electromagnetic shielding

Electromagnetic Shielding SALVATORE CELOZZI RODOLFO ARANEO GIAMPIERO LOVAT Electrical Engineering Department ‘‘La Sapienza’’ University Rome, Italy IEEE Press A JOHN WILEY & SONS, INC., PUBLICATION Electromagnetic Shielding WILEY SERIES IN MICROWAVE AND OPTICAL ENGINEERING KAI CHANG, Editor Texas A&M University A complete list of the titles in this series appears at the end of this volume. Electromagnetic Shielding SALVATORE CELOZZI RODOLFO ARANEO GIAMPIERO LOVAT Electrical Engineering Department ‘‘La Sapienza’’ University Rome, Italy IEEE Press A JOHN WILEY & SONS, INC., PUBLICATION Copyright # 2008 by John Wiley & Sons, Inc. 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TK454.4.M33C45 2008 621.3–dc22 2008006387 Printed in the United States of America 10987654321 CONTENTSCON Contents Preface xi 1 Electromagnetics behind Shielding 1 1.1 Definitions 1 1.2 Notation, Symbology, and Acronyms 3 1.3 Basic Electromagnetics 4 1.3.1 Macroscopic Electromagnetism and Maxwell’s Equations 4 1.3.2 Constitutive Relations 6 1.3.3 Discontinuities and Singularities 9 1.3.4 Initial and Boundary Conditions 11 1.3.5 Poynting’s Theorem and Energy Considerations 11 1.3.6 Fundamental Theorems 13 1.3.7 Wave Equations, Helmholtz Equations, Electromagnetic Potentials, and Green’s Functions 15 1.4 Basic Shielding Mechanisms 18 1.5 Source Inside or Outside the Shielding Structure and Reciprocity 18 References 19 2 Shielding Materials 21 2.1 Standard Metallic and Ferromagnetic Materials 21 2.2 Ferrimagnetic Materials 27 2.3 Ferroelectric Materials 28 2.4 Thin Films and Conductive Coatings 30 2.5 Other Materials Suitable for EM Shielding Applications 32 2.5.1 Structural Materials 32 2.5.2 Conductive Polymers 32 v 2.5.3 Conductive Glasses and Transparent Materials 33 2.5.4 Conductive (and Ferromagnetic or Ferrimagnetic) Papers 33 2.6 Special Materials 33 2.6.1 Metamaterials and Chiral Materials 33 2.6.2 Composite Materials 36 2.6.3 Nanomaterials 37 2.6.4 High-Temperature Superconductors 37 References 38 3 Figures of Merit for Shielding Configurations 42 3.1 (Local) Shielding Effectiveness 42 3.2 The Global Point of View 45 3.3 Other Propos als of Figures of Merit 46 3.4 Statistical Methods 50 3.5 Energy-Based, Content-Oriented Definition 52 3.6 Performance of Shielded Cables 53 References 53 4 Shielding Effectiveness of Stratified Media 55 4.1 Electromagnetic Plane Waves: Definitions and Properties 55 4.2 Uniform Plane Waves Incident on a Planar Shield 58 4.2.1 Transmission-Line Approach 58 4.2.2 The Single Planar Shield 61 4.2.3 Multiple (or Laminated) Shields 66 4.3 Plane Waves Normally Incident on Cylindrical Shielding Surfaces 67 4.4 Plane Waves against Spherical Shields 74 4.5 Limits to the Extension of the TL Analogy to Near-Field Sources 75 References 84 5 Numerical Methods for Shielding Analyses 87 5.1 Finite-Element Method 89 5.2 Method of Moments 99 5.3 Finite-Difference Time-Domain Method 110 5.4 Finite Integration Technique 119 5.5 Transmission-Line Matrix Method 124 5.6 Partial Element Equivalent Circuit Method 127 5.7 Case Study: Scattering from a Perfectly Conducting Enclosure with a Rectangular Aperture 134 References 137 6 Apertures in Planar Metal Screens 144 6.1 Historical Background 145 6.2 Statement of the Problem 146 6.3 Low-Frequency Analysis: Transmission through Small Apertures 147 vi CONTENTS 6.4 The Small Circular-Aperture Case 148 6.5 Small Noncircular Apertures 154 6.6 Finite Number of Small Apertures 155 6.7 Rigorous Analysis for Apertures of Arbitrary Shape: Integral Equation Formulation 157 6.8 Rules of Thumb 160 References 161 7 Enclosures 164 7.1 Modal Expansion of Electromagnetic Fields inside a Metallic Enclosure 165 7.2 Oscillations inside an Ideal Source-Free Enclosure 168 7.3 The Enclosure Dyadic Green Function 169 7.4 Excitation of a Metallic Enclo sure 172 7.5 Damped Oscillations inside Enclosures with Lossy Walls and Quality Factor 173 7.6 Apertures in Perfectly Conducting Enclosures 175 7.6.1 Small-Aperture Approximation 176 7.6.2 Rigorous Analysis: Integral-Equation Formulation 178 7.6.3 Aperture-Cavity Resonances 180 7.7 Small Lo ading Effects 183 7.8 The Rectangular Enclosure 184 7.8.1 Symmetry Considerations 187 7.9 Shielding Effectiveness of a Rectangular Enclosure with a Circular Hole 188 7.9.1 External Sources: Plane-Wave Excitation 189 7.9.2 Internal Sources: Electric and Magnetic Dipole Excitations 192 References 198 8 Cable Shielding 200 8.1 Transfer Impedance in Tubular Shielded Cables and Aperture Effects 201 8.2 Relationship between Transfer Impedance and Shielding Effectiveness 206 8.3 Actual Cables and Harnesses 207 References 208 9 Components and Installation Guidelines 210 9.1 Gaskets 210 9.2 Shielded Windows 214 9.3 Electromagnetic Absorbers 215 9.4 Shielded Connectors 216 9.5 Air-Ventilation Systems 216 CONTENTS vii 9.6 Fuses, Swi tches, and Other Similar Components 217 References 217 10 Frequency Selective Surfaces 219 10.1 Analysis of Periodic Structures 220 10.1.1 Floquet’s Theorem and Spatial Harmonics 220 10.1.2 Plane-Wave Incidence on a Planar 1D Periodic Structure 222 10.1.3 Plane-Wave Incidence on a Planar 2D Periodic Structure 223 10.2 High- and Low-Pass FSSs 225 10.3 Band-Pass and Band-Stop FSSs 228 10.3.1 Center-Connected Elements or N-Pole Elements 229 10.3.2 Loop-Type Elements 230 10.3.3 Solid-Interior-Type Elements 230 10.3.4 Combinations and Fractal Elements 231 10.4 Degrees of Freedom in Designing FSSs 231 10.5 Reconfigurable and Active FSSs 232 10.6 FSSs and Circuit Analog Absorbers 234 10.7 Modeling and Design of FSSs 235 References 236 11 Shielding Design Guidelines 241 11.1 Establishment of the Shielding Requirements 242 11.2 Assessment of the Number and Types of Functional Discontinuities 243 11.3 Assessment of Dimensional Constraints and Nonelectromagnetic Characteristics of Materials 244 11.4 Estimation of Shielding Performance 245 References 246 12 Uncommon Ways of Shielding 247 12.1 Active Shielding 247 12.2 Partial Shields 252 12.3 Chiral Shielding 255 12.4 Metamaterial Shielding 256 References 260 Appendix A Electrostatic Shielding 263 A.1 Basics Laws of Electrostatics 264 A.2 Electrostatic Tools: Electrostatic Potential and Green’s Function 266 A.3 Electrostatic Shields 270 A.3.1 Conductive Electrostatic Shields 270 A.3.2 Dielectric Electrostatic Shields 274 A.3.3 Aperture Effects in Conductive Shields 279 References 281 viii CONTENTS [...]... health rather than EMC Electromagnetic shielding also is used to prevent sensitive information from being intercepted, that is, to guarantee communication security Electromagnetic shielding is not the only remedy for such purposes Some sort of electromagnetic shielding is almost always used in apparatus systems to reduce their electromagnetic emissions and to increase their electromagnetic immunity... manuscript Salvatore Celozzi Rodolfo Araneo Giampiero Lovat Rome, Italy July 2007 CHAPTER ONE Electromagnetics behind Shielding Shielding an electromagnetic field is a complex and sometimes formidable task The reasons are many, since the effectiveness of any strategy or technique aimed at the reduction of the electromagnetic field levels in a prescribed region depends largely upon the source(s) characteristics,... [8] E J Rothwell and M J Cloud Electromagnetics Boca Raton: CRC Press, 2001 [9] S A Schelkunoff ‘‘On teaching the undergraduate electromagnetic theory.’’ IEEE Trans Educ., vol E-15, pp 15–25, Feb 1972 20 ELECTROMAGNETICS BEHIND SHIELDING [10] C.-T Tai ‘‘On the presentation of Maxwell’s theory.’’ Proc IEEE, vol 60, no 8, pp 936– 945, Aug 1972 [11] J Van Bladel Singular Electromagnetic Fields and Sources... when common terms are adopted in a technical context, different definitions exist In electromagnetics shielding effectiveness (SE) is a concise parameter generally applied to quantify shielding performance However, a variety of standards are adopted for the measurement or the assessment of the performance of a given shielding structure Unfortunately, they all call for very specific conditions in the... substantially reduces the effect of electric or magnetic fields on one side thereof, upon devices or circuits on the other side Electromagnetic Shielding by Salvatore Celozzi, Rodolfo Araneo and Giampiero Lovat Copyright # 2008 John Wiley & Sons, Inc 1 2 ELECTROMAGNETICS BEHIND SHIELDING This definition is restrictive because it implicitly assumes the presence of a ‘‘victim.’’ The definition is also based... arbitrariness Another definition [2] of electromagnetic shielding that is even more restrictive is: [A] means of preventing two circuits from electromagnetic coupling by placing at least one of the circuits in a grounded enclosure of magnetic conductive material The most appropriate definition entails a broad view of the phenomenon: [A]ny means used for the reduction of the electromagnetic field in a prescribed... reference to shape, material, and grounding of the shield is necessary to define its purpose In general, electromagnetic shielding represents a way toward the improvement of the electromagnetic compatibility (EMC, defined as the capability of electronic equipment or systems to be operated in the intended electromagnetic environment at design levels of efficiency) performance of single devices, apparatus,... subject of this type Standards proliferation is a real problem for almost any engineer, and the field of electromagnetic shielding does not represent an exception to this modernday ‘‘disease.’’ The chapters are organized as follows: First some introductory remarks are presented on the electromagnetics of shielding (Chapter 1), followed by a description of the arsenal of conventional and less-conventional... ¼  Iþ  rr Gðr; r0 Þ; k2 ð1:42Þ and the free-space magnetic dyadic Green function Gm is Gm ðr; r0 Þ ¼ rGðr; r0 Þ Â I; where I is the identity 3 Â 3 tensor ð1:43Þ 18 ELECTROMAGNETICS BEHIND SHIELDING 1.4 BASIC SHIELDING MECHANISMS EM shielding may be pursued by any of the following main strategies, or by a combination of them:  Interposition of a ‘‘barrier’’ between the source and the area (volume)... CONTENTSCII Preface This book might have been titled Introduction to Electromagnetic Shielding, since every chapter, that is to say, every section, could well be the subject of a book Thus the goal of this book is to provide a first roadmap toward a full understanding of the phenomena at the core of the complex and fascinating world of electromagnetic shielding The book is organized in twelve chapters and three . Equations, Electromagnetic Potentials, and Green’s Functions 15 1.4 Basic Shielding Mechanisms 18 1.5 Source Inside or Outside the Shielding Structure and Reciprocity 18 References 19 2 Shielding. Constraints and Nonelectromagnetic Characteristics of Materials 244 11.4 Estimation of Shielding Performance 245 References 246 12 Uncommon Ways of Shielding 247 12.1 Active Shielding 247 12.2. Celozzi Rodolfo Araneo Giampiero Lovat Rome, Italy July 2007 xii PREFACE CHAPTER ONE Electromagnetics behind Shielding Shielding an electromagnetic field is a complex and sometimes formidable task. The reasons