from Screens

Abstract: A two-dimensional Neumann problem solution is obtained in the first-kind hypersingular integral equation (HSIE) formulation with the aid of the Galerkin method of moments (GMoM) on the complete orthogonal basis. Convergence and uniqueness of the GMoM solution to the HSIE is proved in the Hilbert space of square integrable functions (L 2 ) for screens with smooth boundary. The exact relationship between actual and residual errors is also obtained, which permits one to calculate an actual error by integrating residual error along the boundary of a scatterer. The condition number increasing problem is solved by making use of proper preconditioning.

Convergent Galerkin MoM Solver for the EFIE in Two Dimensions

Abstract: The convergence of the entire domain Galerkin MoM solution to the electric field integral equation (EFIE) is provided in the Hilbert space of square integrable functions (L 2 ) for the nonresonant case. To this end, the traditional MoM equation is transformed into a Fredholm second-kind equation in the space of sequences for a smooth closed boundary of a scatterer. A rigorous relation between actual and residual errors is also obtained that permits one to compute the both errors in L 2 . Advantages of the new MoM equation are demonstrated in terms of accuracy and efficiency compared to the traditional MoM equation.

Effects of Multilayers Superstrates on Microstrip Leaky-Wave Antennas Radiating Characteristics and Performances

Abstract: In this paper, a full-wave accurate and versatile solution for multilayers superstrates on microstrip leaky-wave antenna analysis is described. Therefore, setting E and J continuity conditions on radiating aperture provides, a systematic formulation of the integral equation by a periodic discontinuity network where the concept of trial functions is introduced. Since current density is established by analytical expressions, the relevant equation is solved numerically by Galerkin method. The propagation constant of the leaky-wave is obtained by a least squares method. Hence, electronic beam scanning applications and performances are investigated upon layers thickness and dielectric values. Several examples are given and discussed.

Applications of shielding techniques to enhance the antenna performance of mobile communications and reduce SAR induction in the human head

Abstract: Applications of shielding techniques are proposed to enhance the antenna performance of mobile communications. The shielding structures for the base station antennas are based on an implementation of resistive plates that tend to reflect the antenna radiation in the side lobes to main beam region, and hence optimize the overlapping coverage between sectors. On the other hand, magnetic materials are employed to design the shielding structures for handset antennas in order to provide good shielding effectiveness for magnetic near fields that were shown to be the major cause of a specific absorption rate (SAR) in the human head. Our studies show that with this shielding application the antenna performance can be enhanced while simultaneously reducing the SAR induction.

Scattering of Plane Waves at the Junction of Two Corrugated Half-Planes

Abstract: In this paper, the boundary conditions given by Weinstein (1969) are employed to simulate two corrugated half-planes with the same slot height but different slot width. The scattering mechanism at ...

Microwave Imaging of Immersed Dielectric Bodies: An Experimental Survey

Abstract: Diffraction tomography provides a good method for reconstructing cross-section images of weakly scattering dielectric objects. The Born and Rytov approximations are well-known approximations for the first-order diffraction tomography method. In this paper, the restrictions of the Born and Rytov approximations are experimentally investigated when the object is immersed in a medium. Microwave tomography images of several kinds of dielectrics of different shapes and dielectric constants are imaged both in the air and in the sand. It is shown experimentally from the resultant images that the Born approximation produces a better estimation for objects small in size and even for objects of large deviations in relative refractive index; on the other hand, Rytov approximation gives a more accurate estimation mainly for objects with small deviations in relative refractive index. The Rytov approximation is also valid for large-sized objects if the first condition is satisfied. The results also show that it...

Image Reconstruction for a Perfectly Conducting Cylinder Buried in Slab Medium by TE Wave Illumination

Abstract: The electromagnetic imaging of a perfectly conducting cylinder illuminated by transverse electric (TE) wave is investigated. A perfectly conducting cylinder of unknown shape buried in the second layer scatters the incident wave from the first layer or the third layer. The metallic cylinder with cross section described by the equation is illuminated by an incident plane wave whose magnetic field vector is perpendicular to the z axis (i.e., TE polarization). Based on the boundary condition and the recorded scattered field, a set of nonlinear integral equations is derived and the imaging problem is reformulated into an optimization problem. The genetic algorithm is then employed to find out the global extreme solution of the cost function. Numerical results demonstrated that, even when the initial guess is far away from the exact one, good reconstruction can be obtained.

Analysis and Reduction of Electromagnetic Field Leakage through Loaded Apertures: A Numerical Study

Abstract: This paper presents the novel use of resistive sheets to reduce electromagnetic penetration through apertures. The resistive material is applied in several configurations that will be discussed in this paper. Significant reduction of electromagnetic leakage is possible by using loading techniques inspired by a transmission line interpretation of the field distribution within the aperture at or beyond its fundamental resonant frequency. By using the configurations proposed in this work, it is possible to achieve appreciable reduction in the near and far field aperture radiation without affecting the total area needed for airflow and heat transfer. Numerical results are presented using a commercial finite-difference time-domain (FDTD) algorithm to demonstrate the effectiveness of our new approach.

Implanted Spherical Head Model for Numerical EMC Investigation

Abstract: Caution should be exercised when using modern wireless telecommunication devices around sensitive electromedical equipment used in hospital intensive care units. Mobile telephones can also cause interference in certain other medical devices, such as cardiac pace makers and hearing aids. Key issues to address are the questions of whether mobile phones have a detrimental effect on implants, and how the interaction of the handset with the body can be minimized in order to both alleviate public fears and improve handset antenna performance and new prosthetic designs. This work aims to investigate the scattering of an electromagnetic (EM) wave from a perfectly conducting cylindrical implant of electrically small radius (of resonant length), embedded eccentrically into a dielectric spherical head model. The method of dyadic Green's function (DGF) for spherical vector wave functions is used. Analytical expressions for the scattered fields of a cylindrical implant embedded head model is obtained. Numerical result...

Finite-Element Analysis of Scattering From a Complex BOR Using Spherical Infinite Elements

Abstract: Recently, a new type of infinite elements (IFEs) was proposed as an accurate and efficient mesh truncation method for the finite element analysis of open–region acoustic scattering. These IFEs are based on the radial expansion of the scattered field and are used to model the scattered field outside a separable surface characterized by a constant radial coordinate (such as a spherical or a spheroidal surface in three dimensions). In this paper, spherical infinite elements are formulated and implemented for the finite element (FE) analysis of time–harmonic electromagnetic scattering from a complex body of revolution (BOR), and their performance is studied by comparison with the finite element solution using conventional absorbing boundary conditions (ABCs). Numerical results are presented to demonstrate that the new type of infinite elements is indeed more accurate than both the first– and second–order ABCs.