ELECTROMAGNETICS EXPLAINED A HANDBOOK FOR WIRELESS/RF, EMC, AND HIGH-SPEED ELECTRONICS Ron Schmitt An imprint of Elsevier Science Amsterdam Boston London Oxford New York Paris San Diego San Francisco Singapore Sydney Tokyo Newnes is an imprint of Elsevier Science. Copyright © 2002 by Elsevier Science (USA) All rights reserved. No part of this publication may be reproduced, stored in a retrieval system, or trans- mitted in any form or by any means, electronic, mechanical, photocopying, record- ing, or otherwise, without the prior written permission of the publisher. Recognizing the importance of preserving what has been written, Elsevier Science prints its books on acid-free paper whenever possible. 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 British Library Cataloguing-in-Publication Data A catalogue record for this book is available from the British Library. The publisher offers special discounts on bulk orders of this book. For information, please contact: Manager of Special Sales Elsevier Science 225 Wildwood Avenue Woburn, MA 01801-2041 Tel: 781-904-2500 Fax: 781-904-2620 For information on all Elsevier Science publications available, contact our World Wide Web home page at: http://www.newnespress.com 10 9 8 7 6 5 4 3 2 1 Printed in the United States of America Other titles in the EDN Series for Design Engineers Analog and Digital Filter Design, Second Edition, by Steve Winder 0-7506-7547-0, Paperback, 512 pgs., $59.99 Practical RF Handbook, Third Edition, by Ian Hickman 0-7506-5369-8, Paperback, 304 pgs., $39.99 Power Supply Cookbook, Second Edition, by Marty Brown 0-7506-7329-X, Paperback, 336 pgs., $39.99 Radio Frequency Transistors, Norman Dye and Helge Granberg 0-7506-7281-1, Paperback, 320 pgs., $49.99 Troubleshooting Analog Circuits, by Robert A. Pease 0-7506-9499-8, Paperback, 217 pgs., $34.99 The Art and Science of Analog Circuit Design, edited by Jim Williams 0-7506-7062-2, Paperback, 416 pgs., $34.99 Introducing the BOOKSTORE The Bookstore offers you: (cid:1)Hundreds of great technical books by engineers for engineers (cid:1) Monthly drawings for FREE books (cid:1) Specials offers & discount pricing (cid:1) FREE sample chapters Visit the Bookstore at www.ednmag/bookstore.com 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