by Bruce Archambeault, Omar M. Ramahi,
and Colin Brench
Reviewed by
James L. Drewniak
Electromagnetic Compatibility Laboratory
University of Missouri-Rolla
Each of the authors of EMI/EMC Computational Modeling Handbook have a combination of many years of EMC (at IBM and Digital) as well as numerical electromagnetic modeling experience that results in a unique and useful presentation of this subject. As the authors remind the reader many times throughout, an EMC problem is minimally comprised of a noise source, unintended EMI antenna, and a parasitic path that couples energy from the noise source to the EMI antenna. The source is typically a high-speed digital IC, and the EMI antenna might be attached cables, or slots and apertures in a shielding enclosure. In practice, anticipating these two aspects of a potential EMI problem is much easier than the coupling path. The coupling path is related to layout features and may be parasitic inductance, capacitance, or a common impedance, and can be very difficult to anticipate at the design stage. Consequently, productively using numerical electromagnetic modeling to reduce EMI/EMC risk at the design stage can be challenging.
Numerical electromagnetic modeling is relatively mature, with many commercial codes available, and can result in good answers to well-defined problems. However, defining an EMI/EMC problem is in general an inexact art that typically requires both modeling as well as good EMC experience. The authors combine many years of industry EMC experience in shipping high-speed digital products, together with expertise that they have acquired in applying numerical modeling to product EMC design to provide the reader with valuable insight into productively using numerical modeling for EMC design.
The intended audience of the book is practicing engineers that may not be experts at numerical modeling, as well as more experienced modeling people that are seeking guidance on applying modeling to product design. I think that it is also an invaluable resource for graduate students that may be focusing on fundamental numerical modeling algorithms and issues to gain exposure to a new and growing area of application for these methods. The objectives of the book are to provide a rudimentary understanding of the common numerical electromagnetic modeling methods, and more significantly insight and guidance for incorporating them into the EMC design process. As such, the authors do not intend that it will be a comprehensive treatment on any particular numerical modeling method.
The book briefly reviews the basics of the three common numerical electromagnetic modeling methods, finite-difference time-domain (FDTD), finite element (FEM), and integral equation (method of moments MOM) formulations with some emphasis on FDTD. The critical issues in numerical modeling are determining the essential features that must be modeled, how to model them, and at what level of detail to result in a good and useful answer. In EMC design, ascertaining these very necessary details are typically difficult, and these are the issues on which the authors focus. The authors provide a good understanding of what can reasonably be expected and achieved in practical EMC design, basic modeling concepts, and how to use numerical modeling for understanding fundamental coupling physics, as well as for layout and design.
Chapter 1 is a brief introduction to EMI/EMC modeling, and the three common modeling methods. Chapter 2 is an overview of only the essential electromagnetic theory and basic “equations of motion” that are used later in the chapters on the individual modeling methods.
The three common, full-wave numerical electromagnetic modeling approaches, FDTD, MOM, and FEM are presented in Chapters 3, 4, and 5, respectively. In each case, only the essentials for acquiring a basic understanding of these methods are given. FDTD is a logical choice to present first since it is by far the easiest to understand of the three, as well as widely useful for EMI/EMC problems, and robust. The authors give the basics of the algorithm from a differential equation perspective, meshing, time-stepping, and absorbing boundaries. An alternative approach to understanding the basic algorithm is from the integral form of Maxwell’s equations that I particularly like because it gives a clear understanding of the FDTD method in terms of the underlying physics. The reader is referred to one of the references (A. Taflove, Computational Electrodynamics: The FDTD Method).
The MOM is presented in Chapter 4. Complete volumes are devoted to this subject, and the technical literature is vast on the MOM and applications. In the spirit of their original objectives, the authors have presented this difficult subject in a simple and straight-forward manner with Pocklington’s integral equation, i.e., MOM applied to wire geometries. The treatment is brief, and more-or-less one-dimesional, but adequate for a basic understanding. A further advantage of the choice in introducing MOM in this fashion is that a mature and commercially available MOM code (NEC) is largely wire-based.
The finite element method is presented in Chapter 5. The FEM presentation proceeds from a variational formulation and minimization of a quadratic functional, and may leave an inexperienced reader confused. An alternative path to the final algorithm is via a weak formulation (see J.N. Reddy, An Introduction to the Finite Element Method). I like this approach because a one-dimensional formulation is easily understandable. The 2D overview of triangular patch basis functions presented in Chapter 5 does give the reader a feeling for the solution approximation and meshing.
Chapters 6, 7, and 8 are at the heart of this book. The consistent theme emphasized in these chapters is “what and where to model” for EMI/EMC design. The reader is left with a good understanding of what is achievable in applying numerical modeling to EMC design, and how to approach and construct models that can lead to useful results. The treatment is a reflection of the authors extensive experience using modeling in their own work at IBM and Digital. Chapter 6 discusses anticipating and modeling the EMI coupling, as well as the noise source. Guidance in choosing a suitable technique, FDTD, FEM, or MOM for particular types of problems is also given.
Chapter 7 discusses creation of EMI/EMC models and details a number of examples including common-mode radiation from cables being driven against a shielding enclosure, excitation of heatsinks by an IC, and apertures in a shield. Inherent in these examples is insight into how EMI/EMC modeling can be used in developing better designs. For example, one configuration discussed details the effects of coupling through a slot in an enclosure to an attached cable. Slots inevitably result in low-cost PC enclosures as a result of cost-effective attempts to seal unused expansion ports. The example demonstrates developing a model to understand the coupling effects between the source, aperture, and attached cable. The result is a clear indication that the EMI problem is dominated by the source coupling to the aperture and provides direction on where attention should be focused in mitigating this problem, i.e., a ferrite sleeve on the attached cable is a waste of a good part for this particular case.
Chapter 8 is a more detailed continuation of Chapter 7, and focuses specifically on examples of multi-stage modeling for PCB level coupling to perforations in a shielding enclosure and coupling to an attached cable, antenna impedance important for I/O filter design, test site modeling, and basic PCB level modeling. The PCB level modeling example demonstrates the use of numerical modeling for developing an understanding of fundamental EMI coupling physics. The geometries can be relatively simple, but the resulting design concepts are powerful. Practicing EMC engineers commonly draw general design conclusions based on their experience with prototype or production hardware. This hardware is complex, and it is easy to draw incorrect conclusions regarding fundamental noise and coupling processes in the trial-and-error process of shipping products. Numerical EMI/EMC modeling is a powerful tool for developing an understanding of fundamental concepts, and experienced EMC engineers are well-versed in translating these to design.
Chapter 9 discusses model validation that provides good insight for engineers not experienced with modeling. Some very helpful caution is given regarding comparing radiated EMI measurements on a functioning product that are inherently not well controllable, with modeling results. Chapter 10 is a brief over-view on geometries that are representative of high-speed digital design aspects that may be suitable for numerical modeling. From the perspective of a practicing EMC engineer, this provides direction on what can realistically be expected from numerical modeling, as well as problems on which to investigate and compare commercially available tools. From the standpoint of the numerical modeling community, these problems represent some goals for which to strive, i.e., demonstrating (in particular through well-controlled measurements) modeling approaches for problems of interest to practicing EMC engineers.
Overall, I found this to be a good book that achieves the author’s stated goals very well, and I recommend it, in particular for practicing EMC engineers and numerical modelers. As I was reading the book and noting the aspects that I particularly liked or did not, I found that most of my criticisms were a matter of personal preference, and not fundamental disagreements with the treatment or presentation of topics. I would have liked to see more details in the examples that would allow the user to reproduce the author’s results. While this is certainly more appropriate to research papers published in the referenced technical literature, it is important for those less experienced with modeling to initially have targets at which to shoot. Since the first author is taking a leading role in the EMC community through the IEEE EMC Society Technical Committee 9 (Computational Electromagnetics) in advancing the state of the art, and developing standard EMI/EMC modeling problems with proven results, a future addition might include this.
Application of numerical modeling in EMC design is relatively recent, and I consider this book the first stage of a “work in progress”. The authors do not propose that this book is in any sense completed or concluded. I anticipate that this book will be updated and expanded periodically as the field progresses and grows.
Editor's Note: Many thanks to Jim Drewniak for providing this book review as a guest Associate Editor. Jim's experience in the field of EMI/EMC computational modeling is evident in this thorough book review and is surely appreciated by our readers. Jim may be reached at phone 573-341-4969 or email at drewniak@ee.umr.edu.