Book Review

J.L. NORMAN VIOLETTE ASSOCIATE EDITOR

EMC Analysis Methods and Computational Models

by

Frederick M. Tesche
Michel V. Ianoz
Torbjorn Karlsson

Publisher: John Wiley & Sons, Inc. New York, 1997
(623 pages)

This “meaty”, 623-page book is organized by starting with a Preface followed by five parts, Parts I - V. This review follows the same sequence.

PREFACE

The Preface provides a background of the progress through the years in numerical computation and applications to models to visualize electromagnetic interference and to assist in its mitigation. The usefulness of mathematical models is described as well as their limitations. Many past and present engineers and scientists involved in modeling and computation of electromagnetic (EM) phenomena are acknowledged in the PREFACE and ACKNOWLEDGMENTS sections of the book. Many topics pertaining to EM modeling and computation are described briefly as they are presented in the respective chapters in the book.

PART I  PRELIMINARIES

Chapter 1. Introduction to Modeling and EMC

Modeling of physical processes in general is presented as a useful tool for analysts and for use in EMC applications. Modeling in general is discussed and suggestions presented on various ways of how they may be used in studies and other aspects of EMC.

Topics developed in subsections of this chapter include the concept of modeling, the experimental and nonexperimental validation of models, and the building of models in electromagnetics.  An historical overview is provided on EMC modeling.  The classification of EMC problems is outlined and typical EMC problems amenable to modeling are described. Different types of signal waveforms and their frequency spectra encountered in EMC models are tabulated. The limits of modeling accuracy due to the complexity of practical EMI situations are described. The chapter text ends with a section that identifies users of modeling.

Chapter 2. System Decomposition for EMC Modeling

This chapter introduces electromagnetic (EM) topology to accomplish system decomposition into simple parts for EMC modeling. This is considered key to the application of any mathematical model representing system behavior. Analytical methods in EMC can be used throughout the planning, design, and construction phases of an electrical system. A flow-chart is provided to illustrate the overall role of modeling analysis in system development.

The need for EMC verification is usually required and performed by immunity and emission testing. A summary is provided of the use of analytical models including the need for understanding their limitations and user expectations.

The topological description of systems is illustrated in terms of constructing one or more Faraday shields (EM barriers) between an EMI source and potentially sensitive equipment.  Protective devices (filters, gaskets, surge suppressors, etc.) are needed at intended and other likely points of entry (POEs) through the shield. The basic technique of EM topology is illustrated diagrammatically. It is indicated that the topological design of a complex system is difficult to control and significant errors can occur in the analysis.

EM interaction (coupling) with the system must be determined to perform an approximate analysis of system response. This is developed with the EMI coupling process described with interaction sequence diagrams. Modeling accuracy and inherent errors are discussed.

PART II  LOW-FREQUENCY CIRCUIT MODELS

Chapter 3. Lumped-Parameter Circuit Models

This section describes the applicability of models when the physical dimensions of the system are much smaller than the wavelength of the disturbing (EMI) signal(s). The approach should be quite familiar to electrical engineers who can recall the concepts of circuit theory that are taught in typical undergraduate EE curricula. The models developed herein can be applied when interfering sources are connected directly to the victim circuit or when the victim circuit is located near the source and is excited by the EM fields produced by the source. Examples are presented of these types of conducted or radiated interference situations.

The use of Thevenin and Norton equivalent circuits is described to develop models where the sources of EMI are connected directly (hard-wired) to another circuit. Models for passive, linear, two-port circuit parameters are described with circuit equations and also in matrix format. The relationships between two-port impedance, admittance, chain parameters, and two-port active sources are described and tabulated, with the development extended to multiport networks.  Examples are provided of conducted disturbances in electrical power systems, and the generation of harmonic currents are described. The determination of the mains impedance is also described.

The disturbances in circuits induced by EM fields are described in terms of magnetic field coupling including weak-coupling approximations. Calculation techniques for mutual and self-inductance are presented. Electric field coupling is also described including weak-coupling approximations. Calculation techniques for mutual and self-capacitance are presented.

General field coupling is described where both electric and magnetic field coupling are active at low frequencies. This is followed by an example for determining crosstalk between two parallel traces on a PCB. General and specific methods are presented for reducing low-frequency interference.

A section describes disturbances caused by common ground returns. Part II ends with a section on the extension of circuit modeling to high frequencies.

PART III  HIGH-FREQUENCY AND BROADBAND COUPLING MODELS

Chapter 4. Radiation Models for Wire Antennas

At higher frequencies, where the EM field wavelength dimension becomes comparable to equipment dimensions, the low-frequency models become incresingly less accurate with increasing frequency. Essentially, the EM fields become wavelike and alternative modeling techniques are required. Solutions to Maxwell’s equations provide a more general description of the EM fields at both low and high frequencies. The details of radiation and scattering of EM energy from wire antennas at high frequencies are presented, with concentration on models that permit rapid calculations of antenna responses as opposed to the more accurate solutions that require considerably more computer resources.

The concepts are developed of the radiation of EM fields in the frequency domain. Radiation from elementary sources, electric and magnetic dipoles, extended sources, and center-fed wire antennas is presented. The solution of an integral equation (IE) is developed as a more general approach for determining the current distribution on a wire antenna. The Method of Moments (MoM) technique is illustrated to obtain an approximate solution for the IE. Other example calculations include dipole radiation in the presence of other bodies such as ground planes, in a parallel-plate region, in a cavity, near a sphere, and over an imperfectly conducting earth.  The evaluation of magnetic field components from the electric fields is illustrated using Maxwell’s equations.

The reception and scattering of EM fields in the frequency domain are described. Solutions to the electric field integral equations (EFIE) and the integro-differential equations in the time domain are outlined.

The singularity expansion method (SEM) is described as an extension of the IE solutions at complex frequencies. The natural (resonant) frequencies that characterize the frequency domain response of antennas and scatterers forms the basis for this method. A mathematical description of the SEM is provided with illustrative examples of SEM representations.

Chapter 5. Radiation, Diffraction, and Scattering Models for Apertures

This chapter addresses solutions to EM field leakage, or penetrations, through holes or other imperfections in a shield boundary. Techniques presented include scalar diffraction theory, Kirchhoff Approximation, Dirichlet and Neuman solutions, including Green’s function formulation. Since EM fields are vector quantities, general vector field diffraction is presented with irradiance patterns for rectangular and circular apertures illustrated.

The application of an integral equation for the tangential E and H fields in the aperture is presented to obtain a more accurate solution for the EM field penetration through an aperture. An example is presented of an aperture field calculation.

Radiation from extended antennas is outlined. Equivalent polarized electric and magnetic dipoles are presented as a method for determining low frequency approximation of radiation through apertures. Wideband and transient responses of apertures are illustrated.

PART IV  TRANSMISSION LINE MODELS

Chapter 6. Transmission Line Theory

The importance of transmission line theory and concepts are described for use in developing models for high frequency excitation where low frequency approximations become increasingly inaccurate. The many concepts presented include lumped and distributed parameters, two-conductor and multiconductor systems, transmission line and antenna mode responses, the telegrapher’s equation, the evaluation of line parameters, frequency domain responses, two-port and chain parameter representations for a two-wire line, line termination and reflection coefficient, line responses, validation of transmission line models, multiconductor line impedance and admittance matrices, and the “BLT” (Baum-Liu-Tesche) equation development for multiconductor lines. Time-domain transmission line responses are illustrated including time-harmonic excitation, nonsinusoidal traveling waves, and the transformation from the frequency domain to the time-domain. Numerical solutions are illustrated including Bergeron’s graphical solution in the time domain. A computer code called the Electromagnetic Transients Program (EMTP) is described briefly. The presentation of methods for determining line inductance and capacitance parameters conclude this detailed chapter.

Chapter 7.  Field Coupling Using Transmission Line Theory

This chapter discusses transmission line models and illustrates their use for describing some typical EMC problems. Three different approaches are introduced for describing the coupling of an external EM field to a line by applying transmission line theory:

(1) line excitation by incident magnetic flux linking the two line conductors, and incident electric flux terminating on the two conductors giving rise to distributed voltage and current sources on the line (Taylor approach).

(2) EM scattering process where tangential E-field along the conductors viewed as distributed voltage sources (Agrawal method).

(3) Line excitation only by incident B-field components giving rise only to distributed current sources on the line (developed by Rashidi).

The two-wire transmission line model is used to derive what are called the first and second telegrapher’s equations for lossless conditions, and the modification of the equations for a finitely  conducting wire and for a lossy medium surrounding the line.

Alternative forms of the telegrapher’s equations are presented including total and scattered voltage formulation. Numerical examples are provided of the two formulations. Solutions are provided for the line current and voltage and the load currents and voltages. Other extended applications of transmission line techniques are presented including frequency domain and transient responses.

A model is developed for a single line over a perfectly-conducting ground plane including line excitation from an EM scattering viewpoint.  A treatment of highly resonant structures  includes a single-wire line and an extension to multiconductor lines. Radiation from transmission lines is presented.

The analysis of transmission networks is illustrated including the development of the network BLT equation technique. Transmission lines with nonlinear loads are analyzed including the derivation of the Volterra integral equation. Examples are presented throughout this chapter.

Chapter 8. Effects of a Lossy Ground on Transmission Lines

This chapter extends the transmission line models discussed in Chapters 6 and 7 but includes the effects of a lossy earth serving as a return conductor. The telegrapher’s equation is derived and frequency and time domain solutions are presented for lossy conditions. Mathematically, the formulations are in terms of integral relationships for the E and H fields separated into excitation and scattered components. From these relationships the telegrapher’s equation is derived and boundary conditions applied. Per-unit length line parameters are derived and frequency and time domain representations are developed.

The remainder of the chapter illustrates numerous mathematical applications of lossy transmission line configurations and techniques with developments in the frequency and time domains.

Chapter 9. Shielded Cables

The introduction to this chapter states, regarding shielded cables:

“As such, one can define two distinct transmission lines: an external line having currents and charges flowing on the exterior of the cable, together with a possible ground-plane return, and an internal line consisting of the conductors inside the shield.”

It is postulated that EMI fields can excite the external transmission line, and if the shield is imperfect, some of the external currents and charges can penetrate through the shield and excite the internal line and thus cause an unwanted response.

Fundamentals of cable shield coupling are developed with transfer impedance and admittance defined based on an external and internal circuit formulation. Coupling through a solid tubular shield is derived and models for EM field penetration through braided shields are formulated. Penetrations of EM fields through single and multiple apertures are developed, as well as impedance and admittance parameters.  Graphical illustrations are provided for the variation of parameters with frequency. “Name-brand” models developed by Tyni, Demoulin, and Kley are presented and compared. The calculation of responses of a braided cable is illustrated.

High and low frequency models for cables with shield interruptions are presented, including the effects of cable connectors, pigtail terminations, and discontinuous shields.

Chapter 10. Shielding

This chapter discusses the principles of EM shielding and illustrates results from some of the simple models that can be used for predicting shielding performance. Shielding is presented as only one element of many that together create a complete protection system against EMI.

The general principles of shielding are presented including the properties of shielding materials and the impact of openings on shielding performance. Shielding of static electric and magnetic fields is presented, and then extended to time-varying fields. The concept of the eddy current shielding mechanism is discussed, whereby these currents produce E and H fields that oppose the fields incident on the conducting shield.

Skin depth and skin effect are described. Plane-wave shielding by a  metal plate of infinite extent, but of finite thickness, is developed. Other shielding topics covered include volumetric shields, shielding of time- harmonic fields, E and H field shielding effectiveness, shielding of transient EM fields, closed metallic mesh shields, shielding of non-plane wave fields, and shielding between two circular loops.

Overall Book Evaluation

This book presents progressive, detailed mathematical developments of a relatively advanced nature, at a level beyond the usual undergraduate engineering curriculum (exceptions acknowledged). The mathematical developments should be useful to a potential reader interested in solving problems in advanced electromagnetics and applying relevant  mathematical modeling and computational techniques. The book should be of interest for anyone interested in component and system response to conducted and radiated EMI for formulating EMC analysis and design. This also can be accomplished to some degree by reading this book and “get the bottom line”  without fully having to follow the details of the mathematical developments. It is recommended for practicing engineers, scientists, and others interested in indepth electromagnetic model analysis and computational techniques.

The book is also recommended as a text or reference book for an advanced senior or graduate level engineering course in electromagnetic computational analysis and modeling. An adequate number of interesting problems are provided at the end of each chapter, which reinforce the material in the text.

Reviewed by:

J.L. Norman Violette
Violette Engineering
Corporation (VECorp)
120 East Broad Street
Falls Church, VA 22046
TEL: (703) 532-1355
FAX: (703) 538-3810
email: enviolette@msn.com

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