Title: Electromagnetic Compatibility Engineering
Author: Henry Ott
Publisher: John Wiley, 2009
Henry Ott is one of the true pioneers of EMC education at the professional level, and his widely read book Noise Reduction Techniques in Electronic Systems (1976, 2nd edition 1988) has served as an entry point for many engineers in our field. Mr. Ott began his latest offering by contemplating a third edition to this venerable text, but the changes and additional material became so extensive that it grew into a new one. The author has taught professional EMC courses for many decades, gaining a vast experience that adds considerable depth and clarity to the text because in explaining the material, he also answers the many “what about?” and “what if?” questions that his students have posed over the years. He also explicitly dispels many of the myths of EMC that he has heard along the way.
Mr. Ott retains the philosophy found in his earlier works that although precise solutions to real-world EMC problems are seldom reached by mathematical calculation, an understanding of functional dependence of the various parameters involved is highly valuable for the practicing engineer. Equations are given for simple cases where a closed form solution exists, and they subsequently are graphed to give the reader a feel for the parametric variation. Further, electromagnetic phenomena are modeled by lumped element circuits where possible to give insight more easily to engineers who are generally more familiar with circuit concepts. This approach leads to a text that is highly practical in nature. The book offers an abundance of specific EMC design practices, but the reader is provided sufficient background and insight to understand why they work and how they can be applied to actual situations.
The author divided the material in the text into two parts: the first ten chapters dedicated to the theory of EMC, and the last eight presenting the application of the principles to EMC design. The first chapter gives basic principles, motivating examples of EMI problems, and a fairly detailed exposition of commercial regulations and military standards. The second chapter discusses coupling to cables, primarily for electrically short cables. Chapter 3 covers grounding techniques in ac power distribution, in signal transmission, and in systems. It also discusses ground loops and some mitigation methods. Chapter 4 describes the use of balanced signal transmission which is becoming increasingly popular and filtering. In the fifth chapter, the electrical behavior of various passive components including ferrites and their non-idealities are examined. It is here that transmission line theory is given, although it is used in the fourth chapter to explain decoupling filters. Basic shielding theory is presented in the sixth chapter. Schelkunoff’s approach is used to show that, except for very low frequency magnetic fields, direct penetration of electromagnetic waves through a shield wall is not an issue. Some basic equations for the shielding effectiveness of apertures are given along with a description of the properties of seams formed between mating parts. A vital feature is the emphasis on the importance of providing adequate contact pressure between the two pieces that form the seam. Throughout the second half of the chapter, the concept – crucial to the design of effective shields, that the shield must provide a low-impedance with a minimum of discontinuities for the surface current induced by an impinging field – is emphasized. Chapter 7 discusses contact protection and the switching of inductive loads. The eighth and ninth chapters characterize various sources of random noise found in passive and active devices along with the classic technique for calculating the overall noise in a system formed by cascading blocks. The first half of the text ends with chapter 10 where the grounding of digital circuits is examined with an eye to minimizing the noise voltage induced in the ground system.
Chapter 11 begins the EMC applications half of the book with a detailed examination of digital circuit power distribution. The relatively wideband spectrum of the transition pulses drawn through the power supply leads of digital logic devices are discussed, and a particularly valuable section points out the potentially deleterious parallel resonances that occur when capacitors of different sizes are placed in parallel. The twelfth chapter covers radiated emissions from digital circuits, decomposing them into the two mechanisms, differential mode and common mode. The characterizations used are for radiating structures that are somewhat smaller than a wavelength, but the design principles gained by examining parametric dependence are effective even at higher frequencies. Conducted emissions are discussed in Chapter 13 with an emphasis on switch-mode power supplies. Power line filters are also covered with a wealth of practical information on their application and mounting. Chapter 14 is devoted to product immunity from RF radiation and transients. Audio rectification of RF is explained, but unlike some of the author’s previous work, the role of resonances in exacerbating it is absent. The chapter continues with a thorough survey of the devices and their application for protecting power and signal lines from transients. Attention is paid to devices for high-speed digital lines where the quiescent shunt impedance of the device must be very high. Electrostatic discharge (ESD) is covered in Chapter 15 with mitigation techniques for both grounded and ungrounded products. Some of the most crucial elements in product design for EMC are the printed-circuit boards which are the focus of Chapters 16 and 17. A myriad of critical decisions must be made on layout, power and ground plane sectioning, and layer stack up, and these chapters give invaluable practical guidance on these issues. The difficult task of designing PCB containing mixed analog and digital signals to achieve signal integrity and product compliance is directly addressed with attention to the tradeoffs that come into play. In keeping with the author’s practical bent, the final chapter (18) gives a variety of techniques of pre-compliance testing that can be done in a design lab to diagnose and solve problems without paying for time in a certified EMC measurement lab. The use of various probes and receivers along with a kit of mitigation devices that are valuable for troubleshooting are described.
Four appendices are used to house additional information on the decibel, the behavior of low-frequency magnetic fields inside a shield wall, dipoles, and the powerful concept of partial inductance. Another appendix highlights ten common design mistakes that raise the level of emissions from a product.
The text is “intended primarily for the practicing engineer who is involved in the design of electronic equipment or systems” and that target is well met. But it also has sufficient clarity and depth to be used in an EMC undergraduate course. The extensive use of lumped element models will benefit students who are almost always more comfortable with circuits than with electromagnetics. For a one semester course, the instructor would have to choose a subset of the text, but the linkages are such that this could be done fairly easily. In fact, drafts of this book were used in the EMC course at the University of Michigan Dearborn and feedback was incorporated into the final product. The author supplies over 250 end-of-chapter problems that can be used to test and enhance student knowledge. A final appendix provides the answers to each one.
The overall impression of the text is one of thoroughness and practicality, presented in a particularly lucid style. With this latest book, Mr. Ott maintains his standing in the top rank of EMC authors and educators. This rare text possesses the simultaneous qualities of accessibility for the novice EMC engineer, even at the undergraduate student level, while providing sufficient depth to benefit a more experienced practitioner. It is destined to become a classic.
Thomas Jerse has over 30 years experience with Hewlett-Packard and Boeing in solving EMI problems both at the circuit and systems level, and has earned a Ph.D. in EMC from the University of Kentucky. He presently holds dual positions as Professor of Electrical Engineering at The Citadel and Associate Technical Fellow of the Boeing Company. EMC
|Author Henry Ott Receives
Prestigious PROSE Award
Congratulations to Henry Ott whose latest book is the recipient of the prestigious 2009 PROSE Award! The PROSE Awards were created by the Association of American Publishers to recognize books, journals and electronic products that best exemplify a sound contribution to professional and scholarly publishing, maintaining both the highest editorial standards and the highest standards of design and production consistent with the objectives of the project. The 2009 PROSE Awards received a record-breaking 441 entries – more than ever before in its 34-year history – from more than 60 professional and scholarly publishers across the country. This makes Mr. Ott’s award particularly noteworthy!