Title: Electromagnetic Shielding
Authors: Salvatore Celozzi, Rodolfo Araneo,
and Giampiero Lovat
Publisher: Wiley Interscience, 2008
Print ISBN: 9780470055366
Online ISBN: 9780470268483
This book presents electromagnetic shielding from a theoretical point of view. Each chapter devotes significant space to outline the underlying electromagnetic theory of the particular subject that the chapter addresses. Towards the end of the book, there are chapters devoted to more application oriented subjects. Therefore, this book is recommended if you need to address or understand shielding from theoretical fundamentals. The theoretical treatments are not exhaustive, but they provide a good introduction. There are extensive references in each of the chapters.
The book is divided into 12 chapters and three appendices. The chapter titles are as follow: 1) Electromagnetics behind shielding, 2) Shielding materials, 3) Figures of merit for shielding configurations, 4) Shielding effectiveness of stratified media, 5) Numerical methods for shielding analyses, 6) Apertures in planar metal screens, 7) Enclosures, 8) Cable shielding, 9) Components and installation guides, 10) Frequency selective surfaces, 11) Shielding guidelines, and 12) Uncommon ways of shielding. The appendices titles are: a) Electrostatic shielding, b) Magnetic shielding, and c) Standards and measurements methods.
The first chapter provides a good discussion of Maxwell’s equations, reciprocity theorem, equivalence principles, electromagnetic potentials, and Green functions; in essence, the kind of fundamental theory you would expect surrounding Maxwell’s equations. The second chapter discusses materials suitable for shielding. This is an interesting topic overall because there are new materials coming out on a regular basis from different manufacturers. The chapter provides an overview of off the shelf materials commonly used for shielding. Chapter 3 discusses the different ways of how to measure shielding effectiveness and other figures of merit to measure shielding. Chapter 4 addresses the application of Maxwell equations as the fields propagate through inhomogeneous media and then derives formulations for shielding effectiveness. In order to develop analytical expressions, only planar, cylindrical, and spherical geometries are considered. Numerical methods for shielding analyses are considered in Chapter 5 where an overview of FEM, FDTD, moment methods, TLM, and PEEC are considered. The treatment of these numerical techniques is at the introductory level only, but an actual example, or application, is discussed at the end of the chapter.
Chapter 6 and all subsequent chapters shift direction by starting to apply the subjects of the previous chapters to specific shielding issues; such as apertures, enclosures, cabling, etc. These are probably the concepts that are of most interest to EMC engineers. Chapter 6 tries to address the concept of leakage through an aperture, using again analytical approaches that are suitable for small apertures and lower frequencies. Apertures may be of arbitrary shapes. Likewise, in chapter 7, spherical, cylindrical, and rectangular enclosures are most suitable for studying since the vector eigenfunctions can be determined analytically and from which the Green functions (electric and magnetic) can be more easily derived. For example, towards the end of the chapter the resonant modes of a rectangular enclosure are discussed along with its shielding effectiveness. Apertures in enclosures (another EMC common topic) are theoretically addressed for the case where the enclosure is perfectly conducting. The chapter also discusses loading effects.
A brief discussion of cable shielding (via the concept of transfer impedance) is discussed in chapter 8 together with its relationship to shielding effectiveness; while chapter 9 discusses, also briefly, gaskets and electromagnetic absorbers. Frequency selective surfaces are discussed in chapter 10. These surfaces are obtained by means of periodic conductive structures (elements or apertures) in either one or two dimensions which given a specific geometry can act as filters. The treatment of such surfaces in the chapter is well done and it is probably the chapter I personally like best. Chapter 11 discusses some simple design guidelines for shielding effectiveness and chapter 12 discusses “active” shielding methodologies by using certain mitigation techniques to decrease the effect of other electric or magnetic fields. EMC