SIST EN 50475:2008

SLOVENSKI STANDARD
SIST EN 50475:2008
01-september-2008
2VQRYQLVWDQGDUG]DL]UDþXQDYDQMHLQPHUMHQMHL]SRVWDYOMHQRVWLOMXGL
HOHNWURPDJQHWQLPVHYDQMHPUDGLMVNLKRGGDMQLNRYYREPRþMX+)0+]0+]
Basic standard for the calculation and the measurement of human exposure to
electromagnetic fields from broadcasting service transmitters in the HF bands (3 MHz -
30 MHz)
Grundnorm für die Berechnung und Messung der Exposition von Personen gegenüber
elektromagnetischen Feldern von Rundfunksendern in den KW-Bändern (3 MHz bis 30
MHz)
Norme de base pour le calcul et la mesure de l'exposition humaine aux champs
électromagnétiques des émetteurs de service de radiodiffusion dans les bandes HF (3
MHz a 30 MHz)
Ta slovenski standard je istoveten z: EN 50475:2008
ICS:
13.280 Varstvo pred sevanjem Radiation protection
SIST EN 50475:2008 en,fr,de
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

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SIST EN 50475:2008

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SIST EN 50475:2008

EUROPEAN STANDARD
EN 50475

NORME EUROPÉENNE
June 2008
EUROPÄISCHE NORM

ICS 13.280


English version


Basic standard for the calculation and the measurement
of human exposure to electromagnetic fields
from broadcasting service transmitters in the HF bands (3 MHz - 30 MHz)



Norme de base pour le calcul et la mesure Grundnorm für die Berechnung und
de l'exposition humaine Messung der Exposition von Personen
aux champs électromagnétiques gegenüber elektromagnetischen Feldern
des émetteurs de service de radiodiffusion von Rundfunksendern in den KW-Bändern
dans les bandes HF (3 MHz à 30 MHz) (3 MHz bis 30 MHz)





This European Standard was approved by CENELEC on 2008-04-01. CENELEC members are bound to comply
with the CEN/CENELEC Internal Regulations which stipulate the conditions for giving this European Standard
the status of a national standard without any alteration.

Up-to-date lists and bibliographical references concerning such national standards may be obtained on
application to the Central Secretariat or to any CENELEC member.

This European Standard exists in three official versions (English, French, German). A version in any other
language made by translation under the responsibility of a CENELEC member into its own language and notified
to the Central Secretariat has the same status as the official versions.

CENELEC members are the national electrotechnical committees of Austria, Belgium, Bulgaria, Cyprus, the
Czech Republic, Denmark, Estonia, Finland, France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia,
Lithuania, Luxembourg, Malta, the Netherlands, Norway, Poland, Portugal, Romania, Slovakia, Slovenia, Spain,
Sweden, Switzerland and the United Kingdom.

CENELEC
European Committee for Electrotechnical Standardization
Comité Européen de Normalisation Electrotechnique
Europäisches Komitee für Elektrotechnische Normung

Central Secretariat: rue de Stassart 35, B - 1050 Brussels


© 2008 CENELEC - All rights of exploitation in any form and by any means reserved worldwide for CENELEC members.
Ref. No. EN 50475:2008 E

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SIST EN 50475:2008
EN 50475:2008 – 2 –
Foreword
This European Standard was prepared by the Technical Committee CENELEC TC 106X,
Electromagnetic fields in the human environment.
The text of the draft was submitted to the formal vote and was approved by CENELEC as EN 50475
on 2008-04-01.
The following dates were fixed:
– latest date by which the EN has to be implemented
at national level by publication of an identical
national standard or by endorsement (dop) 2009-04-01
– latest date by which the national standards conflicting
with the EN have to be withdrawn (dow) 2011-04-01

______________

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Contents
1 Scope . 5
2 Normative references. 5
3 Terms and definitions . 5
4 Physical quantities and units . 7
5 Applicability of compliance assessment methods . 8
5.1 Reference level or action level values . 8
5.2 SAR and current density . 8
6 SAR measurement and calculation (local and average SAR) . 9
6.1 Approximate method for SAR calculation for frequencies below body resonance . 9
6.2 Exposure situation . 9
6.3 Polynomial expansion of “static” component values with frequency .10
7 Current density (3 MHz – 10 MHz) .11
8 Measurement of electric and magnetic field .12
9 Calculation of electric and magnetic field .12
10 Contact currents measurement and calculation .12
10.1 Generalities .12
10.2 Constraints .12
10.3 Equipment .13
10.4 Equivalent body impedance .13
11 Induced current calculation and measurement (10 MHz – 30 MHz) .14
11.1 Induced current calculation .14
11.2 Relation between induced current and local SAR .14
11.3 Induced current measurement .14
Annex A (informative) Data for absorption by the Visible Human body model .15
Annex B (informative) Compliance boundary examples .19
Bibliography .21

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EN 50475:2008 – 4 –
Figures
Figure 1 – Contact current measurement . 13
Figure 2 – Equivalent body impedance . 13
Figure A.1 – Calculated whole-body SAR values for the displayed polarisation for the
inhomogeneous Visible Human body model on conducting ground using
currently-accepted values for relative permittivity and conductivity at each
frequency . 15
Figure A.2 – Corresponding polarised E- and H-component parts of the whole-body SAR . 15
Figure A.3 – Model of the antenna considered . 17
Figure A.4 – Plot of the SAR calculated on the basis of the model of Visible Human on the
basis of calculated field strengths of the electric and magnetic field in front of the
studied short wave curtain antenna . 18
Figure B.1 – Model of the antenna considered . 19
Figure B.2 – Plot of the E-field strength calculated on NEC-2 basis in front of a short wave
curtain antenna . 20
Figure B.3 – Plot of the H-field strength calculated on NEC-2 basis in front of a short wave
curtain antenna . 20
Tables
Table 1 – Assessment methods for each antenna region .8
Table 2 – Assessment methods for each antenna region .8
Table A.1 – Whole-body specific absorption rate for the inhomogeneous Visible Human body
model on conducting ground for the different plane-wave polarisation orientations . 16
Table A.2 – “Static” components of the whole-body specific absorption rate for the
inhomogeneous Visible Human body model on conducting ground for the different
plane-wave polarisation orientations. 16
Table A.3 – Polynomial expansion coefficients with respect to frequency for the static
components of the whole-body specific absorption rate for the inhomogeneous
Visible Human body model on conducting ground . 17

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1 Scope
This standard applies to short wave broadcast transmitters and installations operating in the frequency
range 3 MHz to 30 MHz.
The objective of the standard is to specify, for such a frequency band, basic information allowing the
definition of a method for assessment of compliance related to human exposure to radio frequency
electromagnetic fields.
2 Normative references
The following referenced documents are indispensable for the application 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.
EN 50413, Basic standard on measurement and calculation procedures for human exposure to
electric, magnetic and electromagnetic fields (0 Hz – 300 GHz)
EN 55016 series, Specification for radio disturbance and immunity measuring apparatus and methods
(CISPR 16 series)
ENV 13005:1999, Guide to the expression of uncertainty in measurement
3 Terms and definitions
For the purposes of this document, the following terms and definitions apply.
3.1
action values
the magnitude of directly measurable parameters, provided in terms of electric field strength (E),
magnetic field strength (H), magnetic flux density (B) and power density (S), at which one or more of
the specified measures in 2004/40/EC [2] must be undertaken. Compliance with these values will
ensure compliance with the relevant exposure limit values of 2004/40/EC [2]
3.2
antenna
device that serves as a transducer between a guided wave (e.g. coaxial cable) and a free space wave,
or vice versa
3.3
basic restriction
restrictions on exposure to time-varying electric, magnetic, and electromagnetic fields that are based
directly on established health effects as given in 1999/519/EC [1]
3.4
broadcasting service
radio communication service in which the transmissions are intended for direct reception by the
general public. This service may include sound transmissions, television transmissions or other types
of transmission
3.5
compliance distance
minimum distance from the antenna to a point of investigation where field level is deemed to be
compliant to the limits

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3.6
compliance boundary
surface around the antenna outside of which all field levels are deemed to be compliant to the limits
3.7
contact current (IC)
contact current between a person and an object exposed to the field, is expressed in amperes (A).
A conductive object in an electric field can be charged by the field
3.8
current density (J)
current density is defined as the current flowing through a unit cross section perpendicular to its
direction in a volume conductor such as the human body or part of it, expressed in amperes per
square meter (A/m²)
3.9
electric field strength (E)
magnitude of a field vector at a point that represents the force (F) on a positive small charge (q)
divided by the charge
F
E =
q
Electric field strength is expressed in units of volt per meter (V/m)
3.10
exposure limit values
limits on exposure to electromagnetic fields as given in 2004/40/EC [2] which are based directly on
established health effects and biological considerations. Compliance with these limits will ensure that
workers exposed to electromagnetic fields are protected against all known adverse health effects
3.11
induced current
current induced inside the body as a result of direct exposure to electromagnetic fields, expressed in
the unit ampere (A)
3.12
installation
a particular combination of several types of apparatus and, where applicable, other devices, which are
assembled, installed and intended to be used permanently at a predefined location. In this standard,
installation includes at least one short wave transmitter
3.13
magnetic field strength (H)
vector quantity obtained at a given point by subtracting the magnetization M from the magnetic flux
density B divided by the permeability of free space µ
0

B
H=− M
µ
0
Magnetic field strength is expressed in the unit ampere per metre (A/m)
NOTE In vacuum, the magnetic field strength is at all points equal to the magnetic flux density divided by the permeability of
free space: H = B / µ0
3.14
modulation
process by which a quantity that characterises an oscillation or wave is constrained to follow the
values of a characteristic quantity of a signal
NOTE Two modulations, in particular, are used for this standard: AM (Amplitude Modulation) and COFDM (Coded Orthogonal
Frequency Division Multiplex); it must also be taken into consideration when carrying out measurements and calculations to
determine whether or not the limits are being exceeded by adding the modulation factor to the carrier r.m.s. value.

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3.15
reference levels
reference levels of exposure are provided by 1999/519/EC [1] for comparison with measured values of
physical quantities; compliance with all reference levels will ensure compliance with basic restrictions.
If measured values are higher than reference levels, it does not necessarily follow that the basic
restrictions have been exceeded, but a more detailed analysis is necessary to assess compliance with
the basic restrictions
3.16
root-mean-square (r.m.s.)
r.m.s. value is obtained by taking the square root of the average of the square of the value of the
periodic function taken throughout one period
3.17
shortwave broadcasting
the frequency band between 3 MHz and 30 MHz is called the short wave band. Broadcast
transmission in this frequency range is therefore called shortwave broadcasting
3.18
site
area including a short wave installation and with restricted access for public
3.19
specific absorption rate (SAR)
time derivative of the incremental energy (dW) absorbed by (dissipated in) an incremental mass (dm)
contained in a volume element (dV) of given mass density (ρ):
 
d dW d dW
 
SAR = =  
 
 
dt dm dt ρdV
 
 
SAR is expressed in units of watt per kilogram (W/kg)
3.20
transmitter
device to generate radio frequency power for the purpose of communication
4 Physical quantities and units
The internationally accepted SI-units are used throughout the standard.
Quantity Symbol Unit Dimensions
Current density J ampere per square meter A/m²
Electric field strength E volt per meter V/m
Frequency f hertz Hz
Magnetic field strength H ampere per meter A/m
Specific absorption rate SAR watt per kilogram W/kg
Wavelength λ meter m
Electric conductivity siemens per meter S/m
σ
Mass density kilogram per cubic meter kg/m³
ρ

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EN 50475:2008 – 8 –
5 Applicability of compliance assessment methods
In short wave broadcasting services, horizontally polarized, there are two field regions at the ground
level (the far field region does not exist at ground level):
– the reactive near-field region; this region is defined by r ≤ λ/4 where r is the distance from the
antenna to the point of investigation;
– the radiating near-field; this region is defined by r > λ/4 where r is the distance from the antenna
to the point of investigation.
This standard describes measurement and calculation methods to define the exposure areas and the
next tables (Table 1 and Table 2) will help to select an appropriate method.
Compliance of the results of the assessment with the appropriate reference level or action value will
ensure compliance with the relevant limit (basic restriction or exposure limit value). However, it is
always possible to test compliance directly with regards to basic restriction or exposure limit values,
both expressed in SAR and current density.
5.1 Reference level or action level values
Table 1 – Assessment methods for each antenna region
Assessment methods for each antenna region
Reactive near field Radiating near field
E and H field calculation H field calculation
a a
Induced currents calculation Induced currents calculation
Contact current calculation
E and H field measurement H field measurement
a a
Induced currents measurement Induced currents measurement
Contact current measurement
a
Compliance of maximum value of E or H field to relevant level, without spatial averaging, gives
conformity to induced current.

5.2 SAR and current density
Table 2 – Assessment methods for each antenna region
Assessment methods for each antenna region
Reactive near field Radiating near field
a
SAR and current density SAR and current density
a
No standardised method of SAR evaluation in reactive near field is available.

SAR and current density evaluation can be based either on calculated or measured field levels.

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6 SAR measurement and calculation (local and average SAR)
6.1 Approximate method for SAR calculation for frequencies below body resonance
Outside the reactive near field region, a quasi static approach is appropriate for SAR estimation when
the frequency of the wave is below the resonance frequency of a human body (around 70 MHz in free
space and 35 MHz when grounded). This approach is particularly applicable in the exposure analysis
in the near-field region of large AM-broadcast antennas.
Measurement or calculation techniques permit the determination of the electric field E and the
magnetic field H in the near field and far field of a broadcast antenna (frequency range 3 MHz to
30 MHz). For many configurations of broadcast antennas, the safety distance derived from reference
levels is overly conservative as the true absorption in the human body is much lower due to near-field
or polarisation effects. In principle, SAR-values for a human-body model may be derived by FDTD
(Finite-Difference Time-Domain) analysis when the tangential electric and magnetic field components
on a closed boundary around the body are known (Huygen’s Principle). However, it is very expensive
to assess at several locations the complete field around an appropriate volume of the human model.
Hence a practical approach has to implement some simplifications.
In general, the time-varying electric and magnetic fields are vectors and have component values with
respect to the three co-ordinate directions. However, at frequencies below resonance where the free-
space wavelength of the field is much greater than the dimensions of the human body, a quasi-static
calculation may be used for SAR assessment. When the electric and the magnetic field can be
regarded as decoupled from each other, the contribution to the SAR is determined by separate field-
component terms, each with a coefficient depending only on the incoming wave polarisation and on
the shape and conductivity of the body, expressed generally as:
SAR = a ⋅ E + b⋅ E + c⋅ E + d ⋅ H + e⋅ H + f ⋅H .
x y z x y z
For a general exposure assessment one needs to adopt an average body model to obtain
representative SAR values, or better a body model which will lead to worst-case SAR values. This is
supposed to be fulfilled by the body model of the Visible Human.
The Visible Man data set is the first result of the Visible Human Project of the National Library of
Medicine, 8600 Rockville Pike, Bethesda, Maryland, USA. It is a digital image data set of a complete
human male and consists of computed tomographic and magnetic resonance scans as well as
cryosection images.
The SAR exposure assessment gives more restrictive values compared with limit values than the
current density above a frequency range of about 3 MHz to 5 MHz.
6.2 Exposure situation
The energy absorbed by the human body is dependent on the polarisation and the direction of the
plane wave incident on the body. Following it is assumed for the model that has three semi-axes,
denoted by a, b, and c, with always a > b > c. The coordinate system is such that the greatest semi-
axis length a is always along the x-co-ordinate axis corresponding to the body length; likewise semi-
axis b is along the y-coordinate axis across the body (through the arms in a corresponding human
body model), and the shortest semi-axis c along the z-coordinate axis (from the chest to the back).
The directions of the electric field vector E, the magnetic field vector H, and the propagation vector k of
the incident plane wave are always denoted with respect to the a-, b-, and c-axes in that order. Thus,
for example, “EHk” denotes E parallel to the x-axis, H parallel to the y-axis, and k parallel to the z-axis.
For further details, see references [3] and [4].

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SIST EN 50475:2008
EN 50475:2008 – 10 –
The electromagnetic energy absorbed in the body, as expressed by the whole-body SAR, depends on
the polarisation of the incoming electromagnetic wave, and, for the standard polarisation described in
the previous paragraph, are (see reference [5], Eqq. 7-12):
EkH: SAR = SE + SH ,
wb a c
EHk: SAR = SE + SH ,
wb a b
kEH: SAR = SE + SH ,
wb b c
HEk: SAR = SE + SH ,
wb b a
kHE: SAR = SE + SH ,
wb c b
HkE: SAR = SE + SH ,
wb c a
where the quantities SE , SE , SE , SH , SH and SH are quasi-static energy-absorption
a b c a b c
components which depend only on the semi-axis lengths a, b, and c, the conductivity of the model,
and the frequency and effective field strength of the incident electromagnetic wave (see references [4]
and [5]). The parameter SE , for example, is the energy component absorbed in the body from the
a
incident electric field E polarised along the longest semi-axis a, and likewise for the H-field and the
a
other semi-axis directions b and c. For each wave polarisation above, the contribution to the whole-
body SAR is the sum of two independent components, one from the corresponding electric field and
the other from the magnetic field, which are regarded as decoupled in the quasi-static case.
This model is only applicable outside the reactive near field region of the antenna.
6.3 Polynomial expansion of “static” component values with frequency
In the quasi-static regime for a plane wave with general polarisation and direction, we have, to a good
approximation, (see reference [5]):
SAR = SE + SE + SE + SH + SH + SH .
wb x y z x y z
The SAR and “static” component values are displayed in Tables A.1 and A.2 for the inhomogeneous
Visible Human body model on the ground.
Also tabulated in Table A.3 are the coefficient values of the polynomial expansions of these quasi-
static component values as functions of frequency, between 5 MHz and 30 MHz. These permit the
determination of the quasi-static values at intermediate frequencies from those plotted. The frequency
expansions are of the form (see reference [5], Eq. 21):
3 3
n
n
SE = a f     and     SH = a f ,
∑ ∑
p n,E p n,H
p
p
n=0
n=0
where the static components are in units of mW/kg and frequency in MHz. The subscript p refers to
one of the semi-axis directions of the model, a, b or c corresponding to the usual axes x, y and z
chosen for this problem. The expansion coefficients a and a are determined by least-squares
n,E n,H
p p
fitting to the variation of each static component with frequency, and are tabulated in Table A.3 for the
body on conducting ground.

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The whole-body SAR values plotted and tabulated here are for a plane wave of incident power
1 mW/cm² = 10 W/m² r.m.s., which corresponds to an incident electric field strength of E = 61,4 V/m
io
r.m.s. and incident magnetic field strength H = 0,163 A/m r.m.s. The whole-body SAR values for
io
other effective values of incident electric and magnetic field can be determined to a good
approximation from the relationship (see reference [5], Eq. 20),
2 2 2 2 2 2
E H
           
E E H H
y y
x z x z

           
SAR = SE + SE + SE + SH + SH + SH ,
wb a b c a b c
           
E E E H H H
io io io io io io
           
where the effective values E , E , E , H , H and H can be measured incident values; or alternatively
x y z x y z
calculated incident values from some other electromagnetic calculation program. (This could be, for
example, a method-of-moments calculation which is suitable for electromagnetic fields radiated from
an antenna, and for which the field point can be taken at large distances greater than those permitted
by the memory requirements for the mesh of FDTD methods.) The above relation, and the expansions
of the static components in terms of frequency, permit the calculation to a good approximation of the
whole-body SAR for an incident plane wave, or near-plane wave, of general amplitude and
polarisation for frequencies between 5 MHz and 30 MHz for the inhomogeneous Visible Human body
model. The static components incorporate the relative permittivity and conductivity values assigned to
each tissue type for each of the frequency values 5 MHz, 10 MHz, 20 MHz and 30 MHz (see
reference [6], Table 2).
7 Current density (3 MHz – 10 MHz)
At frequencies below 10 MHz there is an additional basic restriction which must be considered, limiting
the current density in the central nervous system. The Exposure Limit Value for this is 10 A/m² at
1 MHz and increases in proportion to frequency over the frequency range up to 10 MHz.
State-of-the-art dosimetry may be used to determine the electric field that is needed to produce the
value of induced current density in the central nervous system corresponding to the exposure limit
value. For example Dimbylow (see reference [8], Table 9 and Figure 6) shows that for a grounded
person standing in a vertically polarised electric field the field must exceed 2 000 V/m before the
exposure limit is exceeded. For a person who is not grounded, even higher values of electric field
would be needed.
An electric field of 2 000 V/m is higher than the electric field that is needed to exceed of any of various
SAR exposure limits for vertically polarised electric fields.
This means that for the frequency range covered by this standard the exposure assessment does not
need to specifically consider the current density limits, provided the SAR limits are properly
considered.
This can be illustrated by referring to dosimetry computations by Findlay, Dimbylow and Mann
(reference [9]). The value of vertically polarised electric field needed to produce the Exposure Limit
Values for SAR depends on frequency and on whether or not the body is grounded, are given for
whole body average SAR, leg SAR and wrist SAR (reference [9], Table 5.3, Table 5.5 and Table 5.8
respectively). These values are all less than 2 000 V/m, and in some cases very much less than
2 000 V/m indicating that these will always be the limiting factor.
Where the electric field is predominantly horizontal it is reasonable to assume that the current density
is smaller than if the field is only vertical (which has been demonstrated for whole-body-average SAR)
and therefore the maximum electric field corresponding to the exposure limit for current density
becomes even larger.

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8 Measurement of electric and magnetic field
Measurement of electric and magn
...