Table Of Content

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. Trzaska.book Page i Wednesday, September 28, 2011 4:22 PM E LECTROMAGNETIC M EASUREMENTS IN THE N F EAR IELD Trzaska.book Page ii Wednesday, September 28, 2011 4:22 PM 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 compatibility 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 publication 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 Trzaska.book Page iii Wednesday, September 28, 2011 4:22 PM E LECTROMAGNETIC M EASUREMENTS IN THE N F EAR IELD Pawel Bienkowski Hubert Trzaska Second Edition Trzaska.book Page iv Wednesday, September 28, 2011 4:22 PM Published by SciTech Publishing, Inc. 911 Paverstone Drive, Suite B Raleigh, NC 27615 (919) 847-2434, fax (919) 847-2568 scitechpublishing.com Copyright © 2012 by SciTech Publishing, Raleigh, NC. All rights reserved. No part of this publication may be reproduced, stored in a retrieval system or transmitted in any form or by any means, electronic, mechanical, photocopying, recording, scanning or other- wise, except as permitted under Sections 107 or 108 of the 1976 United Stated Copyright Act, without either the prior written permission of the Publisher, or authorization through payment of the appropriate per-copy fee to the Copyright Clearance Center, 222 Rosewood Drive, Dan- vers, MA 01923, (978) 750-8400, fax (978) 646-8600, or on the web at copyright.com. Requests to the Publisher for permission should be addressed to the Publisher, SciTech Publishing, Inc., 911 Paverstone Drive, Suite B, Raleigh, NC 27615, (919) 847-2434, fax (919) 847-2568, or email edi- [email protected]. The publisher and the author make no representations or warranties with respect to the accuracy or completeness of the contents of this work and specifically disclaim all warranties, including without limitation warranties of fitness for a particular purpose. Editor: Dudley R. Kay Production Manager: Robert Lawless Typesetting: J. K. Eckert & Company, Inc. Cover Design: Brent Beckley Printer: IBT Global This book is available at special quantity discounts to use as premiums and sales promotions, or for use in corporate training programs. For more information and quotes, please contact the publisher. Printed in the United States of America 10 9 8 7 6 5 4 3 2 1 ISBN: 9781891121067 Library of Congress Cataloging-in-Publication Data Cataloging in Publication Data Applied For Trzaska.book Page v Wednesday, September 28, 2011 4:22 PM 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 Trzaska.book Page vi Wednesday, September 28, 2011 4:22 PM 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 Trzaska.book Page vii Wednesday, September 28, 2011 4:22 PM 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 measurements 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 environmental monitoring of EM fields and medical physicists who need to understand EM exposure. vii Trzaska.book Page viii Wednesday, September 28, 2011 4:22 PM 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 measurements, particularly in the near field, have led us to explain the phenomena and measurement techniques in more detail and with greater clarity. Also, a remarkable number of errors occur in near-field measurements. 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