Electromagnetics Explained: A Handbook for Wireless/ RF, EMC, and High-Speed Electronics

375 Pages·2002·5.32 MB·English

ELECTROMAGNETICS
EXPLAINED
A HANDBOOK FOR WIRELESS/RF, EMC, AND
HIGH-SPEED ELECTRONICS
Ron Schmitt
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Library of Congress Cataloging-in-Publication Data
Schmitt, Ron.
Electromagnetics explained: a handbook for wireless/RF, EMC, and high-speed
electronics / Ron Schmitt.
p. cm.
Includes bibliographical references and index.
ISBN 0-7506-7403-2 (hc.: alk. paper)
1. Electronics. 2. Radio. 3. Electromagnetic theory. I. Title.
TK7816 .S349 2002
621.381—dc21 2001055860
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ACKNOWLEDGMENTS
First and foremost, I want to thank my wife, Kim Tripp. Not only did
she give me love and patient support, she also typed in the references
and drew many of the figures. For this, I am greatly indebted. I also want
to thank my family, and particularly wish to thank my mother, Marion
Schmitt, who provided the cover art and the drawings of hands and
human figures in Chapter 3.
I am very thankful for the help of Dr. Laszlo Kish, for being a col-
league and a friend, and most of all, for being my mentor. He had the
patience to answer so many of my endless questions on electromagnet-
ics, quantum physics, and physics in general. My bosses at SRD also
deserve special mention: Mr. Carl Freeman, President; Dr. Greg Grillo,
Vice President; and Dr. Jeremy Hammond, Director of Engineering
Systems. Thanks to my friends at SRD for the most enjoyable years of
my career.
This book wouldn’t have been possible without the help of the great
people at Newnes, particularly Candy Hall, Carrie Wagner, Chris Conty,
Jennifer Packard, and Kevin Sullivan. Joan Lynch was instrumental to
the success of this book by connecting me with Newnes. The readers of
EDN, whose interest motivated me to write this book, deserve acknowl-
edgment, as do my friends at Nortel Networks, where I wrote the first
article that started this whole process.
Many people provided me with technical assistance in the writing.
Roy McCammon pointed out that I didn’t understand electromagnetics
as well as I thought I did, especially in regard to surface waves in trans-
mission lines. Dr. Keith Hardin provided me with his wonderful thesis
on asymmetric currents and their relation to common-mode radiation.
Dr. Clayton Paul examined my shielding plots and confirmed their cor-
rectness. Dr. Mark Rodwell provided me with insights on the state-of-
the-art in ultra-high-speed electronics. Dr. Paul Horowitz told me about
the strange problems involving cable braids at high frequencies. Dr.
Thomas Jones and Dr. Jeremy Smallwood gave answers to questions
regarding static electricity. Dr. Istvan Novak provided information on
xv
xvi ACKNOWLEDGEMENTS
decoupling in high-speed digital systems. Dr. Allan Boardman answered
several of my questions regarding electromagnetic surface waves. Dr.
Tony Heinz helped me answer some questions regarding transmission
lines in the infrared and beyond. I also wish to thank Nancy Lloyd,
Daniel Starbird, and Julie Frost-Pettengill.
I want to thank all the people who reviewed my work: Don McCann,
John Allen, Jesse Parks, Dr. Neil Comins, Les French, Dr. Fred Irons, Dr.
Dwight Jaggard, and my anonymous reviewer at EDN. Finally, I extend
thanks to everyone who made other small contributions and to anyone
I may have forgotten in this list.
PREFACE
This book is the result of many years of wondering about and research-
ing the conceptual foundations of electromagnetics. My goal was to
write a book that provided the reader with a conceptual understanding
of electromagnetics and the insight to efficiently apply this under-
standing to real problems that confront scientists, engineers, and tech-
nicians. The fundamental equations that govern electromagnetic
phenomena are those given to us by James Clerk Maxwell, and are com-
monly known as Maxwell’s equations. Excepting quantum phenomena,
all electromagnetic problems can be solved from Maxwell’s equations.
(The complete theory of electromagnetics, which includes quantum
effects, is quantum electrodynamics, often abbreviated as QED.) How-
ever, many people lack the time and/or mathematical background
to pursue the laborious calculations involved with the equations of
electromagnetism. Furthermore, mathematics is just a tool, albeit a
very powerful tool. For many problems, exacting calculations are not
required. To truly understand, develop, and apply any branch of science
requires a solid conceptual understanding of the material. As Albert
Einstein stated, “Physics is essentially an intuitive and concrete science.
Mathematics is only a means for expressing the laws that govern phe-
nomena.”* To this end, this book does not present Maxwell’s equations
and does not require any knowledge of these equations; nor is it required
for the reader to know calculus or advanced mathematics.
The lack of advanced math in this book, I’m sure, will be a tremen-
dous relief to most readers. However, to some readers, lack of math-
ematical rigor will be a negative attribute and perhaps a point for
criticism. I contend that as long as the facts are correct and presented
clearly, mathematics is not necessary for fundamental understanding,
but rather for detailed treatment of problems. Moreover, everyday scien-
tific practice shows that knowing the mathematical theory does not
*Quoted in A. P. French, ed., Einstein: A Centenary Volume,Cambridge, Mass.: Harvard
University Press, 1979, p. 9.
xi
xii PREFACE
ensure understanding of the real physical “picture.” Certainly, mathe-
matics is required for any new theories or conclusions. The material that
I cover has been addressed formally in the literature, and readers are
encouraged to pursue the numerous references given throughout. Con-
ceptual methods for teaching the physical sciences have long been in use,
but I think that the field of electromagnetics has been neglected and
needs a book such as this. If relativity, quantum theory, and particle
physics can be taught without mathematics, why not electromagnetics?
As inspiration and guide for my writing I looked to the style of writing
in works such as The Art of Electronics by Paul Horowitz and Winifred
Hill, several books by Richard Feynman, and the articles of the maga-
zine Scientific American.
SUGGESTED AUDIENCE AND GUIDE FOR USE
This text is mainly intended as an introductory guide and reference for
engineers and students who need to apply the concepts of electromag-
netics to real-world problems in electrical engineering. Germane disci-
plines include radio frequency (RF) design, high-speed digital design,
and electromagnetic compatibility (EMC). Electromagnetism is the
theory that underlies all of electronics and circuit theory. With circuit
theory being only an approximation, many problems, such as those of
radiation and transmission line effects, require a working knowledge of
electromagnetic concepts. I have included practical tips and examples
of real applications of electromagnetic concepts to help the reader bridge
the gap between theory and practice.
Taking a more general view, this book can be utilized by anyone learn-
ing electromagnetics or RF theory, be they scientist, engineer, or tech-
nician. In addition to self-study, it could serve well as a companion text
for a traditional class on electromagnetics or as a companion text for
classes on RF or high-speed electronics.
Those readers interested in RF or electromagnetics in general will find
the entire book useful. While Chapter 1 serves as a good introduction
for everyone, Chapters 2, 3, and 4 cover the basics and may be unnec-
essary for those who have some background in electromagnetics. I direct
those readers whose discipline is digital design to focus on Chapters 1,
7, 8, and 12. These four chapters cover the important topics that relate
to digital circuits and electromagnetic compatibility. EMC engineers
should also focus on these four chapters, and in addition will probably
be interested in the chapters that cover radiation (Chapter 5), shielding
(Chapter 9), and antennas (Chapter 11). Chapter 6, which covers rela-
PREFACE xiii
tivity and quantum theory, is probably not necessary for a book like this,
but I have included it because these topics are fascinating to learn about
and provide a different perspective of the electromagnetic field.
PARTING NOTES
I gladly welcome comments, corrections, and questions, as well as sug-
gestions for topics of interest for possible future editions of this book.
As with any writing endeavor, the publishing deadline forces the author
to only briefly address some topics and omit some topics all together.
I am also considering teaching one- or two-day professional courses cov-
ering selected material. Please contact me if such a course may be of
interest to your organization. Lastly, I hope this book is as much a plea-
sure to read as it was to write.
Ron Schmitt, [email protected]
Orono, Maine
July 2001
CONTENTS
PREFACE xi
ACKNOWLEDGMENTS xv
1 INTRODUCTION AND SURVEY OF THE
ELECTROMAGNETIC SPECTRUM 1
The Need for Electromagnetics 1
The Electromagnetic Spectrum 3
Electrical Length 8
The Finite Speed of Light 8
Electronics 9
Analog and Digital Signals 12
RF Techniques 12
Microwave Techniques 16
Infrared and the Electronic Speed Limit 16
Visible Light and Beyond 18
Lasers and Photonics 20
Summary 21
2 FUNDAMENTALS OF ELECTRIC FIELDS 25
The Electric Force Field 25
Other Types of Fields 26
Voltage and Potential Energy 28
Charges in Metals 30
The Definition of Resistance 32
Electrons and Holes 33
Electrostatic Induction and Capacitance 34
Insulators (Dielectrics) 38
Static Electricity and Lightning 39
The Battery Revisited 45
Electric Field Examples 47
Conductivity and Permittivity of Common Materials 47
v