Showing papers on "Computational electromagnetics published in 1992"

Electromagnetic modeling of 3-D structures by the method of system iteration using integral equations

Abstract: A new approach for electromagnetic modeling of three‐dimensional (3-D) earth conductivity structures using integral equations is introduced. A conductivity structure is divided into many substructures and the integral equation governing the scattering currents within a substructure is solved by a direct matrix inversion. The influence of all other substructures are treated as external excitations and the solution for the whole structure is then found iteratively. This is mathematically equivalent to partitioning the scattering matrix into many block submatrices and solving the whole system by a block iterative method. This method reduces computer memory requirements since only one submatrix at a time needs to be stored. The diagonal submatrices that require direct inversion are defined by local scatterers only and thus are generally better conditioned than the matrix for the whole structure. The block iterative solution requires much less computation time than direct matrix inversion or conventional point...

EM programmer's notebook-benchmark plate radar targets for the validation of computational electromagnetics programs

Abstract: In February, 1989, a Computational Electromagnetics (CEM) validation measurement program was initiated by the Electromagnetic Code Consortium (EMCC), to fabricate and test several small radar cross-section (RCS) range models, in order to generate RCS reference data for validating existing and future codes. As part of the validation effort, the EMCG defined various sets of three- and two-dimensional targets. Measured data are presented here for five of the 3D plate targets. They are a wedge-cylinder plate, a wedge-plate cylinder, a plate cylinder, a 2*3.5 lambda flat plate, and a wedge-cylinder with a gap. >

Electromagnetic modeling of passive circuit elements in MMIC

Abstract: A spatial domain mixed-potential integral equation method is developed for the analysis of microstrip discontinuities and antennas of arbitrary shape. The algorithm is based on roof-top basis functions on a rectangular and triangular mixed grid and analytical evaluation of the quadruple moment integrals involved. The algorithm has been successfully implemented into an accurate, efficient, and versatile computer program. The numerical results agree with the measured ones very well. >

Optimizing electromagnetic devices combining direct search methods with simulated annealing

Abstract: Problems of optimization in computational electromagnetics are discussed with particular reference to the determination of the global minimum of practical objective functions. An optimizing environment is described which uses integral methods for calculating user-defined objective functions. Results are presented which combine stochastic and direct search techniques to find a satisfactory design optimum of practical problems. >

Global optimization methods for computational electromagnetics

Abstract: Both higher-order (pseudo)deterministic and zeroth-order probabilistic optimization methods have been analyzed and tested for solving the global optimization problems arising in computational electromagnetics. Previously recommended, but seemingly independent schemes (evolution strategies, simulated annealing, Monte Carlo iteration) have been unified into a robust general method: the global evolution strategy (GES). Regularization techniques, the stability of solutions, and nonlinear phenomena are shown to be topics closely related to global optimization and inverse problems. The speed of convergence is evaluated for different optimization methods. A real-world application (from nuclear magnetic resonance and magnetic resonance imaging) demonstrates the favorable behavior of GES in the context of the finite element method. >

Innovation in Maxwell's Electromagnetic Theory: Molecular Vortices, Displacement Current, and Light

Abstract: Preface Introduction 1. The background to Maxwell's electromagnetic theory 2. Mechanical image and reality in Maxwell's electromagnetic theory 3. The elaboration of the molecular-vortex model 4. The introduction of the displacement current 5. The origin of the electromagnetic theory of light 6. Beyond molecular vortices Conclusion Appendices.

Review of current status and trends in the use of integral equations in computational electromagnetics

Abstract: A summary of the state-of-the-art in the formulation and numerical solution of integral equations in electromagnetics is presented. Following a brief summary of the method of moments, database and software requirements are given for specifying and numerically representing geometries and their electrical characteristics and excitation. While concentrating on the formulation of problems in the frequency domain, issues involved in time domain formulations are are also briefly summarized. Basic principles involved in the formulation of integral equations, including the use of Green's functions and symmetry to simplify the solution procedure, are presented. A class of basis and testing functions is defined which subsumes many of those in common use, and their application to compuational electromagnetics is outlined. Finally, matrix solution methods are summarized. For each of the issues considered, an indication of possible new directions in computational electromagnetics is also given.

A general purpose Maxwell solver for the extraction of equivalent circuits of electronic package components for circuit simulation

Abstract: The electromagnetic modeling of electronic packages is discussed, and a general-purpose Maxwell solver is presented for deriving equivalent circuits of various components of a package that can be inserted in a SPICE-type circuit simulation program to investigate the electrical performance of the package. The solver is based on the finite-difference-time-domain (FDTD) algorithm. Its usefulness is illustrated by applying it to a number of representative problems. >

Three dimensional circuit oriented electromagnetic modeling for VLSI interconnects

Abstract: A general approach for modeling 3-D layout geometries is presented. In particular, the partial-element equivalent circuit (PEEC) technique has been used successfully to model interconnect structures for chips and packages. The technique, which is circuit based, permits the electrical modeling of arbitrary 3-D geometries and allows 3-D transmission line properties to be analyzed. Recently, the technique has been extended to include retardation and dielectric layers. The authors have experimented with the use of the asymptotic waveform evaluation (AWE) approach to speed up the solution of the resulting circuit equations. >

The finite-element modeling of three-dimensional time-domain electromagnetic fields in strongly inhomogeneous media

Abstract: An efficient and accurate finite-element method is presented for computing transient electromagnetic fields in three-dimensional configurations containing arbitrarily inhomogeneous media that may be anisotropic. To obtain accurate results with an optimum computational efficiency, both edge and Cartesian elements are used for approximating the spatial distribution of the field. The efficiency and the storage requirements of the method are further optimized by choosing an irreducible implicit formulation, by solving the resulting system of algebraic equations in terms of the time-dependent expansion coefficients iteratively, and by using an incomplete LU-decomposition for preconditioning. A method is described for imposing the divergence condition in a weighted sense. The theory discussed was implemented in the FEMAXT code. >

Finite Element Modelling of a Synchronous Machine : Electromagnetic Forces and Mode Shapes

Abstract: Manufacturers in electrical machinery are becoming highly interested in the reduction of noise and vibrations; this is due to the increasing awareness of the problem in some industrial and military applications : one of the main causes of noise production in electrical machines is resonance between the electromagnetic force and the stator. Two fundamental steps are of importance to deal with the acoustic noise reduction problem: -study and assessment of the vibration behaviour of the stator (resonant frequencies, mode shapes....); -analysis of the electromagnetic force distribution. The objective of this paper is to report an advancement of the above works using the finite element method. The results of all previous steps are mentionned and discussed below. For this work we have used a permanent magnet synchronous machine.

Geophysical interpretation using integral equations

Abstract: Part 1 General matters concerning integral equations: demonstration of an integral equation solution classification of integral equations numerical solution. Part 2 Elements of electrostatics and potential theory: differential representation of electrical potential integral representation of electrical potential primary current electrode volume distribution of simple sources surface distribution of simple sources surface distribution of double sources. Part 3 Electrical methods: resistivity of rocks resistivity method magnetometric resistivity mis-a-la-masse method surface polarization induced polarization self-potential electrical anisotropy. Part 4 Elements of magnetrostatics: integral representation of magnetic potential volume distribution of simple poles surface distribution of simple poles volume distribution of dipoles. Part 5 Magnetic methods: magnetic properties of rocks high-susceptibility models demagnetization and low-susceptibility models numerical applications effect of remanence. Part 6 Electromagnetic methods: boundary value problems for electromagnetic fields Green's dyadics for electromagnetic boundary value problems volume integral equations for 3-dimensional electromagnetic field volume integral equations for 2-dimensional electromagnetic fields surface integral equations for electromagnetic fields integral equation solution for electromagnetic fields in a thin conductor model. Part 7 Integral formulae for elastic wave fields in an anisotropic medium integral formulae for elastic wave fields in an isotropic medium separation of elastic wave fields into a compressional and a rotational mode integral formulae for acoustic wave fields in the frequency domain integral formulae for acoustic wave fields in the time domain applications. Appendices: Green's function for scalar potential in a two-layer half-space Green's function for scalar potential in a half-space with a vertical contact Green's function for scalar potential in an anisotropic half-space electric Green's dyadic for a half-space below the ground surface.

Experimental modeling of electromagnetic wave scattering from an ocean surface based on chaotic theory

Abstract: Electromagnetic wave scattering from an ocean surface has a long history ofbeing modeled as a stochastic process. In this paper, we demonstrate experimentally that the random nature of electromagnetic scattering may be described by a chaotic phenomenon. Data used in this paper were collected by two different radar systems at different sites. Our analysis is divided into three parts: correlation dimension analysis, local divergence analysis and predictive modeling. All three tests positively point to a conclusion that chaos may be a suitable phenomenon to describe electromagnetic wave scattering from an ocean surface.

Electromagnetic borehole fields in a layered, dipping‐bed environment with invasion

Abstract: Electromagnetic modeling of an induction sonde (1–100 kHz) in a dipping‐bed environment is a 3-D problem. The capability for such an analysis is necessary for interpretation of oil‐well logs in offshore environments where most holes are deviated. 3-D geometrical effects require vector field analysis. The method accounts for transverse magnetic mode (TM) coupling arising from surface charges deposited by eddy currents passing through bed boundaries. If borehole and invasion effects are included, the only available rigorous analytical methods are finite elements or finite‐difference techniques. These approaches require large‐scale computing. In contrast, our method is approximate and is an extension of the geometrical‐factor theory and Born approximation. The variational method does not require matrices and is numerically simpler than the more rigorous finite element method. The method uses a new electric field vector integral equation developed by Chew. The formulation accounts for low‐frequency behavior a...

An Absorbing Boundary Condition Based on Anechoic Absorber For EM Scattering Computation

Abstract: A novel absorbing boundary condition (ABC), to be used with finite difference and finite element electromagnetic radiation and scattering problems is described. It is based on anechoic chamber absorber foam geometry, with specified complex permittivity and permeability. The advantage of this absorbing boundary is that it prevents reflections from much wider incident angles than currently used lattice termination conditions. Since incident waves need not be normal to this boundary for absorption, the boundary can be placed much closer than previously possible. This new type of ABC can be used to absorb scattered waves in a local sense, so the electrical size of the scattering object does not effect the distance from it to the ABC. Since even a modest decrease in the required separation distance yields a huge savings in the number of required matrix elements for three dimensional geometries, this novel ABC may greatly improve the general applicability of computational electromagnetics.

mu -synthesis of an electromagnetic suspension system

Abstract: The authors discuss the mu -synthesis of an electromagnetic suspension system. The issue of modeling a real physical electromagnetic suspension system is discussed. A nominal model as well as a set of models in which the real system is assumed to reside is derived. Different model structures and possible model parameter values are fully employed to determine unstructured additive plant perturbation, which directly yield the uncertainty weighting. Based on the set of plant models, the robust performance control objectives are defined. Using the mu -Analysis and Synthesis Toolbox, use is made of the D-K iteration approach for the controller design. Implementing the controller with a digital signal processor mu PD77230, experiments are carried out to evaluate the robust performance of this design. It was shown that the closed-loop system with the mu -controller achieves not only nominal performance and robust stability, but also robust performance. >

Electromagnetic modeling of 3-D sources over 2-D inhomogeneities in the time domain

Abstract: A numerical method is presented by which the transient electromagnetic response of a two‐dimensional (2-D) conductor, embedded in a conductive host rock and excited by a rectangular current loop, can be modeled. This 2.5-D modeling problem has been formulated in the time domain in terms of a vector diffusion equation for the scattered magnetic induction, which is Fourier transformed into the spatial wavenumber domain in the strike direction of the conductor. To confine the region of solution of the diffusion equation to the conductive earth, boundary values for the components of the magnetic induction on the ground surface have been calculated by means of an integral transform of the vertical component of the magnetic induction at the air‐earth interface. The system of parabolic differential equations for the three magnetic components has been integrated for 9 to 15 discrete spatial wavenumbers ranging from 10-7 to 4×10-2m-1 using an implicit homogeneous finite‐difference scheme. The discretization of the...

Calculation of impulse current distributions and magnetic fields in lightning protection structures-a computer program and its laboratory validation

Abstract: A circuit model and an ad hoc computer program were set up to evaluate electromagnetic interference in the vicinity of protective structures struck by lightning. This program permits the evaluation of the impulsive magnetic fields by calculating the impulse current distribution in different parts of such structures. It also allows the evaluation of the electromagnetic interference induced on susceptible victim circuits to which electric equipment may be connected. To validate the approach, a series of impulse tests was performed in the laboratory on conductive structures designed to highlight the features of the program and to make evident the dependence of the impulse current distributions on some particular phenomena that need simplified modeling, such as the effect of induced or return currents through the ground. >

Low-frequency computational electromagnetics for antenna analysis

Abstract: An overview of computational methods for modeling the low-frequency electromagnetic characteristics of antennas is given. Presented first is a brief analytical background that forms the basis for numerically solving low-frequency antenna problems using the method of moments. Next discussed are extensions to modeling perfectly conducting objects in free space, followed by a consideration of some computational issues that affect model accuracy, efficiency, and utility. A variety of representative applications is given to illustrate various aspects of modeling and capabilities that are currently available. A fairly extensive bibliography is included. >

Grid decoupling in finite element solutions for Maxwell's equations

Abstract: Certain finite-element discretization methods used in time-domain electromagnetic modeling reduce to a type of finite-difference method when applied on a regular mesh. The form of this underlying finite-difference method is unusual; it consists of two decoupled grids, rotated 45 degrees from the original finite element mesh. >

A coupled thermal magnetic model for high frequency transformers. I. Model formulation and material properties

Abstract: A novel model for analyzing high-frequency transformers is presented. The model is based on the simultaneous solution of the coupled, nonlinear thermal and electromagnetic equations. The modeling and assumptions used to derive the governing equations are explained. A set of integrodifferential constraints are developed to apply the proper input voltage and output impedance to the transformer windings. Next, a method of modeling the magnetic material properties as a function of temperature and magnetic flux density is given. A novel technique for modeling the complex reluctivity of the soft-ferrite core material permits a time-harmonic transformation of the electromagnetic equations. This eliminates the need to step through time while maintaining the effects of hysteresis losses. A quasi-steady formulation of the heat-conduction equation eliminates the time dependence of the thermal problem. >

Symmetry properties of the scattering matrix in 3-D electromagnetic modeling using the integral equation method

Abstract: Modeling large three-dimensional (3-D) earth conductivity structures continues to pose challenges. Although the theories of electromagnetic modeling are well understood, the basic computational problems are practical, involving the quadratically growing requirements on computer storage and cubically growing computation time with the number of cells required to discretize the modeling body.

Parallel computing and its impact on computational electromagnetics

Abstract: It is noted that massively parallel, distributed memory computers will provide the increases in computing performance needed to solve the largest problems in computational electromagnetics. The authors describe such a system, covering its architecture, performance, and programming in relation to a model problem drawn from low-frequency magnetics. The results from this model problem are used to estimate the computing power required in different areas of computational electromagnetics. Finally, the issue of ease of programming, including software issues such as parallel libraries, is discussed. >

Recent developments in transient magneto-structural integrated analysis for fusion applications

Abstract: Three different numerical approaches modeling the mutual field-structure interactions during transient electromagnetic events are presented. The application of these approaches to simple plate models simulating flexible conducting components of fusion devices shows that magnetic damping is encountered when coupling effects between, eddy currents and plate motion are taken into account. This damping increases with the applied magnetic field, modifying the mechanical behavior. It is noted that the complexity of electromagnetomechanical modeling can be overcome by the use of an integrated design/analysis system (currently under development) that allows the combined use of different-purpose computer codes. >

Finite-difference algorithms for the time-domain Maxwell's equations - A numerical approach to RCS analysis

Abstract: The applications of two CFD-based finite-difference methods to computational electromagnetics are investigated In the first method, the time-domain Maxwell's equations are solved using the explicit Lax-Wendroff scheme and in the second method, the second-order wave equations satisfying the Maxwell's equations are solved using the implicit Crank-Nicolson scheme The governing equations are transformed to a generalized curvilinear coordinate system and solved on a body-conforming mesh using the scattered-field formulation The induced surface current and the bistatic radar cross section are computed and the results are validated for several two-dimensional test cases involving perfectly-conducting scatterers submerged in transverse-magnetic plane waves

A simple and accurate approach to model the coupling of vertical and horizontal dipoles in layered media

Abstract: A simple and accurate approach to electromagnetic modeling the coupling of a vertical electric dipole (VED) and a horizontal electric dipole (HED) in layered media is presented. In this approach, the scalar potential Green's functions have been properly defined so that the desired form of the MPIE (mixed potential integral equation) can be used. The approach has been used to analyze the problem of VED and HED in a dielectric slab. The spatial Green's functions have been efficiently computed using the complex image technique. The approach developed is useful for the modeling of a wide class of printed structures that involve both VED and HED in layered media. >

Numerical Computation of Electromagnetic Fields

Abstract: Computational electromagnetics has become an important field both for academic research and for the engineering design of electrical devices. It is an involved region of applied mathematics where advanced mathematical methods are applied to paritcular questions of electrical engineering. In this talk, some basic computational methods for time harmonic fields in scattering problems are discussed. The emphasis will be on wave function series and integral representations of the fields which, alone with the finite element and difference methods, still play an important role in the practical field computation.