Mobile Antenna Systems Handbook

Mobile Antenna Systems Handbook Third Edition Kyohei Fujimoto Editor page iii Revised Master Set 05-15-08 10:12:57 Library of Congress Cataloging...
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Mobile Antenna Systems Handbook Third Edition Kyohei Fujimoto Editor

page iii

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Library of Congress Cataloging-in-Publication Data A catalog record for this book is available from the U.S. Library of Congress. British Library Cataloguing in Publication Data A catalogue record for this book is available from the British Library. ISBN-13: 978-1-59693-126-8 Cover design by Igor Valdman  2008 ARTECH HOUSE, INC. 685 Canton Street Norwood, MA 02062 All rights reserved. Printed and bound in the United States of America. No part of this book may be reproduced or utilized in any form or by any means, electronic or mechanical, including photocopying, recording, or by any information storage and retrieval system, without permission in writing from the publisher. All terms mentioned in this book that are known to be trademarks or service marks have been appropriately capitalized. Artech House cannot attest to the accuracy of this information. Use of a term in this book should not be regarded as affecting the validity of any trademark or service mark. 10 9 8 7 6 5 4 3 2 1

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Contents Preface to the Third Edition

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Chapter 1 Importance of Antennas in Mobile Systems and Recent Trends 1.1 Introduction 1.2 Trends 1.2.1 Mobile Systems 1.2.2 Increasing Information Flow 1.2.3 Propagation 1.3 Modern Mobile Antenna Design 1.4 Objectives of This Book References

1 1 9 13 15 15 15 19 22

Chapter 2 Essential Techniques in Mobile Antenna Systems Design 2.1 Mobile Communication Systems 2.1.1 Technologies in Mobile Communications 2.1.2 Frequencies Used in Mobile Systems 2.1.3 System Design and Antennas 2.2 Fundamentals in Land Mobile Propagation 2.2.1 Propagation Problems in Land Mobile Communications 2.2.2 Multipath Propagation Fundamentals 2.2.3 Classification of Multipath Propagation Models: NB, WB, and UWB 2.2.4 Spatio-Temporal Propagation Channel Model 2.2.5 Relation Between Space Correlation Characteristics and Space Diversity Effect 2.2.6 Propagation Modeling for OFDM 2.2.7 Propagation Studies for UWB References

25 25 25 31 33 34 34 36

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Chapter 3 Advances in Mobile Propagation Prediction Methods 3.1 Introduction 3.2 Macrocells 3.2.1 Definition of Parameters 3.2.2 Empirical Path Loss Models 3.2.3 Physical Models 3.2.4 Comparison of Models 3.2.5 Computerized Planning Tools 3.2.6 Conclusions 3.3 Microcells 3.3.1 Dual-Slope Empirical Models 3.3.2 Physical Models 3.3.3 Nonline-of-Sight Models 3.3.4 Microcell Propagation Models: Discussion 3.3.5 Microcell Shadowing 3.3.6 Conclusions 3.4 Picocells 3.4.1 Empirical Models of Propagation Within Buildings 3.4.2 Empirical Models of Propagation into Buildings 3.4.3 Physical Models of Indoor Propagation 3.4.4 Constitutive Parameters for Physical Models 3.4.5 Propagation in Picocells: Discussion 3.4.6 Multipath Effects 3.4.7 Conclusions 3.5 Megacells 3.5.1 Shadowing and Fast Fading 3.5.2 Local Shadowing Effects 3.5.3 Empirical Narrowband Models 3.5.4 Statistical Models 3.5.5 Physical-Statistical Models for Built-Up Areas 3.5.6 Wideband Models 3.5.7 Multisatellite Correlations 3.5.8 Overall Mobile-Satellite Channel Model 3.6 The Future 3.6.1 Intelligent Antennas 3.6.2 Multidimensional Channel Models 3.6.3 High-Resolution Data 3.6.4 Analytical Formulations 3.6.5 Physical-Statistical Channel Modeling 3.6.6 Real-Time Channel Predictions 3.6.7 Overall References

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Chapter 4 Antennas for Base Stations 4.1 Basic Techniques for Base Station Antennas 4.1.1 System Requirements 4.1.2 Types of Antennas 4.1.3 Radio Zone Design 4.1.4 Diversity 4.2 Design and Practice of Japanese Systems 4.2.1 Multiband Antennas 4.2.2 Remote Beam Tilting System 4.2.3 Antennas for Radio Blind Areas 4.2.4 Antennas for CDMA Systems 4.3 Adaptive Antenna Systems 4.3.1 Personal Handy Phone System 4.3.2 W-OAM 4.3.3 i-Burst System 4.3.4 Experimental System of Adaptive Array for WCDMA 4.3.5 Experimental System of Adaptive Array for CDMA2000 1xEV-DO 4.4 Design and Practice II (European Systems) 4.4.1 Antenna Configurations 4.4.2 Antenna Solutions 4.4.3 Antenna Units 4.4.4 Antenna Development Trends References

141 141 141 143 144 146 151 151 157 158 164 170 170 172 173 175

Chapter 5 Antennas for Mobile Terminals 5.1 Basic Techniques for Mobile Terminal Antennas 5.1.1 General 5.1.2 Brief Historical Review of Design Concept 5.1.3 Modern Antenna Technology 5.2 Design and Practice of Antennas for Handsets I 5.2.1 Some Fundamental Issues 5.2.2 Various Multiband Antenna Concepts 5.2.3 Antenna Integration and Some Practical Issues 5.2.4 The Multichannel Antenna Applications 5.2.5 Human Body Interaction with Terminal Antennas and Some Measurement Methods 5.3 Design and Practice of Antennas for Handsets 5.3.1 Multiband and Broad Band Antenna Technologies 5.3.2 Diversity Antenna Technologies 5.3.3 Antenna Technologies Mitigating Human Body Effect 5.3.4 Antenna Technologies for Reducing SAR

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5.3.5 Technique of Omitting Balun 5.3.6 Technology of Downsizing PIFA 5.4 Evaluation of Antenna Performance 5.4.1 Measurement Method Using Optical Fiber References Radio Frequency Exposure and Compliance Standards for Mobile Communication Devices 6.1 Introduction 6.2 Physical Parameters 6.3 Types of RF Safety Standards 6.4 Exposure Standards 6.4.1 ICNIRP 6.4.2 IEEE C95.1-2005 6.4.3 Similarities and Differences Between the 1998 ICNIRP Guidelines and IEEE C95.1-2005 6.4.4 Regulations Based on Older Standards 6.5 Compliance Standards 6.5.1 Main Features of IEEE 1528-2003 (Including 1528a-2005) and IEC 62209-1 6.5.2 Other Standards Related to Mobile Communication 6.6 Discussion and Conclusions References

304 307 309 309 313

Chapter 6

330 330 333 333 339 339 341

Chapter 7 7.1 7.2

7.3 7.4

7.5

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Applications of Modern EM Computational Techniques: Antennas and Humans in Personal Communications Introduction Definition of Design Parameters for Handset Antennas 7.2.1 Absorbed Power and Specific Absorption Rate 7.2.2 Directivity and Gain 7.2.3 Antenna Impedance and S 11 Finite-Difference Time-Domain Formulation Eigenfunction Expansion Method 7.4.1 EEM Implementation 7.4.2 Hybridization of the EEM and MoM Results Using EEM 7.5.1 Human Head Model 7.5.2 EM Interaction Characterizations 7.5.3 Effects of Size of the Head Model: Adult and Child 7.5.4 Comparison Between Homogeneous and Multilayered Spheres 7.5.5 Vertical Location of Antennas 7.5.6 Comparison with EEM and FDTD

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7.5.7 Anatomical Head Versus Spherical Head 7.5.8 Directional Antennas 7.5.9 High-Frequency Effect 7.6 Results Using the FDTD Method 7.6.1 Tissue Models 7.6.2 Input Impedance and the Importance of the Hand Position 7.6.3 Gain Patterns 7.6.4 Near Fields and SAR 7.7 Assessment of Dual-Antenna Handset Diversity Performance 7.7.1 Dual-Antenna Handset Geometries 7.7.2 Simulated Assessment of Diversity Performance 7.7.3 Experimental Assessment of Diversity Performance 7.7.4 Results References Chapter 8 Digital TV Antennas for Land Vehicles 8.1 Reception Systems 8.1.1 Digital Television Services in Japan 8.1.2 Problems of Mobile Reception 8.1.3 Diversity Reception Methods 8.1.4 Demonstration 8.2 Digital Television Antennas 8.2.1 Quarter Glass Antenna for a Van 8.2.2 Thin Antenna 8.2.3 Omnidirectional Pattern Synthesis Technique for a Car 8.2.4 Antennas Currently on the Market References

399 399 399 400 400 402 405 405 407 408 410 415

Chapter 9.1 9.2 9.3

417 417 418 419 419 421 425

Chapter 10 Antennas for ITS 10.1 General 10.2 Antenna Design 10.2.1 Communication Beam Coverage 10.2.2 Antenna Fundamental Design

427 427 429 429 431

9 Antennas for the Bullet Train Introduction Train Radio Communication Systems Antenna Systems 9.3.1 LCX Cable 9.3.2 Train Antenna References

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10.2.3 Microstrip Antenna Design 10.2.4 Communication Coverage 10.2.5 Multiple Reflections 10.3 Field Strength in Communication Area 10.3.1 Multiple Reflections from Canopies 10.3.2 Mitigation Using an Absorber at the ETC Gate 10.3.3 Propagation in DSRC Coverage 10.3.4 Data Rate of DSRC 10.4 Antennas for DSRC 10.5 Applications for DSRC References Chapter 11 Antennas for Mobile Satellite Systems 11.1 Introduction 11.2 System Requirements for Vehicle Antennas 11.2.1 Mechanical Characteristics 11.2.2 Electrical Characteristics 11.2.3 Propagation Problems 11.3 Omnidirectional Antennas for Mobile Satellite Communications 11.3.1 Overview 11.3.2 Quadrifilar Helical Antenna 11.3.3 Crossed-Drooping Dipole Antenna 11.3.4 Patch Antenna 11.4 Directional Antennas for Mobile Satellite Communications 11.4.1 Antennas for INMARSAT 11.4.2 Directional Antennas in the ETS-V Program 11.4.3 Airborne Phased Array Antenna in the Domestic Satellite Phone Program 11.4.4 Directional Antennas in the MSAT Program 11.4.5 Directional Antennas in the Ku-Band CBB Program 11.5 Antenna Systems for GPS 11.5.1 General Requirements for GPS Antennas 11.5.2 Quadrifilar Helical Antennas 11.5.3 Microstrip Antennas 11.6 Multiband Antennas for Future GPS/ITS Services 11.6.1 Slot Ring Multiband Antenna for Future Dual Bands (L1 , L2 ) GPS 11.6.2 Microstrip Multiband Antennas for GPS, VICS, and DSRC 11.7 Satellite Constellation Systems and Antenna Requirements 11.7.1 Constellation Systems and Demands on Antenna Design 11.7.2 Handset Antennas for Satellite Systems References

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Chapter 12 UWB Antennas 12.1 UWB Systems: Introduction 12.2 Requirements for UWB Antennas 12.2.1 Basic Principle of UWB Antennas 12.2.2 Modeling and Structure of Feeding Points 12.2.3 Current Distributions of Circular Disc Monopole Antenna 12.3 Characteristics of Popular UWB Antennas 12.3.1 Three-Dimensional UWB Antennas 12.3.2 Planar UWB Antennas 12.3.3 CPW Feed 12.3.4 Multilayer Technologies 12.3.5 Band-Rejection for Coexistence with Other Wireless Systems 12.4 Wire-Structured UWB Antennas and Wire-Grid Modeling Simulation 12.4.1 High Efficiency Moment Method 12.5 UWB Antennas in Specific Wireless Environments 12.5.1 UWB Antennas Used in Unlicensed and Autonomous Wireless Environments 12.5.2 Measurements of Multipath Propagation Environments for UWB Antennas 12.5.3 Transmission Characteristics of UWB Antennas and Effects of the Human Body 12.5.4 UWB Antennas Near the Human Body 12.6 UWB Antenna Evaluation Indexes 12.7 UWB Antenna Measurements 12.7.1 Radiation Pattern Measurements 12.7.2 Impedance Measurements 12.7.3 Scale Model Measurements 12.7.4 Impedance Measurements with Two Coaxial Cables 12.8 Integrated Antenna Design Approach Based on LSI Technology 12.9 Radio Wave Resource Sharing with Technology Leadership and the Role of the Antenna References Chapter 13 Antennas for RFID 13.1 The Characteristics of an RFID System 13.1.1 What Is RFID? 13.1.2 Operating Frequencies 13.1.3 Operating Principles 13.1.4 Read Range 13.2 Reader Antennas 13.2.1 Fixed Reader 13.2.2 Mobile Reader

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13.3

Tag Antennas 13.3.1 Structure of a Tag Antenna 13.3.2 Impedance Matching 13.3.3 Tags on Metallic Surface 13.3.4 Bandwidth-Enhanced Tag Antennas 13.3.5 SAW Tags 13.4 Measurement of Tag Antennas 13.4.1 Measurement of the Tag Antenna Impedance 13.4.2 Read Range Measurement 13.4.3 Efficiency Measurement References

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Chapter 14 Multiple-Input Multiple-Output (MIMO) Systems 14.1 Introduction 14.2 Diversity in Wireless Communications 14.2.1 Time Diversity 14.2.2 Frequency Diversity 14.2.3 Space Diversity 14.3 Multiantenna Systems 14.4 MIMO Systems 14.5 Channel Capacity of the MIMO Systems 14.6 Channel Known at the Transmitter 14.6.1 Water-Filling Algorithm 14.7 Channel Unknown at the Transmitter 14.7.1 Alamouti Scheme 14.8 Diversity-Multiplexing Trade-Off 14.9 MIMO Under an Electromagnetic Viewpoint 14.9.1 Case Study 1 14.9.2 Case Study 2 14.9.3 Case Study 3 14.9.4 Case Study 4 14.9.5 Case Study 5 14.10 Conclusions References

619 619 620 620 621 622 623 624 627 628 629 629 630 631 632 634 635 635 639 641 643 644

Chapter 15.1 15.2 15.3 15.4

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15 Smart Antennas Definition Why Smart Antennas? Introduction Background

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15.5

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Beam Forming 15.5.1 Minimum Mean Square Error 15.5.2 Minimum Variance Distortionless Response 15.6 Direct Data Domain Least Squares (D3LS) Approaches to Adaptive Processing Based on a Single Snapshot of Data 15.6.1 Eigenvalue Method 15.6.2 Forward Method 15.6.3 Backward Method 15.6.4 Forward-Backward Method 15.7 Simulations 15.8 Conclusion References

659 662 663 665 666 667 671 671

Appendix A Glossary A.1 Catalog of Antenna Types A.1.1 Linear Antennas A.1.2 Material Loading A.1.3 Planar Antenna A.1.4 Broadband and Multiband Antennas A.1.5 Balance-Unbalance Transforming A.1.6 Arrays and Diversity Systems A.1.7 Recent Innovative Concepts References A.1.8 Key to Symbols and Acronyms Used in Sections A.2 to A.3 A.2 Land Mobile Systems A.2.1 Automobiles A.2.2 Portable Equipment A.2.3 Trains A.2.4 Base Stations A.2.5 Satellite Systems A.2.6 UWB A.2.7 RFID A.3 Typical Antenna Types and Their Applications

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Acronyms and Abbreviations

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List of Contributors

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Index

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Chapter 6 Radio Frequency Exposure and Compliance Standards for Mobile Communication Devices C-K. Chou and Ron Petersen

The study of the biological effects associated with exposure to electromagnetic energy has a rich history going back almost a century. Although much of the earlier work was carried out as a matter of scientific curiosity, since the mid-1950s the majority of the research has been focused on filling gaps in the knowledge-base regarding safety in order to develop rational radio frequency (RF) safety standards and guidelines to protect against established adverse health effects in humans. Members of the public and RF workers continue to raise questions about the safety of new RF technologies, including radar, radio and television broadcasting facilities, microwave ovens, point-to-point microwave radio, and satellite communications systems. The most recent concern is the safety of mobile and portable telephones and their base stations. Consequently, much of the bioeffects research carried out during the past 15 years is specific to conditions relative to exposure to portable telephones. The results of this research are used to ensure that contemporary safety guidelines and standards adequately protect the public and the worker, or if changes are necessary. Two types of standards directly related to the safety of mobile communication devices are described in this chapter: (1) safety standards that recommend limits to protect against harmful effects associated with RF exposure, and (2) conformance (or compliance) standards that describe protocols to ensure that RF-emitting devices, such as portable telephones, comply with the safety standards. 321

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6.1 INTRODUCTION Public awareness of the dramatic increase in the number of systems that emit RF energy frequently leads to questions about safety. For example, during the past few decades, questions have arisen about the safety of radar, radio and television broadcasting facilities, microwave ovens, point-to-point microwave radio, and satellite communications systems, and most recently, mobile and portable telephones and their base stations. The range of RF power at which mobile and portable wireless communication devices operate may be as low as a few mW for a Bluetooth device; a fraction of a watt for a mobile phone; up to 7W for two-way mobile radios; several tens of watts for mobile radio systems installed in motor vehicles; and up to 100W, or more, for certain mobile telephone and two-way radio base stations. Even though they operate at lower power than base station and vehiclemounted mobile radio antennas, handheld devices have the potential for producing higher exposures, especially to important organs such as the brain and eyes, because of their proximity to the caller’s body during normal use. Although exposure from base station antennas is far less than that from handheld devices, the public appears to be more concerned about the safety of base stations. Sound, science-based safety standards help to allay the fears of those who approach the RF safety issue with an open mind. In this chapter, the relevant parameters used to assess exposure, and the types of standards that address the safety of mobile communication devices are described— specifically safety standards that recommend limits to protect against harmful effects associated with RF exposure, and conformance (or compliance) standards that describe protocols to ensure that RF-emitting devices comply with the safety standards. For purposes of this chapter, the frequency range of interest is 30 MHz to 6 GHz, which includes the frequencies most commonly used for mobile communications. 6.2 PHYSICAL PARAMETERS Radio frequencies are loosely defined as frequencies between 3 kHz and 300 GHz—that is, frequencies below the infrared region of the electromagnetic spectrum. Because the photon energy associated with an RF electromagnetic wave is far below that required to remove an electron from an atom (ionization), RF exposure is characterized as nonionizing radiation, as is infrared radiation, visible light, and the longer ultraviolet wavelengths. The physical interaction of RF energy with biological material is complex, often resulting in highly nonuniform distributions of the induced electric (E) and magnetic (H) fields and the induced current density within the object regardless of the uniformity of the external exposure fields. The internal fields are related to a dosimetric quantity, called specific absorption rate (SAR), which was first proposed by the National Council on Radiation Protection and Measurements in 1981 [1], and defined as the time derivative of the incremental energy absorbed by (dissipated in) an incremental mass contained in a volume of a given density and is expressed in W/kg. The internal electric field strength,

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induced current density, and SAR are related to the physical and electrical properties of the absorbing object by the following equations: SAR =

E=

␴ 2 E ␳

W/kg

冉 冊 ␳ SAR ␴

(6.1)

1/2

J = (␴␳ SAR )1/2

V/m

(6.2)

A/m

(6.3)

where E is the root-mean-square value of the induced electric field strength (V/m) in tissue, J is the current density (A/m2) in tissue, ␳ is the tissue density (kg/m3), and ␴ is the dielectric conductivity of the tissue (S/m). In a tutorial on RF dosimetry, Chou et al. [2] discuss the relationship between SAR and the characteristics of the incident field and the geometrical and electrical properties of the absorbing object. SAR patterns, whole-body averaged SAR, and methods for the measurement of peak SAR, are also discussed. (Details for the measurement of peak SAR for mobile phones and other portable devices are described in Section 6.5.) In order to determine the thresholds for harmful effects and develop exposure limits to protect against such effects, it is necessary to know the magnitude and distribution of the SAR within the exposed object. The SAR depends not only on the properties of the incident field, including the magnitudes of E and H (or equivalent power density); it also depends on the dielectric properties, geometry, size, and orientation of the exposed object, the polarization and frequency of the incident fields, the source configuration, exposure environment, and time-intensity factors. Figure 6.1 shows the parameters associated with human exposure to RF energy. 6.3 TYPES OF RF SAFETY STANDARDS There are three types of RF standards related to human safety. The first type is the ‘‘safety’’ standard, which sets limits to protect against harmful effects associated with RF exposure. Currently two recognized international organizations develop RF safety standards and guidelines. One, now called the Institute of Electrical and Electronics Engineers (IEEE) International Committee on Electromagnetic Safety (ICES) Technical Committee 95, has a history of RF safety standard activities that traces back to the late 1950s. The first RF safety standard was published by this committee in 1966 [4]; four revisions have been published since then—the latest in 2006 [5]. This committee develops

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Figure 6.1 External and internal physical parameters of human exposure to RF energy. (Modified from Guy [3].)

standards through an open consensus process that is transparent at every level; that is, the committee is open to anyone with an expressed material interest, the meetings are open, and meeting records are posted on the Internet. A total of 130 members representing 24 countries were involved with developing the latest revision of this standard (IEEE C95.1-2005) [5], including members of government, academia, industry and the general public. (See Petersen [6] for a detailed historical record.) In 2006, this standard was approved by the American National Standards Institute and is recognized as an American National Standard (ANSI/IEEE C95.1-2006). The second international organization that develops RF safety guidelines is the International Commission on Non-Ionizing Radiation Protection (ICNIRP), which consists of 14 elected members from various government organizations and academia (but no members representing commercial interests). The ICNIRP guidelines, developed mostly in closed forums, are endorsed and promoted globally by the World Health Organization for adoption by national governments. Most countries in the world adopt the basic restrictions or derived limits of either the ICNIRP guidelines or the IEEE standard. Similarities and differences in the recommendations from IEEE and ICNIRP are presented in Section 6.4.3. The second type of standard is the product standard which recommends methodologies for ensuring products comply with the safety standards. The committees that develop international product standards for mobile communications devices are IEEE ICES Technical Committee 34 (TC-34) and International Electrotechnical Commission (IEC) TC-106. TC-34 is a relatively new committee established in 1995 (compared with ICES TC-95,

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which was established as an American Standards Association Committee in 1960); IEC TC-106 was established in 2000. Although TC-34 and TC-95 are both ICES committees, the TC-34 product standard for mobile telephones IEEE 1528-2003 [7] is used for determining compliance with TC-95 and ICNIRP recommendations to allow manufacturers to readily ensure that their products comply with these or similar requirements. The goal is to provide unambiguous procedures that yield repeatable results (e.g., similar to the procedure for certifying compliance of microwave ovens). In addition to standards for measuring the peak SAR associated with handheld mobile telephones, TC-34 is in the process of developing product standards for vehicle-mounted antennas, as well as for other devices using both measurement and numerical techniques [8]. Recent collaboration between ICES TC-34 and IEC TC-106 led to the development of the product standard for hand-held devices IEC 62209-1 [9], which is harmonized with IEEE 1528-2003. The third type of RF safety standard protects against indirect effects associated with RF energy. Examples of this type of standard include compatibility standards (e.g., standards for limiting electromagnetic interference with electronic equipment on aircraft or in medical environments). Compatibility standards, developed by the American National Institute of Standards, International Standard Organization, Consumer Electronics Association and others, are not discussed further in this chapter. 6.4 EXPOSURE STANDARDS As early as the mid-1950s, recommendations to limit exposure to RF energy were adopted by various agencies and organizations throughout the world. The first RF exposure standard published in the United States (USAS C95.1-1966) [4] limited RF-induced heating of the body. The recommended exposure limit was 100 W/m2 averaged over any 0.1-hr interval; the applicable frequency range was 10 MHz to 100 GHz. In the mid-1970s, dosimetry studies revealed that the interaction of RF energy with biological bodies is extremely complex, and a frequency-independent limit over a broad frequency range is unrealistic. The third revision of the 1966 standard (American National Standards Institute ANSI C95.1-1982) [10] incorporated dosimetry, which resulted in frequency-dependent limits based on whole-body-averaged and peak spatial-average SAR (to address localized exposure). In 1986, the National Council on Radiation Protection and Measurements (NCRP) adopted the 1982 ANSI standard as the upper tier for occupational exposure, but added an additional safety factor of 5 for a lower tier for exposure of the public [11]. The upper tier includes a 10-fold safety factor; the lower tier has an additional factor of 5 (i.e., a total safety factor of 50 below the threshold for effects considered adverse). The IEEE Committee adopted this approach, and the revision of the 1982 C95.1 standard (IEEE C95.1-1991) [12] also contains two tiers, as does the 1998 ICNIRP guidelines [13]. Although the ICNIRP guidelines and the 1991 IEEE standard are based on limiting the whole-body-averaged SAR to the same values of 0.4 and 0.08 W/kg for the upper and lower tiers, respectively, the peak spatial-average SAR limits differ, both in magnitude

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and in averaging volume. This discrepancy caused confusion for the general public, extra burdens for manufacturers, and discordance among the regulators. During the revision process that led to IEEE C95.1-2005 [5], consideration was given to harmonizing with the ICNIRP guidelines where scientifically justifiable. An important issue that was addressed is the peak SAR limits which are now essentially identical in the new IEEE standard and ICNIRP guidelines. The 1998 ICNIRP guidelines and IEEE C95.1-2005 are detailed in the following sections. 6.4.1 ICNIRP The most recent ICNIRP guidelines, approved in November 1997, were published in 1998 [13]. As in the case of the ANSI and IEEE committees, the ICNIRP guidelines are based on studies reporting established adverse health effects. In agreement with the rationale of C95.1-1991, ICNIRP also found that the relevant established effects are surface effects at the lower frequencies (e.g., electrostimulation, shocks and burns) and effects associated with tissue heating at the higher frequencies. Although a number of in vitro studies were reviewed, the focus was on in vivo studies. Epidemiological studies of reproductive outcome and cancer were reviewed but because of the lack of adequate exposure assessment and inconsistency of results, these studies were found to be of little use for establishing science-based exposure criteria. Studies reporting athermal effects, including ‘‘window effects’’ [e.g., effects associated with ELF amplitude modulated (AM) RF fields] were also considered, but ICNIRP concluded: ‘‘Overall, the literature on athermal effects of AM electromagnetic fields is so complex, the validity of reported effects so poorly established, and the relevance of the effects to human health is so uncertain, that it is impossible to use this body of information as a basis for setting limits on human exposure to these fields’’ [13]. The more recent review of the literature by IEEE led to the following conclusions regarding low-level effects: ‘‘Despite more than 50 years of RF research, low-level biological effects have not been established. No theoretical mechanism has been established that supports the existence of any effect characterized by trivial heating other than microwave hearing. Moreover, the relevance of reported low-level effects to health remains speculative and such effects are not useful for standard setting’’ [5, p. 82]. Standard-setting organizations (e.g., ANSI, IEEE) and organizations that develop recommendations and guidelines (e.g., NCRP and ICNIRP) have all determined that SAR is the appropriate dosimetric parameter over the broad whole-body resonance region and also found that the most reliable and sensitive indicator of potential harm was behavioral disruption, with a threshold SAR of 4 W/kg. A safety factor of 10 was incorporated for exposures in the workplace, and an additional factor of 5 for exposure of the general public yielding maximum whole-body-average SAR values of 0.4 and 0.08 W/kg, respectively (called basic restrictions). In addition, basic restrictions in terms of peak spatialaverage SAR of 10 and 2 W/kg averaged over any 10-g contiguous tissue are recommended for localized exposure. The ICNIRP peak spatial-average SAR values are based on the

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thresholds of cataract formation in rabbit eyes (about 10g) with safety factors of 10 and 50. The ICNIRP limits for high-peak, low-average-power pulsed fields are based on the evoked auditory response (microwave hearing [14, 15]) whereas the corresponding C95.1-1991 and C95.1-2005 limits are based on the stun-effect in small animals (with a suitable margin of safety) [16]. That is, while ICNIRP considers ‘‘microwave hearing’’ a harmful effect, it is not considered an adverse effect in the C95.1-2005 standard [5, pp. 81–82]. Table 6.1 shows the basic restrictions (SAR) of the ICNIRP guidelines for frequencies between 100 kHz to 10 GHz, both for occupational and for general-public exposure. Table 6.2 lists the derived limits (reference levels) for the incident fields. While compliance with the reference levels ensures that the basic restrictions are met, because of the conservatism built into the reference levels, exceeding the reference levels does not mean that the Table 6.1 1998 ICNIRP Basic Restrictions

Exposure Group

Frequency

Whole Body Avg. SAR W/kg

Occupational General Population

100 kHz to 10 GHz 100 kHz to 10 GHz

0.4 0.08

Local SAR (Head and Trunk) W/kg

Local SAR (Limbs) W/kg

10 (10g) 2 (10g)

20 (10g) 4 (10g)

Source: [13]. Table 6.2 1998 ICNIRP Reference Levels Frequency

E Field (V/m)

H Field (A/m)

Power Density (W/m 2 )

Occupational 3 to 65 kHz 0.065 to 1 MHz 1 to 10 MHz 10 to 400 MHz 400 to 2,000 MHz 2 to 300 GHz

610 610 610/f 61 3f 1/2 1.37

24.4 1.6/f 1.6/f 0.16 0.008f 1/2 0.36

10 f /40 50

General Population 3 to 150 kHz 0.15 to 1 MHz 1 to 10 MHz 10 to 400 MHz 400 to 2,000 MHz 2 to 300 GHz

87 87 87/f 1/2 28 1.375f 1/2 61

5 0.73/f 0.73/f 0.073 0.0037f 1/2 0.16

2 f /200 10

Source: [13].

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basic restrictions are exceeded. For additional details of ICNIRP recommendations, refer to the ICNIRP guidelines [13].

6.4.2 IEEE C95.1-2005 IEEE C95.1-2005 was approved on October 5, 2005, and published on April 19, 2006. The purpose of this standard is to provide recommendations to protect against established adverse effects to human health associated with exposure to RF electric, magnetic, and electromagnetic fields over the frequency range of 3 kHz to 300 GHz [5]. This revision (of C95.1-1991) is based on an evaluation of the scientific literature through 2003 (although the literature cutoff date was December 2003, several papers published in 2004 and 2005 were included), including those studies that involve low-level exposures where increases in temperature could not be measured or were not expected. New insights gained from improved experimental and numerical methods and a better understanding of the effects of acute and chronic RF electromagnetic field exposures of animals and humans are included. A lack of credible scientific and medical reports showing adverse health effects for RF exposures at or below corresponding exposure limits in past standards supports the protective nature of this standard. Above 100 kHz, the limits are designed to protect against adverse health effects resulting from tissue heating, the only established mechanism relating to adverse effects of exposure to RF energy at these frequencies. For the first time, guidance on the necessity of an RF exposure control program (e.g., recommendations in IEEE C95.7-2005 [17]) is included. The C95.1 standard consists of normative sections, including an overview of the document (scope, purpose, and introduction), references, definitions, and recommendations, as well as informative sections. The informative sections include seven annexes; the first three explain the revision process, summary of the literature, and rationale of the revision; the fourth provides examples of practical applications; and the last three annexes are glossary, literature database, and bibliography. Refer to the standard [5] for details, especially on the literature summary of about 1,300 peer-reviewed papers (Annex B) and the rationale (Annex C).

6.4.2.1 Recommendations The recommendations are expressed in terms of basic restrictions (BRs) and maximum permissible exposure (MPE) values (sometimes called reference levels or investigation levels). The BRs are limits on internal fields, SAR, and current density; the MPEs, derived from the BRs, are limits on external fields and on induced and contact currents. The recommendations are intended to apply to all human exposures except for exposure of patients by, or under the direction of, physicians and medical professionals.

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Basic Restrictions The whole-body-average BRs shown in Table 6.3 for frequencies between 100 kHz and 3 GHz protect against established adverse health effects associated with heating of the body during whole-body exposure. Consistent with the approach used in the prior standards and the ICNIRP guidelines, a traditional safety factor of 10 has been applied to the established SAR threshold of 4 W/kg for such effects, yielding an SAR of 0.4 W/kg averaged over the whole body. In the absence of an RF safety program, the BRs of the lower tier (action levels) may also be used for the general public. Applied to members of the general public, the lower tier provides more assurance that continuous, long-term exposure of all individuals in the population will be without risk of adverse effects. The BRs in terms of peak spatial-average SAR shown in Table 6.3 protect against excessive temperature rise in any part of the body that might result from localized or nonuniform exposure. As the frequency increases above 3 GHz, the power deposition becomes more superficial and SAR less meaningful. To account for the shallow penetration depth at the higher frequencies, the BRs are expressed in terms of incident power density and are identical to the derived limits (MPEs). Although exposure at or near these values may be accompanied by a slight sensation of warmth, this effect is not considered adverse. Maximum Permissible Exposure Values The derived limits (MPEs) in terms of equivalent power density, considered appropriate for all human exposure, are shown in Figure 6.2. (For detailed information on averaging time, refer to Table 6.4 and [5].) 6.4.2.2 RF Safety Programs Throughout the RF spectrum, the BRs and MPEs apply to exposure of people (i.e., compliance is determined by whether exposures of people to RF fields, currents, and Table 6.3 Basic Restrictions for Frequencies Between 100 kHz and 3 GHz

Whole-body exposure Localized exposure Localized exposure

(Whole-body Average) (Local peak spatial-average) (Extremitiesb and pinnae)

Action Level SAR (W/kg)

Persons in Controlled Environments SAR (W/kg)

0.08 2a 4a

0.4 10a 20a

a

Averaged over any 10g of tissue (defined as a tissue volume in the shape of a cube). The extremities are the arms and legs distal from the elbows and knees, respectively. Source: [5].

b

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Figure 6.2 IEEE C95.1-2005 [5] MPEs for the upper and lower tiers in the frequency band 100 kHz to 300 GHz, as compared to reference levels in ICNIRP guidelines [13].

voltages exceed the applicable values). Where there may be access to RF fields, currents, and/or voltages that exceed the lower tier (action level) BRs and MPEs of IEEE C95.1-2005, an RF safety program such as detailed in IEEE Std C95.7-2005 [17] can be implemented to ensure that exposures do not exceed the MPEs or BRs for the upper tier (persons in a controlled environment). 6.4.3 Similarities and Differences Between the 1998 ICNIRP Guidelines and IEEE C95.1-2005 Table 6.4 compares various parameters of the 1998 ICNIRP guidelines with the corresponding parameters of C95.1-2005. This comparison indicates that while the two documents are similar, there are some differences between the two that suggests a need for continued harmonization efforts to achieve one global standard. 6.4.4 Regulations Based on Older Standards In the United States, the Federal Communications Commission (FCC), in 1996, adopted a combination of the IEEE C95.1-1991 and NCRP 1986 exposure criteria to regulate RF

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Table 6.4 Comparison of the 1998 ICNIRP Guidelines [13] with the IEEE C95.1-2005 Standard [5] over the Frequency Range Where the Predominant Interaction Mechanism Is Tissue Heating Parameter

ICNIRP

IEEE C95.1-2005

Frequency range Recognition of whole-body resonance Incorporation of dosimetry (SAR) Database of experimental literature Most significant biological endpoint

∼ 100 kHz to 300 GHz Yes

∼ 100 kHz to 300 GHz Yes

Yes

Yes

Large

Very large (∼ 1,300 citations)

Behavioral disruption (associated with ∼ 1°C core temperature rise) 1–4 W/kg

Behavioral disruption (associated with ∼ 1°C core temperature rise) ∼ 4 W/kg

0.4 W/kg (occupational) 0.08 W/kg (general public) 100 kHz to 10 GHz

0.4 W/kg (controlled environment) 0.08 W/kg (action level) 100 kHz to 3 GHz 10 W/kg (controlled environment) 2 W/kg (action level) 10g of tissue in the shape of a cube 6 minutes (controlled environments) 30 minutes (action level) 20 W/kg (extremities and pinnae) 4 W/kg (extremities and pinnae) 100 kHz < f ≤ 3 GHz 6 minutes ( f ≤ 3 GHz) then decreasing to 10 seconds at 300 GHz) 6 min (3 kHz ≤ f ≤ 1.34 MHz). E 2 and H 2 have different averaging times for 1.34 MHz < f ≤ 100 MHz but both are equal to 30 minutes at 100 MHz. For 100 MHz < f ≤ 5 GHz the averaging time is 30 minutes and then decreases to 10 seconds at 300 GHz. 90 mA (each foot) 45 mA (each foot) 100 kHz ≤ f ≤ 110 MHz

Whole-body-averaged SAR associated with behavioral disruption Limiting whole-body-averaged SAR —Applicable frequency range Peak spatial-average SAR (localized exposure) —Averaging volume —Averaging time

10 W/kg (occupational) 2 W/kg (general public) 10g of contiguous tissue 6 minutes (occupational) 6 minutes (general public)

Limits for extremities —Upper tier —Lower tier —Applicable frequency range Averaging time ( f > 100 kHz) —Upper tier —Lower tier

20 W/kg (limbs) 4 W/kg (limbs) 100 kHz < f ≤ 10 GHz

Induced and contact current limits —Upper tier —Lower tier —Applicable frequency range

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40 mA (limb currents) 20 mA (limb current) 100 kHz ≤ f ≤ 110 MHz

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Table 6.4 (continued) Comparison of the 1998 ICNIRP Guidelines [13] with the IEEE C95.1-2005 Standard [5] over the Frequency Range Where the Predominant Interaction Mechanism Is Tissue Heating Parameter

ICNIRP

IEEE C95.1-2005

Special criterion for modulated fields Specific limits for high-peak, low-average-power pulses

No

No

Yes. Based on evoked auditory response (‘‘microwave hearing’’) Not specifically

Yes. Based on the stun-effect

RF safety program

Yes. IEEE C95.7-2005. The BRs and MPEs of the lower tier (action level) are linked to an RF safety program to mitigate against exposures that could exceed the BRs and MPEs of the upper tier

Source: [6].

exposures from transmitting equipment (including mobile communications) [18]. The basic restrictions for the whole body exposure is the same as those of ICNIRP and IEEE C95.1-2005, but the peak SAR is 1.6 and 8 W/kg averaged over any 1g of tissue for exposure in controlled environments (occupational exposure) and general-public exposure, respectively. The MPEs are shown in Table 6.5. Table 6.5 FCC Limits for Maximum Permissible Exposure (MPE) Frequency (MHz)

E Field (V/m)

H Field (A/m)

Power Density* (W/m 2 )

Exposure in Controlled Environments (Occupational) 0.3 to 3 614 1.63 3 to 30 1842/f 4.89/f 2 30 to 300 61.4/f 0.163 300 to 1,500 — — 1500 to 100,000 — —

1000 9000/f 2 10 f /30 50

Exposure in Uncontrolled Environments (General Population) 0.3 to 1.34 614 1.63 1.34 to 30 824/f 2.19/f 30 to 300 27.5 0.073 300 to 1,500 — — 1,500 to 100,000 — —

1000 1800/f 2 f /150 10

*Plane-wave equivalent power density. Source: [19].

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At the time this chapter was prepared, the FCC had not taken an action to issue a Notice of Proposed Rule Making for public comment in order to initiate the process for revising the above limits based on the new IEEE C95.1-2005 Standard or any other RF safety recommendations.

6.5 COMPLIANCE STANDARDS Several standards are used to ensure that various products (e.g., mobile phones and base stations) comply with contemporary safety standards, guidelines, and national regulations. For whole body exposures, compliance with the MPEs (reference levels) can be determined by measuring the incident fields using commercially available survey meters, or similar devices, following the protocols described in standards such as IEEE C95.3-2002 [20]. For near field exposures from specific devices, particularly handheld and portable devices, determination of the SAR is usually required. In 1996, IEEE Standards Coordinating Committee 34 (now IEEE ICES TC-34) began drafting a standard that specifies measurement protocols for certifying that mobile phones meet peak spatial-average SAR requirements. The result of this effort is IEEE 1528-2003 [7] and 1528a-2005 [21]. The European Committee for Electrotechnical Standardization (CENELEC) published a similar standard (EN50361) in July 2001 [22]. Because of minor differences between the two standards (e.g., the values for some tissue simulant parameters for certain frequencies), some products are required to be tested twice, once for the European and Australian markets and once for other parts of the world. This duplication emphasized the need for a globally harmonized test method. This issue was resolved with the publication of IEC 62209-1 [9] which is harmonized with IEEE 1528-2003 and replaces the CENELEC standard (EN50361).

6.5.1 Main Features of IEEE 1528-2003 (Including 1528a-2005) and IEC 62209-1 IEEE ICES TC-34 Subcommittee 2 and IEC TC-106 Project Team 62209 share common membership and goals for harmonized international standards for the measurement of peak SAR for mobile phones intended for use when placed next to the head. As a result, both the IEEE standards (1528-2003 and 1528a-2005) and IEC 62209-1 are technically identical. These standards specify measurement protocols designed to allow various laboratories to perform SAR measurements in a consistent manner. Included is a standard phantom model with specified size and shape, specific liquid compounds for tissue simulation, standard calibration techniques for E-field probes, and phone positioning requirements. Some of the salient features of the two standards are described below. For details of the SAR measurement protocol, the reader should refer to the original standards: IEEE 1528-2003 [7]; IEEE 1528a-2005 [21]; and IEC 62209-1 [9].

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SAR Measurement System Figure 6.3 shows a typical SAR measurement system used to perform SAR measurement in a head phantom. The system consists of an E-field probe, dc voltage amplifiers, highimpedance cables connecting the amplifier outputs to a personal computer, a controlling robot, a simulated tissue phantom, and a holder assembly for placing the phone with respect to the phantom. The robot holding the probe scans the entire exposed volume of the phantom in order to evaluate the three-dimensional field distribution. The entire system, including the E-field probe, is calibrated in a controlled laboratory environment in each tissue equivalent liquid at the appropriate operating frequency.

Figure 6.3 Mobile phone SAR measurement system showing robot-controlled electric field probe for SAR measurement in a head phantom exposed to a mobile phone at the left ear.

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Phantom Model To simulate the human head, both committees agreed to use the dielectric property values of Gabriel et al. [23]. Table 6.6 lists the dielectric properties of the equivalent head tissue at various frequencies based on a plane-wave analysis [24]. The dielectric constant is the average of all head tissues, and the conductivity is the larger of the 1g or 10g average calculated effective conductivity. Formulas for liquid head tissue phantoms for the various frequency bands are included in the IEEE and IEC standards. The dielectric constant and conductivity are required to be within 5% of the target values at the specified frequencies, excluding instrument error, and must be checked periodically to ensure compliance. The measured dielectric properties of the liquid at the device operating frequencies should be used in SAR calculations instead of the target values shown in Table 6.6. The U.S. Army head model (90% adult male head dimensions and shape) [25] was adopted by both committees from which a hairless specific anthropomorphic mannequin (SAM) of the head was constructed. Figure 6.4 shows the side view of SAM with ear structure and marking lines. The ear protrusion of the Army head model (28 mm) was reduced to 4 mm to simulate the compression of the ear during mobile phone use. This spacing brings the phone close to the head and provides results that are relevant to the exposure of the population with smaller ears, such as children. The SAM shell is made of fiberglass with a thickness no greater than 2 mm at the site of measurement, except at the ear. The relative dielectric constant of the shell is less than 5 and the conductivity less than 0.01 S/m. A 4-mm lossless spacer plus the 2-mm shell thickness at the ear canal is used to simulate the ear. All dimensions are specified in a CAD file. Right and left head models, obtained by bisecting the fiberglass SAM shell, are necessary because the asymmetric location of the antenna in many phones results in Table 6.6 Dielectric Properties of the Equivalent Head Tissue for Frequencies Between 300 and 3,000 MHz Frequency (MHz)

Relative Dielectric Constant (⑀ r )

Conductivity (␴ ) (S/m)

300 450 835 900 1,450 1,800 1,900 1,950 2,000 2,450 3,000

45.3 43.5 41.5 41.5 40.5 40.0 40.0 40.0 40.0 39.2 38.5

0.87 0.87 0.90 0.97 1.20 1.40 1.40 1.40 1.40 1.80 2.40

Source: [7, 9].

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Figure 6.4 Side view of the SAM phantom head showing the ear and marking lines BM and NF. Intersection RE is the ear reference point (ERP). (Source: [7].)

different SAR distributions on each side of the head. The models are filled with the correct liquid mixture simulating head tissue at the desired frequency. The liquid is 15 ± 0.5 cm in depth measured at the ear canal, which is approximately equivalent to the distance between the ears of the phantom. Measurement Procedures Figure 6.5 is a flow chart of the SAR testing protocol. E-field measurements are taken at a reference point where the fields are above the noise level (e.g., 10 mm above the ear reference point) to monitor power changes during the testing. This measurement is conducted after placing the mobile phone in operation with a fully charged battery. The inside surface of the SAM phantom immediately adjacent to the phone is scanned. If the peak occurs at the border of the area, the scan is repeated using an enlarged area when possible. A volumetric scan known as a zoom scan is then conducted at the location of the peak of the area scan, and the peak spatial-average SAR is calculated. These steps are repeated if the peak spatial-average SAR touches any side of the zoom scan volume. At the end of the zoom scan, the field is measured again at the initial power measurement reference

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Figure 6.5 Flow chart of SAR testing procedures. (Source: [9].)

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point. If the power has changed by more than 5%, it is recommended that the measurements be repeated. In Step 1, the above scan evaluation is conducted at the center frequency of the device under test at two positions on each side of the head with the antenna fully extended and with it retracted (if applicable), and all operational modes (i.e., AMPS, TDMA, CDMA, and so forth). The two positions are ‘‘cheek touch’’ and ‘‘15° tilt.’’ Figure 6.6 shows the two positions. The second position (15° tilt) is achieved by positioning the phone at the cheek touch position and then pivoting the device outwards by 15° with the top of the phone against the pinna. When positioning the phones against the head, the coordinates of two types of phones are as shown in Figure 6.7. Point A on the phone is positioned against the ear reference point on the SAM phantom, and the centerline of the phone (line AB) is lined up with the back-to-mouth (BM) line on the phantom. In Step 2, the same evaluation is repeated with the phone operating at a frequency at the high end of its frequency range and again at a frequency at the low end with the phone placed at the side of the phantom and the position that resulted in the largest peak spatial-average SAR. The last step is to examine the data and determine the maximum spatial peak SAR, which is the largest value found in Steps 1 and 2. The time needed for a complete test of a new multimode phone for compliance can be up to several weeks.

Figure 6.6 ‘‘Cheek’’ and ‘‘touch’’ positions of the mobile phone on the left side of the phantom. (Source: [7].)

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Figure 6.7 Handset vertical and horizontal reference lines and reference points A, B on two example device types. (Source: [7].)

6.5.2 Other Standards Related to Mobile Communication Many contemporary communication devices now use frequencies above 3 GHz, and therefore, IEEE ICES TC-34 is developing a second amendment to IEEE 1528 to extend the frequency range from 3 to 6 GHz. TC-34 is also developing standards for assessing compliance of mobile phones and radios using numerical techniques. These include a standard specifying the general requirements for using the finite difference time domain (FDTD) method for SAR calculations, a standard specifying the specific requirements for FDTD modeling of vehicle mounted antennas, and a standard for FDTD modeling of mobile phone exposure. Through a liaison arrangement with IEEE ICES, IEC Project Team 62209 is developing Part 2 of the 62209 standard for testing two-way radios, palmtop terminals, desktop terminals, body-worn devices including accessories, as well as multiple transmitters (30 MHz to 6 GHz). Another IEC Project Team 62232 is drafting a standard for characterizing the RF electromagnetic environment near base stations used for mobile radio communication.

6.6 DISCUSSION AND CONCLUSIONS Many government agencies throughout the world have adopted regulations that ensure devices used for mobile communications are safe. Such regulations are generally based on the basic restrictions and derived limits (reference levels, MPEs) found in consensus

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standards and guidelines that protect against adverse effects associated with exposure to RF energy. The collective credible evidence on which these standards and guidelines are based has not demonstrated that exposure to RF energy at levels at or below the basic restrictions and derived limits can affect biological systems in a manner that might lead to, or augment, any health effect. Moreover, both the ICNIRP guidelines and IEEE standards are living documents—once a standard is approved, work begins on assessing the evolving database of relevant scientific literature to ensure that the limits continue to be valid (i.e., the surveillance and evaluation of the RF bioeffects literature is continuous). If any new adverse effect is established that would require a change in the current limits, the standard can be promptly revised or amended to reflect these changes. Although whole-body-averaged and peak spatial-average SAR have been the accepted dosimetric quantities for almost three decades, replacing the latter with temperature increase was discussed during development of the 2005 IEEE standard and is being explored as a possibility for the next revision. The rationale for using temperature rather than peak SAR is based on the literature showing that adverse health effects of RF exposure are associated with significant temperature increases in the body. Dosimetry studies are now in progress to identify the relationship between temperature rise and peak spatial-average SAR for future consideration. In order to ensure that such devices comply with the safety standards and guidelines, compliance standards have been developed by international committees (e.g., IEEE ICES, IEC, and CENELEC). These product/compliance standards identify specific protocols to ensure that test methods used throughout the world are consistent. One set of such standards specifies uniform SAR test methods, which are utilized by mobile phone manufacturers to demonstrate that their products comply with the requirements of the safety standards. The authors have participated in the development of both the safety (exposure) and compliance (measurement) standards. During committee deliberations that led to IEEE C95.1-2005, the focus was on conservatism; during deliberations on the compliance standards, the focus was on precision. Worst-case assumptions were always considered. While it is always a good practice to make precise and accurate measurements, there is a trade-off when assessing compliance of a device with limits having large built-in safety margins. That is, whether or not a product meets a specified limit is a compliance issue— not a safety issue. An unrealistic focus on precision causes one to lose sight of the objective (i.e., ‘‘can’t see the forest for the trees’’). The objective should be agreement on a realistic compliance method and international harmonization. Harmonized standards provide triple wins to all involved. First, consumers gain the protection of an internationally recognized safety standard and have equal access to products and services that are available to consumers elsewhere in the world. Second, regulators gain the framework for a consistent approach to regulation that is in agreement with the recommendations of the WHO, the ITU, and the WTO. Third, industry gains by developing and manufacturing products to widely accepted international standards and, once tested for compliance, can make those products available around the world in a consistent and timely manner.

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REFERENCES [1] NCRP, ‘‘Radiofrequency Electromagnetic Fields—Properties, Quantities and Units, Biophysical Interaction, and Measurements,’’ NCRP Report No. 67, National Council on Radiation Protection and Measurements, Bethesda, MD, 1981. [2] Chou, C. K., et al., ‘‘Radio Frequency Electromagnetic Exposure: A Tutorial Review on Experimental Dosimetry,’’ Bioelectromagnetics, Vol. 17, 1996, pp. 195–208. [3] Guy, A. W., ‘‘Dosimetry Associated with Exposure to Non-Ionizing Radiation: Very Low Frequency to Microwaves,’’ Health Phys., Vol. 53, 1987, pp. 569–584. [4] USAS C95.1-1966, Safety Level of Electromagnetic Radiation with Respect to Personnel, United States of America Standards Institute. [5] IEEE C95.1-2005, ‘‘IEEE Standard for Safety Levels with Respect to Human Exposure to Radio Frequency Electromagnetic Fields, 3 kHz to 300 GHz.’’ [6] Petersen, R. C., ‘‘Radiofrequency/Microwave Safety Standards,’’ in RF Dosimetry Handbook, P. Chadwick, (project leader), 2007, Chapter 6, available at http://www.emfdosimetry.org/petersen/Radiofrequency_ Safety_Standards.html. [7] IEEE 1528-2003, ‘‘IEEE Recommended Practice for Determining the Peak Spatial-Average Specific Absorption Rate (SAR) in the Human Head from Wireless Communications Devices: Measurement Techniques.’’ [8] Osepchuk, J. M., and R. C. Petersen, ‘‘Safety and Environmental Issues,’’ in The RF and Microwave Handbook, M. Golio, (ed.), Boca Raton, FL: CRC Press LLC, 2007. [9] IEC 62209-1, ‘‘Human Exposure to Radio Frequency Fields from Hand-Held and Body-Mounted Wireless Communication Devices—Human Models, Instrumentation, and Procedures—Part 1: Procedure to Determine the Specific Absorption Rate (SAR) for Hand-Held Devices used in Close Proximity to the Ear (Frequency Range of 300 MHz to 3 GHz),’’ International Electrotechnical Commission, Geneva, 2005. [10] ANSI C95.1-1982, ‘‘American National Standard Safety Levels with Respect to Human Exposure to Radio Frequency Electromagnetic Fields, 300 kHz to 100 GHz.’’ [11] NCRP, ‘‘Biological Effects and Exposure Criteria for Radiofrequency Electromagnetic Fields,’’ Report 86, National Council on Radiation Protection and Measurements, Bethesda, MD, 1986. [12] IEEE C95.1-1991, ‘‘IEEE Standard for Safety Levels with Respect to Human Exposure to Radio Frequency Electromagnetic Fields, 3 kHz to 300 GHz.’’ [13] ICNIRP (International Commission on Non-Ionizing Radiation Protection), ‘‘Guidelines for Limiting Exposure to Time-Varying Electric, Magnetic, and Electromagnetic Fields (Up to 300 GHz),’’ Health Physics, Vol. 74, 1998, pp. 494–522. [14] Chou, C. K., A. W. Guy, and R. Galambos, ‘‘Auditory Perception of Radio-Frequency Electromagnetic Fields (80th Review and Tutorial Paper),’’ J. of Acoustic Society of America, Vol. 71, No. 6, 1982, pp. 1321–1334. [15] Elder, J. A., and C. K. Chou, ‘‘Auditory Response to Pulsed Radiofrequency Energy,’’ Bioelectromagnetics, Vol. 24, Supplement 6, 2003, pp. S162–S173. [16] Guy, A. W., and C. K. Chou, ‘‘Effects of High-Intensity Microwave Pulse Exposure on Rat Brain,’’ Rad. Sci., Vol. 17, No. 5S, 1982, pp. 169S–178S. [17] IEEE C95.7-2005, ‘‘Recommended Practice for Radio Frequency Safety Programs.’’ [18] Federal Communication Commission, 47 CFR Parts 1, 2, 15, 24 and 97, ‘‘Guidelines for Evaluating the Environmental Effects of Radiofrequency Radiation,’’ August 6, 1996. [19] Federal Communications Commission, Office of Engineering and Technology, OET Bulletin 65, Edition 97-01, Washington, D.C., August 1997. [20] IEEE C95.3-2002, ‘‘Recommended Practice for Measurements and Computations of Radio Frequency Electromagnetic Fields with Respect to Human Exposure to Such Fields, 100 kHz–300 GHz.’’

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[21] IEEE 1528a-2005, ‘‘IEEE Recommended Practice for Determining the Peak Spatial-Average Specific Absorption Rate (SAR) in the Human Head from Wireless Communications Devices: Measurement Techniques—Amendment 1: CAD File for Human Head Model (SAM Phantom).’’ [22] EN50361-2001, ‘‘Basic Standard for the Measurement of Specific Absorption Rate Related to Human Exposure to Electromagnetic Fields from Mobile Phones (300 MHz–3 GHz),’’ European Committee for Electrotechnical Standardisation, (CENELEC), Brussels. [23] Gabriel, S., R. W. Lau, and C. Gabriel, ‘‘The Dielectric Properties of Biological Tissues: 2. Measurement in the Frequency Range 10 Hz to 20 GHz,’’ Phys. Med. Biol., Vol. 41, No. 11, 1996, pp. 2251–2269. [24] Drossos, A., V. Santomaa, and N. Kuster, ‘‘The Dependence of Electromagnetic Energy Absorption Upon Human Head Tissue Composition in the Frequency Range of 300–3000 MHz,’’ IEEE Trans. on Microwave Theory and Techniques, Vol. 48, No. 11, 2000, pp. 1988–1995. [25] Gordon, C. C., et al., ‘‘1988 Anthropometric Survey of U.S. Army Personnel: Methods and Summary Statistics,’’ Technical Report NATICK/TR-89/044, U.S. Army Natick Research, Development and Engineering Center, Natick, MA, September 1989.

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