Electromagnetic Measurements in the Near Field

232 Pages·2011·2.145 MB·English

by  Pawel Bienkowski, Hubert Trzaska

ELECTROMAGNETIC MEASUREMENTS IN THE NEAR FIELD
This book is devoted to the specific problems of electromagnetic field
(EMF) measurements in the near field and to the analysis of the main
factors which impede accuracy in these measurements.
Starting with a thorough look at the fundamental engineering principles,
the book focuses on careful, accurate design of systems to measure in
the near field and on analyzing likely system errors. It details the factors
that limit near field EMF measurements including:
INTERNAL EXTERNAL
• thermal stability • field integration
• frequency response • mutual couplings between a
• dynamic characteristics probe and primary/secondary
• susceptibility EMF sources
• directional pattern
deformations
The book also includes a guide to testing the parameters declared by an
EMF meter manufacturer to ensure the measurements are accurate, as
well as how designers of equipment can reconsider the near field when
designing and testing.
Electromagnetics in the Near Field is addressed to a wide range of
specialists in biology, medicine, labor safety, environmental protection,
metrologists, and EMF meter designers.
ABOUT THE AUTHORS
Pawel Bienkowski is affiliated with the EM Environment Protection Lab at the
Technical University of Wroclaw, Poland where he researches electromagnetic
compatibility and electromagnetic field measurements and standards. He is
the author or co-author of over 100 publications and over 20 patents.
Hubert Trzaska is a Professor in the EM Environment Protection Lab
at the Technical University of Wroclaw, Poland where he researches
electromagnetic field measurements and standards. He is a Charter Member
of the Bioelectromagnetic Society and is the author or co-author of over 300
publications and over 50 patents.
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E
LECTROMAGNETIC
M
EASUREMENTS IN THE
N F
EAR IELD
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THE SCITECH SERIES ON ELECTROMAGNETIC COMPATIBILITY
Series Mission
This book series provides a continuously growing body of knowledge by incorpo-
rating underlying principles with best practices in electromagnetic compatibil-
ity engineering. It reflects modern developments of the last quarter century for
an ever-broadening audience. With a practical real-world emphasis, books bene-
fit non-specialist engineers and students as well as EMC veterans. Books are
written by recognized authorities in their field, with every manuscript thor-
oughly vetted by members of the EMC Editorial Board and additional qualified
advisors. The publisher applies high quality production processes to each publi-
cation and sets prices for the budgets of working professionals and students.
Editorial Advisory Board
Alistair Duffy, Series Editor, DeMonfort University, United Kingdom
Karol Aniserowicz, Bialystok University of Technology, Poland
Keith Armstrong, Cherry Clough Consultants, United Kingdom
Christos Christopoulos, University of Nottingham, United Kingdom
Andy Drozd, ANDRO Computational Solutions, U.S.A
Bill Duff, Applied Technology Institute, U.S.A
Dick Ford, Naval Research Lab (retired), U.S.A
Erping Li, National University of Singapore, Singapore
Andy Marvin, University of York, United Kingdom
Antonio Orlandi, University of L’Aquila, Italy
Howard Reader, University of Stellenbosh, South Africa
Vesna Roje, University of Split, Croatia
Bob Scully, NASA, U.S.A
Andrew Walters, Defence Science and Technology Organization, Australia
Books in the Series
Bienkowski and Trzaska – Electromagnetic Measurements in the Near Field
Duff – Design of Electronic Systems for EMC
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E
LECTROMAGNETIC
M
EASUREMENTS IN THE
N F
EAR IELD
Pawel Bienkowski
Hubert Trzaska
Second Edition
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Published by SciTech Publishing, Inc.
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Contents
Preface . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .vii
Preface to the Second Edition . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ix
Acknowledgments. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . xi
Chapter 1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1
Chapter 2 The Near Field and the Far Field. . . . . . . . . . . . . . . . . . . . . . . . . . 11
2.1 An EMF Generated by a System of Currents . . . . . . . . . . . . . . . . . . . . . . . . 11
2.2 The Far Field and the Near Field. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14
2.3 EMF from Simple Radiating Structures . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19
Chapter 3 EMF Measurement Methods . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27
3.1 E, H, and S Measurement . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28
3.2 Temperature Rise Measurements. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33
3.3 SAR Measurement. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 40
3.4 Current Measurements. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 41
Chapter 4 Electric Field Measurement . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 51
4.1 Field Averaging by a Measuring Antenna. . . . . . . . . . . . . . . . . . . . . . . . . . . 52
4.2 Influence of Fields from beyond a Probe Measuring Band. . . . . . . . . . . . . . 55
4.3 Mutual Interaction of the Measuring Antenna and the Field Source. . . . . . . 69
4.4 Changes in the Probes’ Directional Pattern. . . . . . . . . . . . . . . . . . . . . . . . . . 74
4.5 E-Field Probe Comparison. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 80
4.6 Comments and Conclusions. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 85
Chapter 5 Magnetic Field Measurement. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 89
5.1 The Sizes of the Measuring Antenna. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 89
5.2 Frequency Response of the Magnetic Field Probe . . . . . . . . . . . . . . . . . . . . 92
5.3 Directional Pattern Alternations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 95
5.4 Measurement Accuracy vs. Antenna Distance from Radiation Source. . . . 100
5.5 Magnetic Field Probe with a Loop Working above Its Self-Resonant
Frequency . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 105
5.6 Comments and Conclusions. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 109
Chapter 6 Power Density Measurement . . . . . . . . . . . . . . . . . . . . . . . . . . . . 113
6.1 Power Density Measurement Methods . . . . . . . . . . . . . . . . . . . . . . . . . . . . 113
6.2 Power Density Measurement Using the Antenna Effect. . . . . . . . . . . . . . . 122
6.3 Conclusions and Comments. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 128
v
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VI ELECTROMAGNTIC MEASUREMENTS IN THE NEAR FIELD
Chapter 7 Directional Pattern Synthesis. . . . . . . . . . . . . . . . . . . . . . . . . . . . 133
7.1 A Probe Composed of Linearly Dependent Elements . . . . . . . . . . . . . . . . 134
7.2 Spherical Radiation Pattern of an E/H Probe . . . . . . . . . . . . . . . . . . . . . . . 137
7.3 A Probe Composed of Three Mutually Perpendicular Dipoles . . . . . . . . . 140
7.4 Comments and Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 145
Chapter 8 Other Factors Limiting Measurement Accuracy. . . . . . . . . . . . 151
8.1 Thermal Stability of a Field Meter . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 151
8.2 The Dynamic Characteristics of the Detector. . . . . . . . . . . . . . . . . . . . . . . 158
8.3 Measured Field Deformations. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 164
8.4 Susceptibility of the Meter to External EMF . . . . . . . . . . . . . . . . . . . . . . . 167
8.5 Resonant Phenomena . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 172
8.6 Human Factor . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 175
8.7 Uncertainty Budget. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 177
Chapter 9 Photonic EMF Measurements. . . . . . . . . . . . . . . . . . . . . . . . . . . 183
9.1 The Photonic EMF Probe . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 186
9.2 Frequency Response of the Probe. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 190
9.3 Sensitivity of the Photonic Probe . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 194
9.4 Magnetic Field Photonic Probe. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 199
9.5 Detector Linearity. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 200
9.6 Synthesis of the Spherical Directional Pattern . . . . . . . . . . . . . . . . . . . . . . 201
9.7 The “Future Meter”. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 203
Chapter 10 Final Comments . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 207
Index . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 215
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Preface
The importance of electromagnetic field measurement is greater now
than ever before. This situation is only going to increase because of the
increase in devices emitting radiation and the subsequent need for
improved knowledge of sources in EMC. Near-field measurement is also
very important for biomedical applications where the knowledge of
fields is important for the protection of personnel. Far-field measure-
ments are generally well understood and well documented. However,
this is not the case with near-field measurements, and the sources and
causes of errors in these measurements can lead to results that indicate
only a passing resemblance to the real values.
Pawel Bienkowski and Hubert Trzaska have produced a book that
will be invaluable to those designing or using near-field measurement
probes. This book shows WHAT should measured, WHY it needs to be
measured, and HOW it should be measured. It contains detailed
designs and analysis of the circuits to be used.
Pawel Bienkowski and Hubert Trzaska are both internationally
respected researchers and practitioners. This book is based on years of
experience and builds on the previous edition. It blends absolute aca-
demic rigor with satisfying a practical need. It clearly has a place on the
bookshelves of practicing EMC engineers and test and measurement
engineers. It is also essential reading for those involved in environmen-
tal monitoring of EM fields and medical physicists who need to under-
stand EM exposure.
vii
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Trzaska.book Page ix Wednesday, September 28, 2011 4:22 PM
Preface to the Second Edition
This is a revision of Electromagnetic Field Measurements of the Near
Field, published in 2001 through Noble Publishing. Though we have
streamlined the title, the proliferation of electronic devices and their
resulting sources of electromagnetic fields (EMF) has dramatically
increased. The misunderstandings and questions concerning EMF mea-
surements, particularly in the near field, have led us to explain the phe-
nomena and measurement techniques in more detail and with greater
clarity. Also, a remarkable number of errors occur in near-field mea-
surements. Presenting an understanding of their causes and essence
should be quite valuable to those who undertake such measurements
and the interpretation of results.
A greater understanding of near-field EMF measurements and
causes of errors will be particularly beneficial to readers concerned with
these three areas:
• The design and manufacture EMF probes
• Measurements taken for labor safety and environment protection
purposes, as well as research in the area of bioelectromagnetics
• Interpretation of measurement results for legal decisions bearing
on standards, regulations, and compliance
In our investigation of meters currently available on the market, the
authors have found they do not always meet certain metrological
requirements for accuracy. Perhaps the manufacturers are indifferent
or unaware of the conditions in which their products will be applied. On
the other hand, users of the devices may not be using these meters cor-
rectly or may be unaware of how to test them to understand their limi-
tations. It is our hope that this book will assist manufacturers and
users alike to better understand the many variables that can cause
errors and to recognize them when they occur. A misunderstanding or
misinterpretation of the EMF measurement’s accuracy is especially
ix