IEC/IEEE 62704-1:2026

IEC/IEEE 62704-1 ®
Edition 2.0 2026-10
INTERNATIONAL
STANDARD
Determining the peak spatial-average specific absorption rate (SAR) in the
human body from wireless communications devices, 100 kHz to 10 GHz -
Part 1: General requirements for using the finite-difference time-domain (FDTD)
method for SAR calculations
ICS 17.220.20; 33.060.20  ISBN 978-2-8327-1144-6

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CONTENTS
FOREWORD . 4
INTRODUCTION . 6
1 Scope . 7
2 Normative references . 7
3 Terms and definitions . 7
4 Abbreviated terms. 12
5 Finite-difference time-domain method . 12
5.1 Definition . 12
5.2 Requirements on the implementation of the FDTD method . 13
6 SAR calculation and averaging. 13
6.1 General . 13
6.2 Calculation of SAR in FDTD voxels . 14
6.3 Calculation of the psSAR . 16
6.3.1 Aligned psSAR calculation . 16
6.3.2 Homogeneous psSAR calculation . 21
6.3.3 Consideration of different tissue types in one averaging volume . 24
6.4 Calculation of the whole-body average SAR . 25
6.5 Power scaling . 25
6.6 Reporting peak spatial-average SAR and whole-body average SAR . 26
6.7 Referencing psSAR and whole-body average SAR . 26
7 SAR simulation uncertainty . 27
7.1 Considerations for the uncertainty evaluation . 27
7.2 Uncertainty of the test setup with respect to simulation parameters . 28
7.2.1 General. 28
7.2.2 Positioning . 29
7.2.3 Mesh resolution . 30
7.2.4 Open boundary conditions . 31
7.2.5 Power budget . 32
7.2.6 Convergence . 32
7.2.7 Dielectrics of the phantom or body model . 33
7.3 Uncertainty and validation of the developed computational model of the DUT . 33
7.3.1 General. 33
7.3.2 Uncertainty of the DUT model (d ≥ λ/2 or d ≥ 200 mm) . 34
7.3.3 Uncertainty of the DUT model (d < λ/2 and d < 200 mm) . 35
7.3.4 Model validation. 36
7.4 Uncertainty budget. 38
8 Code verification . 38
8.1 General . 38
8.2 Code accuracy . 40
8.2.1 Free space characteristics . 40
8.2.2 Planar dielectric boundaries . 46
8.2.3 Open boundary conditions . 48
8.2.4 SAR averaging . 52
8.3 Canonical benchmarks . 55
8.3.1 Generic dipole . 55
8.3.2 Microstrip terminated with open boundary conditions . 56
8.3.3 SAR calculation for SAM phantom and generic phone . 57
8.3.4 Setup for system performance check . 58
Annex A (normative) Fundamentals of the FDTD method . 59
Annex B (normative) SAR Star . 63
B.1 CAD files of the SAR Star . 63
B.2 Mesh lines for the SAR Star . 63
B.3 Evaluation of the SAR Star benchmark . 63
B.3.1 General. 63
B.3.2 File format of the benchmark output for aligned SAR averaging . 63
B.3.3 File format of the benchmark output for homogeneous SAR averaging . 64
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 . 68
C.2.4 Open boundary conditions . 68
C.2.5 Far-zone transformation . 68
C.3 Modelling requirements for sources and loads . 69
C.4 Calculation of S-parameters . 70
C.5 Calculation of power and efficiency. 71
C.6 Inhomogeneous meshes . 74
C.7 Background on development of SAR evaluation computational modelling
standards in IEC and IEEE technical committees . 74
Annex D (informative) Background information on tissue modelling and anatomical
models . 75
D.1 Dielectric tissue properties . 75
D.2 Anatomical models of the human body . 75
D.3 Recommended computational models of measurement phantoms . 75
D.3.1 Measurement head phantom . 75
D.3.2 Measurement body phantom . 76
Annex E (normative) Supplemental files and their checksums . 77
Bibliography . 78

Figure 1 – Field components on mesh cell edges . 15
Figure 2 – Flow chart of the SAR averaging algorithm . 18
Figure 3 – Illustration of valid and used voxels in a valid averaging cube centred on the
highlighted voxel and an invalid averaging volume . 19
Figure 4 – Valid, used and partially used voxels . 20
Figure 5 – "Unused" location . 21
Figure 6 – Construction of the surface sampling points and inner sampling points . 24
Figure 7 – Aligned parallel-plate waveguide and locations of the E -field components to
y
be recorded for TE-polarization . 39
Figure 8 – Permissible power reflection coefficient (grey range) for the aligned open
boundary conditions. 49
Figure 9 – Tilted parallel-plate waveguide terminated with open boundary conditions
and locations of the E -field components to be recorded for TE-polarization . 51
y
Figure 10 – Permissible power reflection coefficient (grey range) for the tilted open
boundary conditions. 52
Figure 11 – Sketch of the testing geometry of the averaging algorithm . 53
Figure 12 – 3D view of the SAR Star . 53
Figure 13 – Geometry of the microstrip line . 57
Figure 14 – Geometry of the setup for the system performance check . 57
Figure A.1 – Voxel showing the arrangement of the electric-field and magnetic-field
vector components on a staggered mesh . 61
Figure A.2 – Voxels with different dielectric properties surrounding a mesh edge with
an E -component . 62
y
Figure C.1 – FDTD voltage source with source resistance . 70
Figure C.2 – Four magnetic field components surrounding the electric field component
where the source is located . 70
Figure C.3 – Power reference planes . 73

Table 1 – Voxel states during SAR averaging . 17
Table 2 – Factors contributing to the uncertainty of measurement and computational
SAR evaluations . 28
Table 3 – Budget of the uncertainty contributions of the computational algorithm and of
the rendering of the test- or simulation-setup . 29
Table 4 – Budget of the uncertainty of the developed model of the DUT . 37
Table 5 – Computational uncertainty budget . 38
Table 6 – Results of the evaluation of the numerical dispersion characteristics . 45
Table 7 – Results of the evaluation of the numerical reflection coefficient . 48
Table 8 – Parameters for the incident electric field of Formula (30) . 55
Table 9 – Results of the dipole evaluation . 56
Table 10 – Results of the microstrip evaluation . 56
Table 11 – 1 g and 10 g psSAR for the SAM phantom exposed to the generic phone for
1 W accepted antenna power as specified in [8] . 57
Table 12 – Dielectric properties of the tissue simulant and of the phantom shell
specified in IEC/IEEE 62209-1528:2020 and [31] . 58
Table 13 – Mechanical parameters of the setup [31]. 58
Table 14 – psSAR normalized to 1 W forward power and feedpoint impedance [31] . 58

Determining the peak spatial-average specific absorption rate (SAR)
in the human body from wireless communications devices,
100 kHz to 10 GHz -
Part 1: General requirements for using the finite-difference
time-domain (FDTD) method for SAR calculations

FOREWORD
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IEC/IEEE 62704-1 was 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 of the IEEE Standards
Association, under the IEC/IEEE Dual Logo Agreement between IEC and IEEE. It is an
International Standard.
This document is published as an IEC/IEEE Dual Logo standard.
This second edition cancels and replaces the first edition published in 2017. This edition
constitutes a technical revision.
This edition includes the following significant technical changes with respect to the previous
edition:
a) specification of a SAR averaging algorithm for the calculation of the psSAR from
computational results for arbitrarily shaped homogeneous phantoms, which avoids
inconsistencies with respect to the algorithm for SAR averaging algorithm specified in
IEC/IEEE 62209-1528 for SAR measurement methods;
b) provision of SHA-256 checksums for all supplemental files;
c) addition of brief informative discussion on developmental stages of IEC and IEEE
computational modelling standards for SAR evaluations.
This standard contains attached files in the form of CAD models and reference results described
in Annex B and Annex D. Download links and checksums for these files can be found in
Annex E.
The text of this International Standard is based on the following IEC documents:
Draft Report on voting
106/722/FDIS 106/733/RVD
Full information on the voting for its approval can be found in the report on voting indicated in
the above table.
The language used for the development of this International Standard is English.
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available at www.iec.ch/members_experts/refdocs. The main document types developed by IEC
are described in greater detail at www.iec.ch/publications/.
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, 100 kHz to 10 GHz, can be found on the IEC website.
Future documents in this series will carry the new general title as cited above. Titles of existing
documents in this series will be updated at the time of the next edition.
The IEC Technical Committee and IEEE Technical Committee have decided that the contents
of this document will remain unchanged until the stability date indicated on the IEC website
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will be
– reconfirmed,
– withdrawn, or
– revised.
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 SAR measurement is extremely complex
or not possible at all. The benefits of consensus standards to users and regulators include
standardized and accepted protocols, anatomically correct body models, verification and
validation techniques, benchmark data, reporting format and means for estimating the
computational uncertainty in order to produce valid, accurate, repeatable, and reproducible
data.
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 (psSAR) in the human body exposed to wireless communication devices with
known uncertainty. It defines methods to validate the computational model of the device under
test (DUT) and to assess its uncertainty when used in SAR simulations. Moreover, it defines
procedures to determine the psSAR in a cubical volume and to verify the correct implementation
of the FDTD simulation software. The applicable frequency range is 100 kHz to 10 GHz.
This document does not recommend specific SAR limits; 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 [2].
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.
IEC/IEEE 62209-1528:2020, Measurement procedure for the assessment of specific absorption
rate of human exposure to radio frequency fields from hand-held and body-mounted wireless
communication devices - Human models, instrumentation, and procedures (Frequency range of
4 MHz to 10 GHz)
3 Terms and definitions
For the purposes of this document, the following terms and definitions apply.
IEC, ISO and IEEE maintain terminological databases for use in standardization at the following
addresses:
– IEC Electropedia: available at https://www.electropedia.org/
– ISO Online browsing platform: available at https://www.iso.org/obp
– IEEE Dictionary Online: available at https://dictionary.ieee.org
3.1
source
one or more edges of the mesh to which an associated signal feeds electric or magnetic energy
Note 1 to entry: The amplitude of the signal is proportional to an arbitrary function of time.
3.2
feed-point
part of the radiating structure where the radio-frequency currents start to support
the electromagnetic fields that carry energy away from the antenna
Note 1 to entry: Often the feed-point of the antenna is not accessible because of mechanical support requirements;
in this case a connection point is available to inject radio-frequency energy into the antenna. Normally, the connection
point is a simple connector or a waveguide flange. If not collocated, the connection and the feed-point of an antenna
are interconnected by one or more sections of transmission line. By measuring the antenna impedance at the
connection point, if the electrical characteristics of the transmission lines between the connection and the feed-point
are known, it is possible to calculate the antenna feed-point impedance.
___________
Numbers in square brackets refer to the bibliography.
3.3
antenna feed-point impedance
terminal or driving-point impedance
ratio of complex voltage to complex current at the terminals of a transmitting antenna, or the
ratio of the open-circuit voltage to the short-circuit current at the terminals of a receiving
antenna
3.4
background material
material or tissue which is not considered for the averaging volume
Note 1 to entry: Most typically, a background material will be any lossless material, such as the free-space or air
surrounding the anatomical model. It also includes air enclosures or other lumina inside the body and tissues that
have been excluded from averaging, for example, by user selection.
3.5
benchmark
simulation test specifically defined to verify simulation results based on comparison with a
reference
3.6
body
geometrical distribution of the dielectric properties and the mass densities of all live body
tissues including body fluids
Note 1 to entry: The contents of body lumina or foreign matter, such as medical implants or jewellery, are not
considered as part of the body.
3.7
conductivity
σ
ratio of the magnitude of the conduction-current density in a medium to the electric field strength
Note 1 to entry: Conductivity is expressed in units of siemens per metre (S/m).
3.8
conservative exposure
estimate of the peak spatial-average SAR and whole-body average SAR as defined in this
document that is representative of what is expected to occur in the body of a significant majority
of the population during normal operating conditions of wireless communication devices
[SOURCE: IEC/IEEE 62209-1528:2020, modified – In the definition, whole-body average SAR
has been added and explicit mention of uncertainties has been deleted.]
3.9
coverage factor
k
factor that is used to obtain the expanded uncertainty from the combined uncertainty with a
known probability of containing the true value of the measurand
3.10
far-field
region of the field of an antenna where the angular field distribution is essentially independent
of the distance from the antenna
Note 1 to entry: In this region, the field has predominantly plane wave characteristics, i.e. the electric field strength
and magnetic field strength distributions are locally uniform in planes transverse to the direction of propagation.
Note 2 to entry: For larger antennas especially, the far-field is also referred to as the Fraunhofer region.
3.11
mesh
discrete representation of the simulation model as a set of voxels in a regular three-dimensional
Cartesian arrangement
Note 1 to entry: In the scientific literature, the mesh is often referred to as "grid".
3.12
near-field
region in the field of an antenna, located near the antenna, in which the electric and magnetic
fields do not have substantial plane-wave characteristics, but vary considerably from point to
point
Note 1 to entry: The term near-field is often vaguely defined and has different meanings for large and small
antennas. The near-field is further subdivided into the reactive near-field, which is closest to the antenna and contains
most or nearly all of the stored energy associated with the field of the antenna, and the radiating near-field. If the
antenna has a maximum overall dimension that is not large compared to the wavelength, the radiating near-field
possibly does not exist. For antennas large in terms of wavelength, the radiating near-field is sometimes referred to
as the Fresnel region.
Note 2 to entry: For most antennas, the outer boundary of the reactive near-field is commonly taken to exist at a
distance of λ/2π from the antenna surface.
3.13
perfect electric conductor
PEC
material with infinite electrical conductivity which does not dissipate any energy
3.14
relative permittivity
ε
r
ratio of the complex permittivity to the permittivity of free space
Note 1 to entry: The complex relative permittivity, ε = ε /ε , of an isotropic, linear, lossy dielectric medium is from
r 0
Formula (1)
 ε ′′ 
σ
r
′ ′′ ′ ′  ′
ε = ε − jε = ε − j = ε 1− j = ε (1− j tanδ ) (1)
r r r r r r
 
ωε ε ′
0 r
 
where
−12
ε is the free space permittivity (8,854 × 10 F/m);
′
ε is the relative permittivity or dielectric constant;
r
σ is the conductivity in siemens per metre (S/m);
tanδ is the loss tangent.
jωt
Note 2 to entry: For the purposes of this document, the convention e is used to describe time-varying electric
fields.
3.15
permeability
µ
ratio of the magnetic flux density to the magnetic field strength at a point
Note 1 to entry: The permeability is expressed in units of henry per metre (H/m).
3.16
reactive field
electric and magnetic fields surrounding an antenna or other electromagnetic devices that result
in storage rather than propagation of electromagnetic energy
3.17
root-mean-square
RMS
positive square root of the mean value of the square of the function
taken over a given period
Note 1 to entry: For a periodic function y of t, the positive square root of y is from Formula (2):

(2)
Y = y (t) dt
RMS ∫

T
where
Y is the RMS value of y;
RMS
t is any value of time;
T is the period.
3.18
root-sum-square
RSS
positive square root of the sum of the squares of the elements of a set of numbers
3.19
scattering
process that causes waves incident on discontinuities or boundaries of media to be changed in
direction, phase, or polarization
3.20
specific absorption rate
SAR
time derivative (rate) of the incremental energy (dW) absorbed by (dissipated in) an incremental
mass (dm) contained in a volume element (dV) of a given density (ρ)
d dW d  dW 
 
SAR =  
  =
 
dt dm dt ρ dV
 
 
Note 1 to entry: SAR is expressed in units of watts per kilogram (W/kg) or equivalently milliwatts per gram (mW/g).
Note 2 to entry: SAR can be related to the electric field at a point by
σ | E |
SAR =
2ρ
where
σ is the conductivity of the tissue in siemens per metre (S/m);
ρ is the mass density of the tissue in kilograms per cubic metre (kg/m );
E is the peak electric field vector in volts per metre (V/m).
Note 3 to entry: SAR can be related to the increase in temperature at a point by
c∆T
SAR ≈
∆t
t=0
where
∆T is the change in temperature in degree Celsius (°C);
∆t is the duration of exposure in seconds (s);
c is the specific heat capacity in joules per kilogram and degree Celsius (J/kg °C).
This assumes that measurements are made under "ideal" circumstances, i.e. no heat loss by thermal diffusion, heat
radiation, or thermoregulation (blood flow, sweating, etc.). Moreover, this expression is valid only in the initial, linear
regime of the temperature-time curve. If this linear regime does not exist, the provided expression is not used.
3.20.1
peak spatial-average specific absorption rate
psSAR
maximum average SAR within a local region based on a specific averaging volume or mass
Note 1 to entry: SAR is expressed in watts per kilogram (W/kg) or equivalently milliwatts per gram (mW/g).
Note 2 to entry: The specific averaging volume or mass can be, for example, any 1 g or 10 g of tissue in the shape
of a cube.
Note 3 to entry: For the purpose of this document, when the averaging mass is not specified the peak spatial-
average SAR refers to both 1 g and 10 g quantities. In several tables in this document, the peak spatial-average SAR
for 1 g and 10 g is simply denoted as 1 g and 10 g SAR.
3.20.2
spatial-average specific absorption rate
sSAR
ratio of the total power dissipated in the averaging volume to the target mass of tissue within
that volume
Note 1 to entry: SAR is expressed in watts per kilogram (W/kg) or equivalently milliwatts per gram (mW/g).
Note 2 to entry: The specific averaging volume or mass can be, for example, any 1 g or 10 g of tissue in the shape
of a cube.
3.20.3
whole-body average specific absorption rate
quantity calculated as the power dissipated in the entire body divided by its mass
Note 1 to entry: SAR is expressed in watts per kilogram (W/kg) or equivalently milliwatts per gram (mW/g).
3.21
update coefficient
numerical value assigned to the voxel edges and faces calculated from the dielectric and
magnetic properties of the voxels that surround it
Note 1 to entry: The update coefficient is used to advance the numerical values of the electric and magnetic fields
in the mesh in time based on their present and past values.
3.22
voxel
volume element of the geometry to be discretized in the mesh
Note 1 to entry: In FDTD simulations for SAR calculation, the voxel is assigned the permittivity, permeability, the
electric and magnetic conductivities and the mass density of the geometry. The electric-field components of the mesh
are located in a tangential direction on the centres of the voxel edges, and the magnetic-field components of the
mesh are located in a normal direction on the centres of the voxel faces. Each edge and face is assigned an update
coefficient.
4 Abbreviated terms
ASCII American Standard Code for Information Interchange
CFL Courant–Friedrichs–Lewy
CT computed tomography
DFT discrete Fourier transformation
DUT device under test
FDTD finite-difference time-domain
FFT fast Fourier transformation
FIT finite integration technique
MIMO multiple input multiple output
MRI magnetic resonance imaging
PEC perfect electric conductor
PMC perfect magnetic conductor
PML perfectly matched layers
psSAR peak spatial-average specific absorption rate
RMS root mean square
RSS root sum square
SAM specific anthropomorphic mannequin
SAR specific absorption rate
sSAR spatial-average specific absorption rate
5 Finite-difference time-domain method
5.1 Definition
This document applies the finite-difference time-domain (FDTD) method to calculate SAR.
FDTD is extensively used for bio-electromagnetic calculations, dating back to 1975 for the
analysis of microwave heating of a human eye (Taflove and Brodwin [3]). Initially, the user shall
determine the applicability of this document by determining whether the specific computational
solution of Maxwell’s equations under consideration qualifies as an implementation of FDTD.
This is not entirely straightforward since there have been many variations of the FDTD method
developed over the time since Kane Yee’s original paper in 1966 [4], which may be taken as
defining the fundamental FDTD method. Since then, the method has received significant
attention in the scientific community. Numerous articles on the method and its extensions and
applications have been published. Several textbooks on the FDTD method recapitulate its
fundamentals, its further developments and its use ([5], [6]). Details on the application of the
FDTD method are given in Annex C.
For the application of this document, the implementation of FDTD in the region where SAR is
being calculated shall include the following characteristics.
– The electric field components are located on the edges of a Cartesian mesh composed of
rectangular parallelepipeds.
– The magnetic field components are located on the edges of a Cartesian mesh composed of
rectangular parallelepipeds which is offset from the electric field mesh by a half-voxel in
each direction.
– The computational method is a finite-difference approximation of the Maxwell curl equations
using central differences which are (at least globally) second-order accurate and may
therefore include non-uniform meshes, which are also second-order accurate (Monk and
Süli [7]).
– The computational method solves for both electric and magnetic fields by a fully explicit
leapfrog time-stepping process.
– Gauss’s laws are implicitly enforced, the fields are divergence-free, and charge is
conserved.
– The time-stepping algorithm is non-dissipative. Thus, there is no spurious decay of energy
due to non-physical artefacts of the algorithm, and artificial dissipation is not required for
stability.
NOTE Complex numerical dispersion in non-uniform meshes leads to spurious rise or decay of field amplitudes [7].
For the applications of the scope of this document, these effects are generally negligible. The impact of the numerical
dispersion is assessed within the uncertainty evaluation (Clause 7).
5.2 Requirements on the implementation of the FDTD method
The basic requirements on the FDTD method are given in Annex A. For compliance with this
document, the FDTD method shall be implemented according to these requirements. The
method shall be implemented in Cartesian coordinates in three spatial dimensions. Moreover,
SAR calculation and averaging shall be implemented according to Clause 6. The
implementation of the FDTD method shall be verified according to Clause 8.
Other methods or extensions, or both, of FDTD that satisfy the above definitions but provide
additional features may be applied provided that these features have been fully verified
according to the procedures in this document; code verification and benchmarks, etc. These
alternative methods shall provide at least the same accuracy as the FDTD method defined
above. The finite integration technique (FIT) in time domain can be regarded as an extension
of FDTD in this context.
6 SAR calculation and averaging
6.1 General
Present RF exposure standards and guidelines specify time averaged whole-body average SAR
limits and psSAR limits, neither of which shall be exceeded. The psSAR is usually averaged
over a specified mass of tissue in a cubical volume, such as the trunk, the head, an extremity
(e.g. limbs) or the pinnae. Averaging masses are specified in [1], [2] or other applicable
guidelines.
The measurement standard that defines the SAM phantom and the testing positions is
IEC/IEEE 62209-1528. The frequency range of IEC/IEEE 62209-1528 is from 4 MHz to 10 GHz,
whereas the lower end of the frequency range of this document is 100 kHz. The assumptions
on which the SAM phantom and the testing positions are based and which are outlined in
IEC/IEEE 62209-1528 apply for SAR assessment regardless of the frequency limit. As the
FDTD method does not have any intrinsic frequency limitations, the SAM phantom and the
testing positions of IEC/IEEE 62209-1528 can be applied over the entire frequency range of
this document.
Most computational studies involving the calculation of the psSAR in anatomical models of the
human body with complex tissue distribution apply Cartesian meshes and align the cubical
averaging volume with the mesh axes [8]. SAR measurement methods using homogeneous
body phant
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