SIST EN 61566:1999

SLOVENSKI STANDARD
SIST EN 61566:1999
01-januar-1999
Measurement of exposure to radio-frequency electromagnetic fields - Field
strength in the frequency range 100 kHz to 1 GHz (IEC 61566:1997)
Measurement of exposure to radio-frequency electromagnetic fields - Field strength in
the frequency range 100 kHz to 1 GHz
Messung der Belastung durch hochfrequente elektromagnetische Felder - Feldstärke im
Frequenzbereich 100 kHz bis 1 GHz
Mesure de l'exposition aux champs électromagnétiques à radiofréquence - Intensité du
champ dans la gamme de fréquences entre 100 kHz et 1 GHz
Ta slovenski standard je istoveten z: EN 61566:1997
ICS:
17.220.20 0HUMHQMHHOHNWULþQLKLQ Measurement of electrical
PDJQHWQLKYHOLþLQ and magnetic quantities
SIST EN 61566:1999 en
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

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NORME
CEI
INTERNATIONALE
IEC
61566
INTERNATIONAL
Première édition
STANDARD
First edition
1997-06
Mesure de l'exposition aux champs
électromagnétiques à radiofréquence –
Intensité du champ dans la gamme
de fréquences entre 100 kHz et 1 GHz
Measurement of exposure to radio-
frequency electromagnetic fields –
Field strength in the frequency range
100 kHz to 1 GHz
 IEC 1997 Droits de reproduction réservés  Copyright - all rights reserved
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61566 © IEC:1997 – 3 –
CONTENTS
Page
FOREWORD . 5
INTRODUCTION . 7
Clause
1 Scope. 9
2 Normative reference . 9
3 Definitions . 9
4 General technical requirements . 13
4.1 General considerations. 13
4.2 Measurements in exposure space. 15
4.3 Electromagnetic field strength. 15
4.4 Interference patterns . 15
4.5 Radiation leakage. 17
4.6 Reactive near-field . 17
4.7 Radiating near-field . 17
4.8 Summary of measurement problems. 19
4.9 Safety precautions. 19
5 Measuring instrument requirements . 19
5.1 General . 19
5.2 Electrical performance requirements. 21
5.3 Miscellaneous requirements . 23
5.4 Physical characteristics . 23
5.5 Instrument types. 23
5.6 Diode instruments . 25
5.7 Bolometric type. 27
5.8 Thermocouple type. 27
5.9 Spurious responses. 27
5.10 Calibration of instruments . 31
6 Measurement . 31
6.1 Preliminary procedures. 31
6.2 Measurement procedures . 41
Tables 1 to 4 .37
Figure 1 – Basic components of an electromagnetic field instrument . 45
Annexes
A Summary of the main restrictions given in the INIRC guidelines of 1988
that are relevant to the frequency range covered by this International Standard . 47
B Bibliography. 51

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61566 © IEC:1997 – 5 –
INTERNATIONAL ELECTROTECHNICAL COMMISSION
_________
MEASUREMENT OF EXPOSURE TO RADIOFREQUENCY
ELECTROMAGNETIC FIELDS –
Field strength in the frequency range
100 kHz to 1 GHz
FOREWORD
1) The IEC (International Electrotechnical Commission) is a worldwide organization for standardization comprising
all national electrotechnical committees (IEC National Committees). The object of the IEC is to promote
international co-operation on all questions concerning standardization in the electrical and electronic fields. To
this end and in addition to other activities, the IEC publishes International Standards. Their preparation is
entrusted to technical committees; any IEC National Committee interested in the subject dealt with may
participate in this preparatory work. International, governmental and non-governmental organizations liaising
with the IEC also participate in this preparation. The IEC collaborates closely with the International Organization
for Standardization (ISO) in accordance with conditions determined by agreement between the two
organizations.
2) The formal decisions or agreements of the IEC on technical matters express, as nearly as possible, an
international consensus of opinion on the relevant subjects since each technical committee has representation
from all interested National Committees.
3) The documents produced have the form of recommendations for international use and are published in the form
of standards, technical reports or guides and they are accepted by the National Committees in that sense.
4) In order to promote international unification, IEC National Committees undertake to apply IEC International
Standards transparently to the maximum extent possible in their national and regional standards. Any
divergence between the IEC Standard and the corresponding national or regional standard shall be clearly
indicated in the latter.
5) The IEC provides no marking procedure to indicate its approval and cannot be rendered responsible for any
equipment declared to be in conformity with one of its standards.
6) Attention is drawn to the possibility that some of the elements of this International Standard may be the subject
of patent rights. The IEC shall not be held responsible for identifying any or all such patent rights.
International Standard IEC 61566 has been prepared by subcommittee 12C: Transmitting
equipment, of IEC technical committee 12: Radiocommunications.
The text of this standard is based on the following documents:
FDIS Report on voting
103/1/FDIS 103/4/RVD
Full information on the voting for the approval of this standard can be found in the report on
voting indicated in the above table.
Annexes A and B are given for information only.

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61566 © IEC:1997 – 7 –
INTRODUCTION
Recent publications by national and international authorities responsible for developing safety
limits on exposure to radiofrequency electromagnetic fields show a consensus towards making
specific energy absorption rate (SAR) and induced current in the human body the basic limits.
Since instruments are not yet available to measure SAR directly, and because SAR and
circulating current will vary from person to person, depending on their height and weight, recent
standards specify derived secondary levels for field strength, and/or equivalent plane-wave
power flux density, for worst case conditions of electrical coupling and body size and weight.
However, in some situations, where a wide spatial variation of field strength is present, for
example, when climbing an antenna tower or mast, it may be more appropriate to measure the
contact current through the hands or feet.
Measurements of contact current are not covered by this International Standard.

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61566 © IEC:1997 – 9 –
MEASUREMENT OF EXPOSURE TO RADIOFREQUENCY
ELECTROMAGNETIC FIELDS –
Field strength in the frequency range
100 kHz to 1 GHz
1 Scope
This International Standard applies to measurements of electromagnetic fields from operational
transmitting equipment to ensure that the transmissions do not constitute a potential hazard to
workers or to the general public.
The purpose of this standard is to promote a common understanding of technical requirements
and precautions necessary for the accurate measurement of electromagnetic fields carried out
in conjunction with relevant national exposure regulations.
This standard covers transmissions in the frequency range 100 kHz to 1 GHz.
NOTE – Possible extension of this frequency range up to 2 GHz or 3 GHz will be investigated.
This International Standard does not specify limiting values for exposure as these are usually
given in exposure standards issued by responsible health authorities. This standard is,
therefore, intended to be used in conjunction with the relevant national standards or regulations
applicable in the country concerned. In the absence of any national rules restricting exposure
to radiofrequency electromagnetic fields, the recommendations of the International Non-
Ionizing Radiation Committee (INIRC) may be followed. The 1988 INIRC recommendations on
exposure limits are summarized in annex A.
2 Normative reference
The following normative document contains provisions which, through reference in this text,
constitute provisions of this International Standard. At the time of publication, the edition
indicated was valid. All normative documents are subject to revision, and parties to agreements
based on this International Standard are encouraged to investigate the possibility of applying
the most recent edition of the normative document indicated below. Members of IEC and ISO
maintain registers of currently valid International Standards.
IEC 60215: 1987, Safety requirements for radio transmitting equipment
3 Definitions
For the purpose of this International Standard, the following definitions apply.
3.1 dipole, elementary: Dipole of short length compared to wavelength. A mathematical
concept, widely used in theoretical antenna analysis, based on a short element of wire
compared to the wavelength carrying an oscillatory current.
3.2 exposure: Occurs where a person is subjected to electric, magnetic, or electromagnetic
fields or to contact currents other than those originating from physiological processes in the
body and other natural phenomena.

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61566 © IEC:1997 – 11 –
3.3 exposure, partial – body: Occurs where RF fields are substantially non-uniform over the
body. Fields which are non-uniform over volumes comparable to the human body may occur
due to highly directional sources, standing waves, re-radiating sources, RF hot-spots, or in the
near-field.
3.4 exposure standard: Regulations, recommendations or a standard dealing with limits of
permissible exposure, published by a responsible authority.
3.5 far-field region: That region of the field of an antenna where the angular field distribution
is essentially independent of the distance from the antenna. In this region, the field has
predominately a plane-wave character, i.e. with locally uniform distributions of electric field
strength and of magnetic field strength in planes transverse to the direction of propagation.
NOTES
1 If the antenna has a maximum overall dimension D which is large compared to the wavelength, the far-field
2
region is commonly taken to exist at distances greater than 2D /λ from the antenna, λ being the wavelength.
This is the Rayleigh distance corresponding to a path difference of λ/16.
2 The far-field region is sometimes referred to as the Fraunhofer region.
3.6 near-field region: That region generally in proximity to an antenna, or other radiating
structure, where the angular field distribution is dependent upon the distance from the antenna.
In this region, the electric and magnetic fields do not have a plane-wave character. The
near-field region is further subdivided into the reactive near-field region, which is closest to the
radiating structure and which contains most or nearly all of the stored energy, and the radiating
near-field region where the radiation field predominates over the reactive field but lacks
substantial plane-wave character and is complicated in structure.
NOTES
1 For most antennas, the outer boundary of the reactive near-field region is commonly taken to exist at a
distance of one-half wavelength from the antenna surface.
2 The radiating near-field region is sometimes referred to as the Fresnel region.
3.7 non-ionizing radiation: Any electromagnetic radiation incapable of dissociating electrons
from atoms or molecules to produce ions or ionized molecules directly or indirectly. RF waves
are non-ionizing radiations.
3.8 polarization (radiated wave): That property of a radiated electromagnetic wave
describing the time varying direction and amplitude of the electric field vector; specifically the
figure traced as a function of time by the extremity of the vector at a fixed location in space, as
observed along the direction of propagation.
NOTE – In general, this figure is elliptical, traced in a clockwise or counterclockwise sense. The commonly
referenced circular and linear polarizations are obtained when the ellipse becomes a circle or a straight line,
respectively. For an observer looking in the direction of propagation, clockwise sense rotation of the electric
vector is designated right-hand polarization and counterclockwise sense rotation is designated left-hand
polarization.
3.9 power flux density: In radio wave propagation, the power crossing unit area
2
perpendicular to the direction of propagation (unit: W/m ).
For plane waves, power flux density S, r.m.s. electric field strength E and r.m.s. magnetic field
strength are related by the impedance of free-space, i.e. 377 Ω.
H
2 2
S = E /377 = 377 H

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61566 © IEC:1997 – 13 –
3.10 equivalent plane-wave power flux density: A commonly used term associated with any
electromagnetic wave, equal in magnitude to the power flux density of a plane wave having the
same electric E or magnetic H field strength.
NOTE – In the near-field and in the far-field with standing waves caused by reflective environment, the
calculations of equivalent power flux density derived from E or H are often very different from the true power
density.
3.11 re-radiated field: An electromagnetic field resulting from currents induced in a
secondary predominantly conducting object by electromagnetic waves incident on that object
from one or more primary radiating structures or antennas. (Re-radiated fields are sometimes
called "reflected" or more correctly "scattered" fields.)
3.12 response time: Time required for a field-measuring instrument to reach 90 % of the true
value after being placed in the field to be measured.
3.13 specific absorption rate (SAR): SAR is the power absorbed per kilogram of body
weight (W/kg). For whole body exposure, SAR is averaged over the whole body, but SAR may
also be averaged over specified localized areas of the body, e.g. the head or limbs. Basic limits
for exposure are usually expressed in terms of SAR and refer to a body-present situation.
Inevitably, this means the electromagnetic field distribution in the vicinity will be affected by the
presence of the body. Derived field strength values, however, refer to a body-absent situation
in which the electromagnetic field distribution is not influenced by the presence of a body.
4 General technical requirements
4.1 General considerations
The electromagnetic field radiated from an antenna is made up of a number of electric and
magnetic fields, all of which diminish with distance, d, from the source. The radiation field has
electric and magnetic components that diminish with distance as 1/d. Analysis, based upon the
concept of an elementary dipole, shows that the reactive fields comprise electric and magnetic
2
induction components which diminish as 1/
d , and a quasi-static electric field that diminishes
3
as 1/d . As a consequence of the rapid attenuation of the reactive fields, they are only of
significance very close to the antenna.
In free space far-field exposure, the energy absorbed by a person exhibits a resonant peak
when the body height approximates to 0,4 λ. For an ungrounded man of average height and
weight, this peak occurs around 70 MHz and the absorption is maximum when the body is
aligned to be parallel with the E-field vector. In this condition the absorption is about seven
times greater than for frequencies above 2 GHz. If the man is standing in good contact with
ground, the peak absorption occurs at a lower frequency, approximately 35 MHz.
The derived worst case field-strength/power flux density levels in exposure standards shall
allow for a wide variation in the height of people, from small children to tall adults. In
consequence, reduced limits usually apply over a broad band of frequencies, e.g. 10 MHz –
400 MHz.

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61566 © IEC:1997 – 15 –
Below these frequencies, there is an increasing possibility of induced currents causing
localized heating in the smaller cross-sectional areas of the body limbs, e.g. in ankles and
wrists, and also an increased risk of radiofrequency burns from touching inadequately
grounded metal objects. Different considerations therefore apply in setting the limits for electric
and for magnetic field strength below some 10 MHz – 30 MHz. As frequency is reduced, the
magnetic field-strength limit can be relaxed progressively in accordance with SAR
considerations. However, the corresponding reduction in electric field strength is
proportionately less because of the need to restrict induced currents in the limbs. Furthermore,
at frequencies below a few megahertz, a fixed upper limit may be specified to protect against
burns.
4.2 Measurements in exposure space
Unless otherwise specified, exposure field strength shall be defined as the whole space which
is possible to be occupied by a person, but measured without a human body. When it is difficult
to distinguish the occupied space clearly, e.g. when applying the regulation to general public, a
representative space of the practical situation should be selected for the measurement.
When the field strength is non-uniform over the area of concern, the measurement may be
carried out inside a unit space assumed to be occupied by the human body.
4.3 Electromagnetic field strength
In the case of a single incident electromagnetic wave, the exposure field strength, E, is given
by the square root of the sum of the squares of each field component measured on three
orthogonal axes,
2 2 2 1/2
E = (E + E + E )
x y z
In the case of multiple waves, the composite strength, E , is given by the square root of the
c
sum of the squares of the exposure field strengths of each incident wave,
2 2 1/2
E = (E + E +.)
c 1 2
4.4 Interference patterns
The reflection features of both natural and man-made structures result in non-uniform field
intensities over any region of interest due to the establishment of standing waves or other
interference patterns. This spatial variation of the electromagnetic field is caused by the
interaction of the flow of RF energy from multiple sources of energy reflected from prominent
features of the physical environment. These peaks in the electromagnetic distribution are
separated by at least one-half wavelength, i.e. they may be from a fraction of a metre to many
metres apart, depending on the frequency of the source and angles of arrival of the interfering
waves. A change in frequency can result in large changes in energy distribution.
The region of concern may be illuminated from different directions by multiple sources with
different characteristics and will encompass structures causing standing waves or coupling of
fields. These complex conditions lead to complex field configurations with hot spots at different
locations for different frequencies. Although a particular point in space may be in the far-field
or the radiating near-field of one piece of equipment, it may also be in the reactive near-fields
of some other equipment.

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61566 © IEC:1997 – 17 –
Even when the polarization characteristics of all sources are known, it is possible for certain
types of structures (such as gratings or angled supports) to modify the polarization and hence
the interference pattern in the region under investigation.
Furthermore, even when the physical environment is otherwise static, perturbations in the RF
field can be caused by the introduction of test equipment or personnel to monitor its strength,
or both. To ensure that safety requirements are met, it is imperative that any measurement
programme take account of the possibility of these and other variations. It should therefore
include a sufficiently large sampling of data desirably extending at least 0,5 λ horizontally and
vertically in order to determine the extent of any standing wave fields present. At the lower
frequencies this is, of course, impractical but the difficulty only emphasizes the desirability of
measuring both electric and magnetic fields, where this is feasible. It is likely that if one field
component is near the minima of a standing wave pattern, the other will be relatively higher.
4.5 Radiation leakage
Radiation leakage from electronic equipment presents special problems, because the source of
energy may not be clearly defined. It could be emitted from a crack in the shielding cabinet or
from poorly by-passed connecting cables. The polarization of the electromagnetic field and the
location of the leak is not generally known. This is a special case of the general near-field
situation, and the same problems can exist for all near-field measurements, whether the
emitted fields are intentional or accidental.
4.6 Reactive near-field
In the region immediately surrounding the radiation source, reactive components of the field
predominate over far-field components. Although the extent of the reactive region varies for
different types of antennas, the outer boundary of the reactive near-field is commonly taken as
λ/2 from the antenna surface. The reactive effects become increasingly predominant the closer
the source.
Although the reactive field components do not contribute to the radiation of energy, they can
couple into material and thus achieve energy absorption. Consequently, it is important that the
reactive field be measured in many situations. This can be a particularly difficult problem if
measurements are required very close to a radiation source (or a source of re-radiation by
reflection). Merely introducing a probe into a complex high-impedance field can cause serious
perturbations, and some survey instruments are not appropriate for measurements in
high-impedance fields.
4.7 Radiating near-field
In the near-field, three orthogonal components of the electric field with arbitrary relative phases
and amplitudes exist. Similarly, there are three orthogonal components of the magnetic field
with arbitrary phases and amplitudes. The electric field is elliptically polarized in an arbitrary
plane and the magnetic field, in general, is elliptically polarized in another plane.
Consequently, in the near-field, measurements of the phase and amplitude of each of the three
components of the electric field give no information about the magnetic field at the point. Thus,
use of instruments capable of measuring either the electric or the magnetic field and which
respond to any arbitrary polarization is indicated. Field measurement devices utilizing three
orthogonal dipoles or loops which detect the amplitude but not the phase of the electric or
magnetic field cannot provide complete information about the elliptically polarized field.

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61566 © IEC:1997 – 19 –
Specifically, the maximum instantaneous field vector is not measured with these types of
device. Only an averaged total field strength is measured, with the averaging occurring over
one cycle of the oscillation of the field (the carrier frequency).
Only the equivalent plane-wave power flux density corresponding to either the electric or the
magnetic field strength can be deduced. Although this term is not appropriate for near-fields,
some instruments are scaled in terms of equivalent plane-wave power flux density.
4.8 Summary of measurement problems
The electromagnetic environment is determined by many factors. Some of these are:
a) the direction of energy propagation from the sources;
b) the direction, distance and relative orientation of the source(s) and prominent features of
the physical environment with respect to the field point;
c) the field polarization, frequency, type of modulation and power of the source(s). In
general, throughout the frequency range of 100 kHz – 1 GHz covered by this standard, many
of the measurements will need to be made in near-fields and/or in reflective environments in
which standing waves are present. In most cases, it is therefore essential that
instrumentation is available for independent measurements of both the electric and
magnetic fields for all frequencies.
In fields of multiple frequency sources, frequency selective measurements should be taken,
if practicable, as the exposure limits vary with frequency.
4.9 Safety precautions
4.9.1 Warning
Survey personnel should take appropriate safety precautions while conducting measurement
surveys, and the degree of care exercized should increase in proportion to the power levels
associated with the systems being checked.
The procedures and guidance given in IEC 60215 on safety precautions for personnel working
on radio transmitting equipment should be observed where appropriate.
4.9.2 Leakage survey precautions
When performing a leakage survey, the source should first be switched off and a thorough
visual inspection of all transmission guides and cables carried out. This inspection should
determine any signs of fatigue, ageing, damage at joints or lack of adequate support.
NOTE – High fields remote from apparent sources have been traced to ladders and their surrounding guards,
which can act as waveguides.
5 Measuring instrument requirements
5.1 General
The instrument shall be supplied with a comprehensive handbook which includes a clear
statement of its performance, including any restrictions in its application, e.g. for
measurements in reactive near-fields or when multiple transmissions are present.

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61566 © IEC:1997 – 21 –
Instrumentation can be divided into three basic parts: sensor, leads and metering
instrumentation as shown in figure 1. The sensor consists of an antenna in combination with a
detector. The design and characteristics of the sensor determine to the greatest extent the
performance and application of the unit, which shall be clearly stated in the instrument
handbook. The leads refer to that part of the probe which is used to carry the responsive signal
to the metering instrumentation. To accomplish this without causing perturbation of the field,
the leads may take the form of high-resistance wires, or they may be conductive, shielded and
oriented in such a manner, that they will not couple to the field. They may also take the form of
an optical fibre link that has the particular advantage of allowing a large distance between the
sensor and the position of the operator attending the measurement. Metering instrumentation
generally takes the form of signal-conducting circuitry and display devices.
In some instrument
...