Showing papers on "Electromagnetics published in 2000"

The finite element method in electromagnetics

Abstract: This Key Note presents a summary of the development of the Finite Element Method in the field of Electromagnet ic Engineering, together with a description of several contributions of the authors to the Finite Element Method and its application to the solution of electromagnetic problems. First, a self-adaptive mesh scheme is presented in the context of the quasi-static and full-wave analysis of general anisotropic multiconductor arbitrary shaped waveguiding structures. A comparison between two a posteriori error estimates is done. The first one is based on the complete residual of the differential equations defining the problem. The second one is based on a recovery or smoothing technique of the electromagnetic field. Next, an implementation of the first family of Nedelec's curl-conforming elements done by the authors is outlined. Its features are highlighted and compared with other curl-conforming elements. A presentation of an iterative procedure using a numerically exact radiation condition for the analysis of open (scattering and radiation) problems follows. Other contributions of the authors, like the use of wavelet like basis functions and an implementation of a Time Domain Finite Element Method in the context of two-dimensional scattering problems are only mentioned due to the lack of space.

Electromagnetic contributions to single-molecule sensitivity in surface-enhanced Raman scattering

Abstract: We examine whether single molecule sensitivity in surface-enhanced Raman scattering (SERS) can be explained in the framework of classical electromagnetic theory. The influence of colloid particle shape and size, composition (Ag or Au) and interparticle separation distance on the wavelength-dependent SERS enhancement factor is reported. Our calculations indicate that the maximum enhancement factor achievable through electromagnetics is of the order 10(11). This is obtained only under special circumstances, namely at interstitial sites between particles and at locations outside sharp surface protrusions. The comparative rarity of such sites, together with the extreme spatial localization of the enhancement they provide, can qualitatively explain why only very few surface sites seem to contribute to the measured signal in single-molecule SERS experiments. Enhancement factors of the order 10(14)-10(15), which have been reported in recent experiments, are likely to involve additional enhancement mechanisms such as chemisorption induced resonance Raman effects.

Numerical Techniques in Electromagnetics, Second Edition

Abstract: Numerical Techniques in Electromagnetics is designed to show the reader how to pose, numerically analyze, and solve electromagnetic (EM) problems. It gives them the ability to expand their problem-solving skills using a variety of available numerical methods. Topics covered include fundamental concepts in EM; numerical methods; finite difference methods; variational methods, including moment methods and finite element methods; transmission-line matrix or modeling (TLM); and Monte Carlo methods. The simplicity of presentation of topics throughout the book makes this an ideal text for teaching or self-study by senior undergraduates, graduate students, and practicing engineers.

On optimization techniques for solving nonlinear inverse problems

Abstract: This paper considers optimization techniques for the solution of nonlinear inverse problems where the forward problems, like those encountered in electromagnetics, are modelled by differential equations. Such problems are often solved by utilizing a Gauss-Newton method in which the forward model constraints are implicitly incorporated. Variants of Newton's method which use second-derivative information are rarely employed because their perceived disadvantage in computational cost per step offsets their potential benefits of faster convergence. In this paper we show that, by formulating the inversion as a constrained or unconstrained optimization problem, and by employing sparse matrix techniques, we can carry out variants of sequential quadratic programming and the full Newton iteration with only a modest additional cost. By working with the differential equation explicitly we are able to relate the constrained and the unconstrained formulations and discuss the advantages of each. To make the comparisons meaningful we adopt the same global optimization strategy for all inversions. As an illustration, we focus upon a 1D electromagnetic (EM) example simulating a magnetotelluric survey. This problem is sufficiently rich that it illuminates most of the computational complexities that are prevalent in multi-source inverse problems and we therefore describe its solution process in detail. The numerical results illustrate that variants of Newton's method which utilize second-derivative information can produce a solution in fewer iterations and, in some cases where the data contain significant noise, requiring fewer floating point operations than Gauss-Newton techniques. Although further research is required, we believe that the variants proposed here will have a significant impact on developing practical solutions to large-scale 3D EM inverse problems.

Fresnal Zones in Wireless Links, Zone Plate Lenses and Antennas

Abstract: From the Publisher: The first book devoted solely to Fresnel zones in microwave/mm-wave electromagnetics, this comprehensive survey covers theory, design and practical applications. Whether you are an experienced electromagnetics specialist or a newcomer to the field, whether you need practical design guidelines or a clear and concise exposition of the fundamentals, you'll find this book invaluable. Written by an acknowledged expert, the volume includes a detailed description of the application of Fresnel zones to microwave wireless communication links as well as a comprehensive description of the state-of-the-art in newly created zone plate lens and antenna technologies. It also contains an overview of the basic electromagnetic equations for time harmonic fields, and a thorough treatment of the Fresnel-Kirchoff diffraction theory. If you are a researcher, practising engineer or student in wireless/electromagnetics, this authoritative resource will help you to understand Fresnel zones, zone plate devices and their practical uses, in particular the analysis and design of microwave communication links, Fresnel zone antennas for DBS, Fresnel zone plate lenses for radio telescopes, and conformal curvilinear zone plate antennas. The work is generously illustrated.

Modeling electromagnetic propagation in the Earth-ionosphere waveguide

Abstract: The ionosphere plays a role in radio propagation that varies strongly with frequency. At extremely low frequency (ELF: 3-3000 Hz) and very low frequency (VLF: 3-30 kHz), the ground and the ionosphere are good electrical conductors and form a spherical Earth-ionosphere waveguide. Many giants of the electromagnetics (EMs) community studied ELF-VLF propagation in the Earth-ionosphere waveguide, a topic which was critically important for long-range communication and navigation systems. James R. Wait was undoubtedly the most prolific publisher in this field, starting in the 1950s and continuing well into the 1990s. Although it is an old problem, there are new scientific and practical applications that rely on accurate modeling of ELF-VLF propagation, including ionospheric remote sensing, lightning remote sensing, global climate monitoring, and even earthquake precursor detection. The theory of ELF-VLP propagation in the Earth-ionosphere waveguide is mature, but there remain many ways of actually performing propagation calculations. Most techniques are based on waveguide mode theory with either numerical or approximate analytical formulations, but direct finite-difference time-domain (FDTD) modeling is now also feasible. Furthermore, in either mode theory or FDTD, the ionospheric upper boundary can be treated with varying degrees of approximation. While these approximations are understood in a qualitative sense, it is difficult to assess in advance their applicability to a given propagation problem. With a series of mode theory and FDTD simulations of propagation from lightning radiation in the Earth-ionosphere waveguide, we investigate the accuracy of these approximations. We also show that fields from post-discharge ionospheric currents and from evanescent modes become important at lower ELF (/spl lsim/500 Hz) over short distances (/spl lsim/500 km). These fields are not easily modeled with mode theory, but are inherent in the FDTD formulation of the problem. In this way, the FDTD solution bridges the gap between analytical solutions for fields close to and far from the source.

Engineering Electromagnetics

Abstract: The applications involving electromagnetism are so pervasive that it is difficult to estimate their contribution to modern life: generation and transmission of electric energy, electric motors and actuators, radio, television, magnetic information storage, and even the mundane little magnet used to hold papers to the refrigerator all use electromagnetic fields. This text not only provides students with a good theoretical understanding of electromagnetic field equations but it also treats a large number of application. No topic is presented unless it is directly applicable to engineering design or unless it is needed for the understanding of another topic. Included in this new edition are more than 400 examples and exercises, exercising every topic in the book, 600 end-of-chapter problems, many of them applications or simplified applications. A new chapter introducing numerical methods into the electromagnetic curriculum discusses the finite element, finite difference and moment methods. The book is a comprehensive two-semester textbook. It is written in simple terms with all details of derivations included and all steps in solutions listed. It requires little beyond basic calculus and can be used for self study. The wealth of examples and alternative explanations makes it very approachable by students.

Optimum population size and mutation rate for a simple real genetic algorithm that optimizes array factors

Abstract: There has been an explosion of papers describing applications of a genetic algorithm (GA) to electromagnetics problems. Most of the work has followed traditional GA philosophy when choosing the population size and mutation rate of the genetic algorithm. This paper reports the results of experiments to determine the optimum population size and mutation rate for a simple real genetic algorithm. The choice of population size and mutation rate can cause the run time of the GA to vary by several orders of magnitude. The results of this investigation show that a small population size and relatively large mutation rate is far superior to the large population sizes and low mutation rates that is used by most of the papers presented in the electromagnetics community and by the GA community at large. The results of the numerical experiments presented in this paper suggest that the best mutation rate for GAs lies between 5 and 20% while the population size should be less than 16.

The Assessment of Marine Gas Hydrates Through Electrical Remote Sounding: Hydrate Without a BSR?

Abstract: Marine gas hydrates, prevalent in offshore sediments in Canada and Japan, are a possible hydrocarbon resource, a hazard to drilling and a source of a major greenhouse gas. Quantitative estimates of hydrate concentrations in deep sea sediment are difficult to obtain by conventional methods. We have sought novel techniques specifically designed for assessment such as transient electric dipole-dipole electromagnetics. The latter method is based on the assumption of a reduced electrical conductivity in hydrate rich zones. Field trails of new apparatus on the Cascadia margin have proven successful. Excellent data were collected and analysed using a differential phase method to reduce systematic error. Apparent resistivities collected on three lines demonstrate that the resistivity of the seafloor is remarkably uniform over the whole survey area. The average hydrate concentration, deduced with the aid of a reference model based on the electrical logs of ODP holes 888 and 889, is about 17–26% of pore space (9–13% of sediment volume) in the 100 m interval above the BSR. The values are consistent with those obtained by other analyses. Further, the presence of hydrate is predicted in a region to the east of 889B where there is no visible BSR.

Design, fabrication, and testing of a bistable electromagnetically actuated microvalve

Abstract: A bistable electromagnetically actuated microvalve was designed, processed, and tested. The valve was designed to control a water flow of 0.05-0.5 /spl mu/s from a reservoir at a pressure of 1-2000 Pa. The two valve components were fabricated in silicon, the upper piece comprises an electroplated gold coil, and the lower piece is an Ni/Fe alloy beam. The bistable capability was achieved by balancing the elastic forces on the beam with the magnetic forces due to a 46-/spl mu/m-thick rolled magnetic foil. The design includes the flow through the orifice, squeeze film damping due to beam motion, beam elasticity, and electromagnetics. The microvalve was tested for power consumption, flow rate, time response, Ni/Fe alloy composition, and magnetic foil properties. The valve operates at 1-2 V in both air and water.

Finite element methods in electrical power engineering

Abstract: This book is designed to give the theoretical foundation needed by the new user of finite elements in electrical power engineering, and shows how the equipment designer can benefit from finite element analysis. It is divided into three parts; theory, modelling,and application of the finite element method. The first part outlines relevant electromagnetics, including treatment of boundaries, saturation and permanent magnets. It also shows how the finite element equations can be formulated. The presentation throughout is aimed at giving the reader a physical understanding of the process. The second part deals with special aspects of finite element modelling of engineering problems, including problem formulation, data generation and post processing and emphasises the importance of engineering judgement. The final part is an assembly of 'real' magnetic and electric field problems solved by finite elements, including application to turbine generators, permanent magnet machines, switched reluctance drives, induction motors, transformers and bushings.

The field equivalence principle: illustration of the establishment of the non-intuitive null fields

Abstract: The field equivalence principle, one of the fundamental concepts in electromagnetics, has numerous applications. However, for a beginning student, it is not easy to understand this concept thoroughly and to appreciate it. The dilemma faced by beginning students is illustrated. We have sources in a finite Region I, and an arbitrary mathematical surface separating Regions I and II. The equivalent problems for the exterior and interior regions are specified with the use of electric and magnetic equivalent currents impressed on the boundary surface. The acceptance of the establishment by the equivalent sources of the non-intuitive null field for the exterior problem (by the equivalent sources and the original source for the interior problem) is commonly bothersome and not comfortably realized. In order to clarify this, we revisit Love's and Schelkunoff s forms of the equivalence principle. Subsequently, we discuss two simple, analytically tractable illustrative examples, consisting of plane-wave fields in two half-space regions, separated by an infinite planar surface. In particular, the emphasis is on the establishment of the non-intuitive null fields developed by these equivalent sources. Various forms of equivalence are illustrated by simple analytical field expressions.

Electromagnetics of substorm onsets in the near‐geosynchronous plasma sheet

Abstract: A search of the CRRES database identified 20 events in which the satellite was located within the local-time sector spanned by the substorm current wedge (SCW) as it formed. Poynting vectors for low-frequency waves are derived from the electric and magnetic field measurements. In 19 of the events, data are inconsistent with the notion that the SCW initiates from the braking of earthward bulk flows emanating from a near-Earth X line. Rather, the data support drift-Alfven ballooning in the near-geosynchronous plasma sheet as being responsible for initiation of the SCW and substorm onset. Dipolarization at CRRES is preceded by eastward excursions of the electric field (trigger waves), at which time the first significant electromagnetic energy is observed flowing toward the ionosphere. Dipolarization and the SCW appear before ground onset, following one or more of these trigger waves. The so-called “explosive growth phase” occurs in association with explosive growth of the trigger waves soon after onset. Seven characteristic features of substorm onsets and expansions observed at CRRES are described. Among these are two stages of expansion. The first expansion stage is initiated by the trigger waves (ballooning) in the near-geosynchronous plasma sheet. Approximately 10 minutes later a second stage begins consistent with the arrival of earthward bulk flows emanating from a near-Earth X line. Near-geosynchronous substorm onsets can explain the observed increase in the occurrence rate of fast bulk flows earthward of its minimum value near X = −12 RE. Drift-Alfven ballooning also provides a possible causal link between observed reductions of the solar wind driver and substorm onsets.

Coupled electromagnetic and thermal modeling of microwave oven heating of foods.

Abstract: Temperature distributions from heating in a domestic microwave oven were studied by considering the coupling between the electromagnetics and heat transfer through changes in dielectric properties during heating Maxwell's equations for electromagnetics and the thermal energy equations are solved numerically using two separate finite-element softwares The coupling between the softwares was developed by writing special modules that interfaced these softwares at the system level Experimentally measured temperature profiles were compared with the numerical predictions The importance of coupling was evident when the properties changed significantly with temperature for low and high dielectric loss materials and more so for the high loss materials For moderate loss materials, when the properties do not change as much with temperature, coupled solutions lead to results very close to the results for the uncoupled solution

Mutual coupling compensation using subspace fitting

Abstract: The effects of an unknown mutual coupling is compensated for by estimating the coupling along with the direction of arrival (DOA) using a modified version of the noise subspace fitting (NSF) algorithm. It is possible to concentrate the NSF criterion regarding time coupling parameters, and the DOAs are obtained by a numerical search just as in the coupling free case. To evaluate the proposed method, the mutual coupling in a uniform linear array (ULA) of dipoles is calculated using fundamental electromagnetics. It is found that the effects of an unknown coupling can be reduced by estimating the coupling as well as the DOAs.

Designing for Product Sound Quality

Abstract: The meaning of product sound quality goal setting using metrics and jury testing noise control, noise reduction, and design for sound quality sources of prescribed motion - imbalance, cams, gears, chains and sprockets sources of prescribed forces - electromagnetics, airflow, combustion and impact structural response to excitation - single dof multi-dof response transmission between structures basics of sound radiation sound radiation by products and its measurement quality assurance using vibration.

Introduction to Genetic Algorithms in Electromagnetics

Abstract: This article is a tutorial on using genetic algorithms to optimize antenna and scattering patterns. Genetic algorithms are "global" numerical-optimization methods, patterned after the natural processes of genetic recombination and evolution. The algorithms encode each parameter into binary sequences, called a gene, and a set of genes is a chromosome. These chromosomes undergo natural selection, mating, and mutation, to arrive at the final optimal solution. After providing a detailed explanation of how a genetic algorithm works, and a listing of a MATLAB code, the article presents three examples. These examples demonstrate how to optimize antenna patterns and backscattering radar-cross-section patterns. Finally, additional details about algorithm design are given. >

A Simple Introduction to the Method of Lines

Abstract: The method of lines (MOL), a semianalytical procedure, is well known to experts in computational techniques in electromagnetics. The range of applications of the method has increased dramatically in the past few years; nevertheless, there is no introductory paper to initiate a beginner to the method. This paper illustrates the application of the MOL to solve Laplace's equation in rectangular and cylindrical coordinates. Two numerical examples are used to verify the procedure. The results obtained compare well with analytical solutions.

Wave–field reciprocity and optimization in remote sensing

Abstract: A unified approach to local optimization techniques and wave–field reciprocity as applied to constructing solutions to remote sensing, imaging and inversion problems in acoustic, elastic and electromagnetic wave theory is presented. The starting point is a system of linear, first–order partial differential equations in space–time of the class to which the indicated wave phenomena gives rise. For this system, three types of remote sensing problems — the inverse–source, the inverse–scattering, and the inverse–transducted–wave–field problems — are formulated, and the construction of their solutions via local optimization techniques is discussed. Emphasis is placed on iterative algorithms that are based on a guaranteed decrease in the mismatch between modelled and observed data at each update of the medium. Subsequently, the wave–field reciprocity theorems of the time–convolution and the time–correlation types are derived and their occurrence in the optimization procedures is discussed. Also, attention is paid to approximate methods, in particular to the Rayleigh–Gans–Born approximation. Approximations of this sort provide the means to invoke the method of preconditioning in the process of inverting the operator equations. ‘Exotic media’ (for example, chiral media in electromagnetics) are included in the analysis.

Electromagnetic Fields, Waves and Numerical Methods

Abstract: This book gives a complete overview of the classical electromagnetic theory, together with detailed insight in modern numerical methods for analysis of the problems in electromagnetics. Classical electromagnetic theory was developed in the 19th century, but due to the wide range of applications from electrical apparatus such as motors or heaters to telecommunications this subject is still very interesting. This book explains basic postulates and laws of the theory and its specialization to static and time-dependent problems. Special attention is given to utilization of computers in application of the modern numerical methods to solution of electromagnetic field problems.

Evaluating and expressing uncertainty in complex S-parameter measurements

Abstract: This paper presents methods for evaluating and expressing the uncertainty associated with complex S-parameter measurements. The methods are based on internationally recommended guidelines [1] with extensions to accommodate the complex nature of the measurands. The treatment of measurements of both one-port and multi-port devices is presented.

Design of a vehicular antenna for GPS/Iridium using a genetic algorithm

Abstract: In this paper, we describe a vehicular wire antenna, designed using a genetic algorithm that may be used for both the GPS and Iridium systems. It has right-hand circular polarization, near hemispherical coverage, and operates over the frequency band from 1225 to 1625 MHz. This antenna was simulated using the numerical electromagnetics code (NEC) and then fabricated and tested. The antenna consists of five copper tubing segments connected in series, has an unusually odd shape, and is very inexpensive. It fits in a volume approximately 10 cm/spl times/10 cm/spl times/15 cm, The input voltage standing wave ratio (VSWR) and circular polarization radiation patterns were computed and measured. The VSWR was under 2.2 at the design frequencies of 1225, 1575, and 1625 MHz. The gain varied by less than 12 dB for a 170/spl deg/ sector; it generally fell off near the horizon so the variation was less for 150/spl deg/ and 160/spl deg/ sectors. This new design process, which uses a genetic algorithm in conjunction with an electromagnetics code, produces configurations that are unique and seem to outperform more conventional designs.

An X wave transform

Abstract: Limited diffraction beams such as X waves can propagate to an infinite distance without spreading if they are produced with an infinite aperture and energy. In practice, when the aperture and energy are finite, these beams have a large depth of field with only limited diffraction. Because of this property, limited diffraction beams could have applications in medical imaging, tissue characterization, blood flow velocity vector imaging, nondestructive evaluation of materials, communications, and other areas such as optics and electromagnetics. In this paper, a new transform, called X wave transform, is developed. In the transform, any well behaved solutions to the isotropic-homogeneous wave equation or limited diffraction beams can he expanded using X waves as basis functions. The coefficients of the expansions can be calculated with the properties that X waves are orthogonal. Examples are given to demonstrate the efficacy of the X wave transform. The X wave transform reveals an intrinsic relationship between any well behaved solutions to the wave equation and X waves, including limited diffraction beams. This provides a theoretical foundation to develop new limited diffraction beams or solutions to the wave equation that may have practical usefulness.

Radio Frequency Radiation Dosimetry and Its Relationship to the Biological Effects of Electromagnetic Fields

Abstract: Preface. Acknowledgements. Introduction. Session A: Basics of Electromagnetics and Dosimetry. Chair: Y. Grigoriev. Session B: Dielectric Properties of Biological Tissue. Chair: C. Gabriel. Session C: Theoretical Dosimetry. Chair: O.P. Gandhi. Session D: Experimental Dosimetry. Chair: N. Kuster. Session E: Contact and Induced Currents. Chair: M. Israel. Session F: Response of Man and Animals I. Chair: E.R. Adair. Session G: Responses of Man and Animals II. Chair: J.A. D'Andrea. Session H: Applications of Dosimetry in Biology & Medicine. Chair: D. Miklavcic. Session I: Standards and Applications. Chair: J.M. Osepchuk. Session J: The Dosimetry Handbook. Chair: P.A. Mason. Appendix. Speakers. Participants. Official Photograph. Index.

Essentials of Electromagnetics for Engineering

Abstract: 1. Introduction 2. Some elements of vector analysis 3. The electrostatic field 4. The electrostatic potential 5. The transition towards Maxwell's equations for electrostatics 6. Electrostatic fields in material media 7. Electrostatic energy, electromechanical force, and capacitance 8. The Laplace and Poisson equations of electrostatics 9. Numerical solutions of Laplace and Poisson equations 10. Electric current 11. The magnetostatic field 12. The magnetostatic potentials 13. Inductance and magnetic stored energy 14. Magnetostatic fields in material media 15. Extension to electrodynamics 16. How Maxwell's equations lead to waves and signals 17. Important features of plane time-harmonic waves 18. Reflection and transmission of plane waves 19. Waveguides 20. Transmission lines 21. Selected topics in radiation and antennas Appendices.

A comparison of commercial software packages for microstrip antenna analysis

Abstract: Both computer power and software capabilities have increased substantially, and there are now a variety of general purpose software packages commercially available for the analysis and design of antennas and microwave components. Before the advent of such software, a common practice in industry and universities was to write custom computer codes for the solution of a specific antenna geometry. Although this situation led to steady progress in the development of improved numerical electromagnetics methods, as well as the nurturing of a generation of electromagnetics practitioners, it was a costly, slow, and inflexible approach. Today it is usually much more cost effective to acquire and use general purpose CAD packages capable of modeling a wide range of antenna geometries that may be of interest. Nevertheless, not all antenna CAD packages have the same capabilities or performance, and each may be best suited for a particular type of problem. We compare five commercial software packages for the analysis of several types of commonly used microstrip antennas. Factors including accuracy, speed of execution, setup time, and cost are presented. Measured impedance data is used as a standard for comparison, and results are also compared with custom full-wave moment method codes.