Determining the peak spatial-average specific absorption rate (SAR) in the human body from wireless communications devices, 30 MHz to 6 GHz - Part 1: General requirements for using the finite difference time-domain (FDTD) method for SAR calculations

IEC/IEEE 62704-1:2017(E) defines the methodology for the application of the finite-difference time domain (FDTD) technique when used for determining the peak spatial-average specific absorption rate (SAR) in the human body exposed to wireless communication devices with known uncertainty. It defines methods to validate the numerical model of the device under test (DUT) and to assess its uncertainty when used in SAR simulations. Moreover, it defines procedures to determine the peak spatial-average SAR in a cubical volume and to validate the correct implementation of the FDTD simulation software. The applicable frequency range is 30 MHz to 6 GHz.
This document does not recommend specific SAR limits since these are found elsewhere, for example, in the guidelines published by the International Commission on Non-Ionizing Radiation Protection (ICNIRP) [1] or in IEEE Std C95.1 [3].
Key words: Spatial-Average Specific Absorption Rate, Finite-Difference Time-Domain, Human Body

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IEC/IEEE 62704-1:2017 - Determining the peak spatial-average specific absorption rate (SAR) in the human body from wireless communications devices, 30 MHz to 6 GHz - Part 1: General requirements for using the finite difference time-domain (FDTD) method for SAR calculations
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IEC/IEEE 62704-1
Edition 1.0 2017-10
INTERNATIONAL
STANDARD
Determining the peak spatial-average specific absorption rate (SAR) in the
human body from wireless communications devices, 30 MHz to 6 GHz –
Part 1: General requirements for using the finite-difference time-domain (FDTD)
method for SAR calculations
IEC/IEEE 62704-1:2017-10(en)
---------------------- Page: 1 ----------------------
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---------------------- Page: 2 ----------------------
IEC/IEEE 62704-1
Edition 1.0 2017-10
INTERNATIONAL
STANDARD
Determining the peak spatial-average specific absorption rate (SAR) in the
human body from wireless communications devices, 30 MHz to 6 GHz –
Part 1: General requirements for using the finite-difference time-domain (FDTD)
method for SAR calculations
INTERNATIONAL
ELECTROTECHNICAL
COMMISSION
ICS 17.220.20; 33.060.20 ISBN 978-2-8322-4769-3

Warning! Make sure that you obtained this publication from an authorized distributor.

® Registered trademark of the International Electrotechnical Commission
---------------------- Page: 3 ----------------------
– 2 – IEC/IEEE 62704-1:2017
© IEC/IEEE 2017
CONTENTS

FOREWORD ........................................................................................................................... 5

INTRODUCTION ..................................................................................................................... 7

1 Scope .............................................................................................................................. 8

2 Normative references ...................................................................................................... 8

3 Terms and definitions ...................................................................................................... 9

4 Abbreviated terms ......................................................................................................... 15

5 Finite-difference time-domain method – basic definition ................................................. 16

6 SAR calculation and averaging ...................................................................................... 17

6.1 Calculation of SAR in FDTD voxels ....................................................................... 17

6.2 SAR averaging ...................................................................................................... 18

6.2.1 General ......................................................................................................... 18

6.2.2 Calculation of the peak spatial-average SAR ................................................. 20

6.2.3 Calculation of the whole body average SAR ................................................... 24

6.2.4 Reporting peak spatial-average SAR and whole body average SAR............... 24

6.2.5 Referencing peak spatial-average SAR and whole body average SAR ........... 24

6.3 Power scaling ....................................................................................................... 25

7 SAR simulation uncertainty ............................................................................................ 26

7.1 Considerations for the uncertainty evaluation ........................................................ 26

7.2 Uncertainty of the test setup with respect to simulation parameters ...................... 27

7.2.1 General ......................................................................................................... 27

7.2.2 Positioning ..................................................................................................... 27

7.2.3 Mesh resolution ............................................................................................. 28

7.2.4 Absorbing boundary conditions ...................................................................... 29

7.2.5 Power budget ................................................................................................ 29

7.2.6 Convergence ................................................................................................. 29

7.2.7 Dielectrics of the phantom or body model ...................................................... 30

7.3 Uncertainty and validation of the developed numerical model of the DUT .............. 31

7.3.1 General ......................................................................................................... 31

7.3.2 Uncertainty of the DUT model (d ≥ λ/2 or d ≥ 200 mm) ................................... 31

7.3.3 Uncertainty of the DUT model (d < λ/2 and d < 200 mm) ................................ 33

7.3.4 Model validation ............................................................................................ 34

7.4 Uncertainty budget ................................................................................................ 35

8 Code verification............................................................................................................ 36

8.1 General ................................................................................................................. 36

8.2 Code accuracy ...................................................................................................... 37

8.2.1 Free space characteristics ............................................................................. 37

8.2.2 Planar dielectric boundaries .......................................................................... 42

8.2.3 Absorbing boundary conditions ...................................................................... 45

8.2.4 SAR averaging .............................................................................................. 48

8.3 Canonical benchmarks .......................................................................................... 50

8.3.1 Generic dipole ............................................................................................... 50

8.3.2 Microstrip terminated with ABC ...................................................................... 51

8.3.3 SAR calculation SAM phantom / generic phone ............................................. 52

8.3.4 Setup for system performance check ............................................................. 53

Annex A (normative) Fundamentals of the FDTD method ..................................................... 55

Annex B (normative) SAR Star ............................................................................................. 59

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IEC/IEEE 62704-1:2017 – 3 –
© IEC/IEEE 2017

B.1 CAD files of the SAR Star ..................................................................................... 59

B.2 Mesh lines for the SAR Star .................................................................................. 59

B.2.1 General ......................................................................................................... 59

B.2.2 Mesh lines for the homogeneous SAR Star .................................................... 59

B.2.3 Mesh lines for the inhomogeneous SAR Star ................................................. 60

B.3 Evaluation of the SAR Star benchmark ................................................................. 60

B.3.1 General ......................................................................................................... 60

B.3.2 File format of the benchmark output............................................................... 60

B.3.3 Evaluation script ............................................................................................ 61

Annex C (informative) Practical considerations for the application of FDTD ......................... 65

C.1 Overview............................................................................................................... 65

C.2 Practical considerations ........................................................................................ 66

C.2.1 Computational requirements .......................................................................... 66

C.2.2 Voxel size ...................................................................................................... 67

C.2.3 Stability ......................................................................................................... 67

C.2.4 Absorbing boundaries .................................................................................... 67

C.2.5 Far-zone transformation ................................................................................ 68

C.3 Modelling requirements for sources and loads ...................................................... 68

C.4 Calculation of S-parameters .................................................................................. 70

C.5 Calculation of power and efficiency ....................................................................... 70

C.6 Non-uniform meshes ............................................................................................. 71

Annex D (informative) Background information on tissue modelling and anatomical

models .................................................................................................................................. 73

D.1 Dielectric tissue properties .................................................................................... 73

D.2 Anatomical models of the human body .................................................................. 73

D.3 Recommended numerical models of experimental phantoms ................................. 73

D.3.1 Experimental head phantom .......................................................................... 73

D.3.2 Experimental body phantom........................................................................... 74

Bibliography .......................................................................................................................... 75

Figure 1 – Field components on voxel edges ........................................................................ 17

Figure 2 – Flow chart of the SAR averaging algorithm ........................................................... 20

Figure 3 – Illustration of valid and used voxels in a valid averaging cube centred on the

highlighted voxel and an invalid averaging volume for which a new cube has to be

expanded about the surface voxel because it contains more than 10 % of background

material ................................................................................................................................ 22

Figure 4 – Valid, used and partially used voxels ................................................................... 23

Figure 5 – “Unused” location ................................................................................................. 24

Figure 6 – Aligned parallel-plate waveguide and locations of the E -field components to

be recorded for TE-polarization ............................................................................................. 37

Figure 7 – Permissible power reflection coefficient (grey range) for the aligned

absorbing boundary conditions ............................................................................................. 46

Figure 8 – Tilted parallel-plate waveguide terminated with absorbing boundary

conditions and locations of the E -field components to be recorded for TE-polarization ....... 47

Figure 9 – Permissible power reflection coefficient (grey range) for the tilted absorbing

boundary conditions .............................................................................................................. 48

Figure 10 – Sketch of the testing geometry of the averaging algorithm .................................. 49

Figure 11 – 3D view of the SAR Star ..................................................................................... 50

Figure 12 – Geometry of the microstrip line ........................................................................... 52

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– 4 – IEC/IEEE 62704-1:2017
© IEC/IEEE 2017

Figure 13 – Geometry of the setup for the system performance check according to [31]....... 53

Figure A.1 – Voxel showing the arrangement of the E- and H-field vector components

on a staggered mesh ............................................................................................................ 57

Figure A.2 – Voxels with different dielectric properties surrounding a mesh edge with

an E -component .................................................................................................................. 58

Figure C.1 – FDTD voltage source with source resistance ................................................... 69

Figure C.2 – Four magnetic field components surrounding the electric field component

where the source is located .................................................................................................. 69

Table 1 – Voxel states during SAR averaging ....................................................................... 22

Table 2 – Factors contributing to the uncertainty of experimental and numerical SAR

evaluation ............................................................................................................................. 27

Table 3 – Budget of the uncertainty contributions of the numerical algorithm and of the

rendering of the test- or simulation-setup .............................................................................. 30

Table 4 – Budget of the uncertainty of the developed model of the DUT................................ 34

Table 5 – Numerical uncertainty budget ................................................................................ 36

Table 6 – Results of the evaluation of the numerical dispersion characteristics .................... 42

Table 7 – Results of the evaluation of the numerical reflection coefficient ............................ 44

Table 8 – Results of the dipole evaluation ............................................................................. 51

Table 9 – Results of the microstrip evaluation ....................................................................... 52

Table 10 – 1 g and 10 g psSAR for the SAM phantom exposed to the generic phone

for 1 W accepted antenna power as specified in [22]............................................................. 52

Table 11 – Dielectric parameters of the setup (Table 1 of [31]) ............................................ 54

Table 12 – Mechanical parameters of the setup (Tables 1 and 2 of [31]) .............................. 54

Table 13 – psSAR normalized to 1 W forward power and feedpoint impedance (Tables

3 and 4 of [31]) ..................................................................................................................... 54

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IEC/IEEE 62704-1:2017 – 5 –
© IEC/IEEE 2017
INTERNATIONAL ELECTROTECHNICAL COMMISSION
____________
DETERMINING THE PEAK SPATIAL-AVERAGE SPECIFIC ABSORPTION
RATE (SAR) IN THE HUMAN BODY FROM WIRELESS
COMMUNICATIONS DEVICES, 30 MHz TO 6 GHz –
Part 1: General requirements for using the finite-difference
time-domain (FDTD) method for SAR calculations
FOREWORD

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---------------------- Page: 7 ----------------------
– 6 – IEC/IEEE 62704-1:2017
© IEC/IEEE 2017

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International Standard IEEE/IEC 62704-1 has been prepared by IEC technical committee 106:

Methods for the assessment of electric, magnetic and electromagnetic fields associated with

human exposure, in cooperation with the International Committee on Electromagnetic Safety

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This publication is published as an IEC/IEEE Dual Logo standard.
This standard contains attached files in the form of CAD models and
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A list of all parts in the IEC/IEEE 62704 series, published under the general title Determining

the peak spatial-average specific absorption rate (SAR) in the human body from wireless

communications devices, 30 MHz to 6 GHz, can be found on the IEC website.

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---------------------- Page: 8 ----------------------
IEC/IEEE 62704-1:2017 – 7 –
© IEC/IEEE 2017
INTRODUCTION

Computational techniques have reached a level of maturity which allows their use in specific

absorption rate (SAR) assessment of wireless communication devices. Some wireless

communication devices are used in situations where experimental SAR assessment is

extremely complex or not possible at all. National regulatory bodies (e.g. US Federal

Communications Commission) encourage the development of consensus standards and

encouraged the establishment of the ICES Technical Committee 34 Subcommittee 2. The

benefits to the users and the regulators include standardized and accepted protocols,

anatomically correct body models, validation techniques, benchmark data, reporting format

and means for estimating the computational uncertainty in order to produce valid, accurate,

repeatable, and reproducible data.
---------------------- Page: 9 ----------------------
– 8 – IEC/IEEE 62704-1:2017
© IEC/IEEE 2017
DETERMINING THE PEAK SPATIAL-AVERAGE SPECIFIC ABSORPTION
RATE (SAR) IN THE HUMAN BODY FROM WIRELESS
COMMUNICATIONS DEVICES, 30 MHz TO 6 GHz –
Part 1: General requirements for using the finite-difference
time-domain (FDTD) method for SAR calculations
1 Scope

This part of IEC/IEEE 62704 defines the methodology for the application of the finite-

difference time domain (FDTD) technique when used for determining the peak spatial-average

specific absorption rate (SAR) in the human body exposed to wireless communication devices

with known uncertainty. It defines methods to validate the numerical model of the device

under test (DUT) and to assess its uncertainty when used in SAR simulations. Moreover, it

defines procedures to determine the peak spatial-average SAR in a cubical volume and to

validate the correct implementation of the FDTD simulation software. The applicable

frequency range is 30 MHz to 6 GHz.

NOTE Cubical averaging volumes are applied in all current experimental standards for the assessment of the

peak spatial-average SAR (psSAR) and recommended by [1], [2] and [3]. Other averaging volumes have been

proposed, for example, in [1], and may be included in future revisions of this document.

This document does not recommend specific SAR limits since these are found elsewhere, for

example, in the guidelines published by the International Commission on Non-Ionizing

Radiation Protection (ICNIRP) [1] or in IEEE Std C95.1 [3].
2 Normative references

The following documents are referred to in the text in such a way that some or all of their

content constitutes requirements of this document. For dated references, only the edition

cited applies. For undated references, the latest edition of the referenced document (including

any amendments) applies.

NOTE The experimental standards that define the SAM phantom and the testing positions are IEEE Std 1528 and

IEC 62209-1.

IEEE Std 1528, IEEE Recommended Practice for Determining the Peak Spatial-Average

Specific Absorption Rate (SAR) in the Human Head from Wireless Communications Devices:

Measurement Techniques

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 devices used next to the ear

(frequency range of 300 MHz to 6 GHz)

IEC 60050 (all parts), International Electrotechnical Vocabulary (IEV) (available at:

http://www.electropedia.org)

IEEE Standards Dictionary Online (subscription available at: http://dictionary.ieee.org)

---------------------- Page: 10 ----------------------
IEC/IEEE 62704-1:2017 – 9 –
© IEC/IEEE 2017
3 Terms and definitions

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