Circuit Modeling for Electromagnetic Compatibility

308 Pages·2013·16.568 MB·English

by  Ian B. Darney

DESIGNING FOR COMPATIBILITY
Very simply, electromagnetic interference (EMI) costs money, reduces profits, and
generally wreaks havoc for circuit designers in all industries. This book shows
how the analytic tools of circuit theory can be used to simulate the coupling
of interference into, and out of, any signal link in the system being reviewed.
The technique is simple, systematic and accurate. It enables the design of any
equipment to be tailored to meet EMC requirements.
Every electronic system consists of a number of functional modules interconnected
by signal links and power supply lines. Electromagnetic interference can be
coupled into and out of every conductor. A review of the construction of the wiring
assemblies and the functions of the signals they carry will allow critical links to be
identified. Circuit modeling can be used to simulate the electromagnetic coupling
mechanism of each critical link, allowing its performance to be analyzed and
compared with the formal requirements. Bench testing during the development
of any product will allow any interference problem to be identified and corrected,
long before the manufactured unit is subjected to formal testing.
KEY FEATURES
• A fully outlined, systematic and dramatically simplified process of designing
equipment to meet EMC requirements.
• Focuses on simplifications which enable electrical engineers to singularly
handle EMC problems.
• Helps minimize time-to-market of new products and reduces the need for
costly and time-consuming modifications.
• Outlines how general purpose test equipment (oscilloscopes and signal
generators) can be used to validate and refine any model.
• Discusses how to use Mathcad or MATLAB® to perform analysis and
assessment.
ABOUT THE AUTHOR
Ian B. Darney was awarded a BSc degree in Electrical Engineering at the University
of Glasgow in 1960. He joined the Guided Weapons Division of British Aerospace
and worked on the circuit design of equipment for missiles, ground equipment,
submersibles, and spacecraft. After transferring to the Airbus Division he carried
out certification work associated with lightning indirect effects, electrostatics and
intrinsic safety. He was a member of the European Organisation for Civil Aviation
Equipment (EUROCAE) committee which defined the requirements for the
protection of aircraft from the indirect effects of lightning. Since his retirement,
he has continued to work as an EMC consultant, and has written two technical
papers and numerous magazine articles on EMC.
Circuit Modeling for
Electromagnetic Compatibility
Other titles in the series
Designing Electronic Systems for EMC (2011)
byWilliam G.Duff
Electromagnetic Measurementsin the Near Field, Second Edition (2012)
byPawel Bienkowski and Hubert Trzaska
Circuit Modeling for Electromagnetic Compatibility (2013)
byIan B. Darney
TheEMC Pocket Guide (2013)
byKenneth Wyatt and Randy Jost
Forthcoming titles in the series
EMC Essentials (2014)
byKenneth Wyatt and Randy Jost
Electromagnetic Field Standardsand Exposure Systems (2014)
byEugeniuszGrudzinski and Hubert Trzaska
Guide to EMC Troubleshooting andProblem-solving (2014)
byPatrick G.Andre´ and Kenneth Wyatt
Designing Wireless CommunicationSystems for EMC (2014)
byWilliam G.Duff
Circuit Modeling for
Electromagnetic Compatibility
EMC Series
Ian B. Darney
Edison, NJ
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The SciTech Series on Electromagnetic Compatibility
TheSciTechSeriesonElectromagneticCompatibilityprovidesacontinuouslygrowingbody
ofknowledgeinthelatestdevelopmentsandbestpracticesinelectromagneticcompatibility
engineering. EMC is a subject that has broadened its scope in the last 20 years to include
effects associated with virtually all electronic systems, ranging from the nanoscale to large
installations and from physical devices to distributed communications systems. Similarly,
EMC knowledge and practices have spread beyond the EMC specialist to a much wider
audience of electronic design engineers. Nolonger can ESD/EDI problems be addressed as
a solution to an unforeseen problem in a reactive response. Rather, design engineers can
modelandsimulate systemsspecifically torootoutthepotential forsucheffects.Similarly,
knowledge and practice from other engineering disciplines have become an integral part of
the subject of electromagnetic compatibility. The aim of this series is to provide this
broadening audience of specialist and non-specialist professionals and students books by
authoritative authors that are practical in their application but thoroughly grounded in a
relevanttheoreticalbasis.Thus,seriesbookshaveasmuchrelevanceinamodernuniversity
curriculum as they do onthe practicing engineer’s bookshelf.
Circuit Modeling for Electromagnetic Compatibility, EMC Series
Ian B. Darney
Understanding a problem often means focusing on the heart of the issue. That is what this
book does: it strips away the clutter in order to help develop an appreciation and
understanding of some of the core issues for EMC. Circuit Modeling for Electromagnetic
Compatibility demonstrates how powerful the simple models for lumped parameter, trans-
mission line, and the antenna can be. The origins of this book go back over 40 years and
emphasize thehugeamount thatcanbegarnered fromsimplified analytical approaches.Ian
Darney’s clear approach is that if you can simulate the observed response, you are a long
way toward solving the problem.
IanandIfirstspokeaboutthisbookaboutayearandahalfago,anditwasapparentthat,
havingspentasuccessfulcareerasanelectronicsystemsdesigner,hehadafirmintentionto
sharehiscareer’slearninginadistilledandaccessiblebook.Somepeoplemayfeelthattoo
much of the detail has been stripped away, but the vast majority of the engineers I have
shared this with have enjoyed both the technical underpinnings and Ian’s approach to
communicating it.
Ithinkthisisagreatcompanionbookforanyelectronicengineer’sbookshelf.Itwillhelp
non-EMC engineers get to grips with the core technology challenges and help EMC engi-
neersvisualizethedrivingmechanismsforsomeofthephenomenatheyareworkingwithon
a daily basis.
Alistair Duffy–Series Editor
2013

Contents
Preface xiii
Acknowledgments xvii
1 Introduction 1
1.1 Background 1
1.1.1 The need forEMC 1
1.1.2 Pragmatic approach 1
1.1.3 Academic approach 2
1.1.4 Managerial approach 2
1.1.5 Misleading concepts 2
1.1.6 Circuit modeling 3
1.1.7 Computations 3
1.1.8 Testing 3
1.1.9 Essence of the approach 4
1.2 Developing the model 4
1.2.1 Basic model 4
1.2.2 Parameter types 5
1.2.3 Derivation process 6
1.2.4 Composite conductors 7
1.2.5 Proximity effect 8
1.2.6 Electrical length 8
1.2.7 Distributed parameters 9
1.3 Intra-system interference 11
1.3.1 The signal link 11
1.3.2 Simulating the structure 11
1.3.3 Equivalent circuits 12
1.3.4 Conducted emission 12
1.3.5 Conducted susceptibility 13
vii
viii Contents
1.3.6 Voltage transformer 14
1.3.7 Current transformer 14
1.3.8 Representative circuit model 14
1.4 Inter-system interference 15
1.4.1 Dipole model 15
1.4.2 The virtual conductor 16
1.4.3 The threat voltage 17
1.4.4 Worst-case analysis 18
1.5 Transients 19
1.6 The importance of testing 20
1.7 Practical design techniques 21
1.8 System design 22
1.8.1 Guidelines 22
1.8.2 Top-down approach 23
1.8.3 Formal EMCrequirements 23
2 Lumped parameter models 25
2.1 Primitive capacitance 27
2.2 Primitive inductance 30
2.3 Duality of L and C 34
2.4 Loop parameters 35
2.5 Circuit parameters 38
2.5.1 Inductance 38
2.5.2 Capacitance 39
2.5.3 Maintaining duality 40
2.5.4 Resistance 41
2.5.5 Basic assumption 42
2.6 Twin-conductor model 42
2.7 Three-conductor model 45
2.8 Optimum coupling 49
2.9 Transfer admittance 52
2.10 Co-axial coupling 55
2.11 The ground plane 57
3 Other cross sections 61
3.1 Single composite conductor 62
3.2 The composite pair 67
3.3 The screened pair 74
Contents ix
4 Transmission line models 81
4.1 Single-T model 82
4.2 Triple-T model 86
4.3 Cross-coupling 89
4.4 Bench test models 94
5 Antenna models 101
5.1 The half-wave dipole 102
5.1.1 Radiated power 102
5.1.2 Powerdensity 104
5.1.3 Field strength 105
5.1.4 Powerreceived 106
5.2 The virtual conductor 107
5.3 The threat voltage 113
5.4 The threat current 117
5.5 Coupling via the structure 122
5.6 Radiation susceptibility 130
5.7 Radiated emission 132
6 Transient analysis 135
6.1 Time-step analysis 137
6.1.1 Basic concept 137
6.1.2 Basic equations 137
6.1.3 Series LCR circuit 138
6.1.4 Parallel LCRcircuit 140
6.2 Delay-line model 143
6.3 Line characteristics 149
6.4 Antenna-mode current 155
6.5 Radiated emission 161
6.5.1 Current linking the transformer 161
6.5.2 Line voltage 164
6.5.3 Source current and voltage 164
6.5.4 Radiated current 165
6.5.5 Cable losses 166
6.5.6 Line parameter measurements 167
6.6 Transient emission model 168