general public exposure to electromagnetic fields ... public exposure to electromagnetic fields...
TRANSCRIPT
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General public exposure to electromagnetic fields generated by mobile phone base stations:
A simple model
Hugo Lehmann1, Ulrich Herrmann1, Bernhard Eicher1, Alain Trostel1, Peter Fritschi1, Mirjana Moser2
1Environment & Electromagnetic Compatibility, Swisscom Innovations, CH-3050 Bern
2Federal Office of Public Health, Radiation Protection Division, CH-3003 Bern, Switzerland
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H. Lehmann, cost281 workshop on exposure assessment, Paris 20/9/04
Agenda:
Motivation
Model properties
Results: – field distributions – probability density distributions – medians / parts of populations exposed over 1 V/m
Extrapolation to different average powers per cell
Conclusions
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H. Lehmann, cost281 workshop on exposure assessment, Paris 20/9/04
Motivation:
Assessment of electromagnetic fields (EMF) generated by mobile phone networks: by measurements?
– huge spatial variations (interference) – temporal changes (traffic, uncontrolled parameters) of the signal
strength – quite important uncertainty – results depend on the chosen measurement procedure / equipment
measurements give only extremely restricted information on the average exposure
Time demanding > high costs
It is almost impossible to get the necessary data for exposure classification for epidemiological studies solely by measurements
Personal dosimeters have yet to prove validity and liability
exposure assessment by calculations
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H. Lehmann, cost281 workshop on exposure assessment, Paris 20/9/04
Simple free space propagation model:
24 dEIRPS
⋅=
πI equals II
0
2
µcEHES =⋅=
I
γδ ⋅=
ERPd
E 7
II
III
Attenuation factors δ and γ : − δ: attenuation of the construction materials: set to 1− γ: attenuation characteristics of the antenna as provided by
the antenna manufacturer Eq. III is used in Swiss regulation for the estimation of the electrical fields generated by a BS before its construction
Average E-field strength
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H. Lehmann, cost281 workshop on exposure assessment, Paris 20/9/04
Region of interest (i), Bern north, suburban area:
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H. Lehmann, cost281 workshop on exposure assessment, Paris 20/9/04
Further assumptions of the model/restrictions:
Only base stations of the Swisscom mobile network have been included in the calculations
Neglecting topographical data, a flat surface was adopted.
Geometrical properties: relative distance of antennas, height and main beam directions have been taken into account
No absorption due to construction materials and no shadowing effect have been considered
Calculation of the electrical field at 1.5 m over ground
The contributions of the different base stations have been summed up according to (n=# of base stations):
∑=
=n
iiEE
1
2
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H. Lehmann, cost281 workshop on exposure assessment, Paris 20/9/04
Region of interest (ii), Zurich City, urban aera:
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H. Lehmann, cost281 workshop on exposure assessment, Paris 20/9/04
Properties of the chosen areas:
1218# of base stations
GSM & UMTS:march 04
GSM: summer 03UMTS: march 04
Status of network
urbansuburbanDemographical type
5528 persons/km21734 persons/km2Population density
445041’615Inhabitants
0.805 km224 km2area
Zurich CityBern NorthRegion of interest
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H. Lehmann, cost281 workshop on exposure assessment, Paris 20/9/04
Time averaged emitted power:
BCCH
TCH
100%: maximal power
Time of day24:000:00 12:00
Emitt
ed p
ower
BCCH
TCH 1
TCH 2 TCH 2
35
4
43
3
60
2
25
6
2528Average ERP in % of the maximal ERP
UMTS5Number of carriers of the cell GSM
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H. Lehmann, cost281 workshop on exposure assessment, Paris 20/9/04
Results (i): field distributions, Bern north
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H. Lehmann, cost281 workshop on exposure assessment, Paris 20/9/04
Region of interest (i), Bern north, suburban area:
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H. Lehmann, cost281 workshop on exposure assessment, Paris 20/9/04
Results (i): field distributions, Zurich City
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H. Lehmann, cost281 workshop on exposure assessment, Paris 20/9/04
Results (ii): probability density distributions: GSM
0
1
2
3
4
5
6
7
0.00 0.10 0.20 0.30 0.40 0.50 0.60 0.70 0.80 0.90 1.00
Electrical field strength [V/m]
% o
f p
op
ula
tio
n in
th
e b
in
Bern North Zurich City Fit with a lognormal distribution
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H. Lehmann, cost281 workshop on exposure assessment, Paris 20/9/04
Results (ii): probability density distributions: UMTS
0
2
4
6
8
10
12
14
0.00 0.10 0.20 0.30 0.40
Electrical field strength [V/m]
% o
f p
op
ula
tio
n in
th
e b
in
Bern North
Zurich City
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H. Lehmann, cost281 workshop on exposure assessment, Paris 20/9/04
Results (iii): characteristic numbers
Suburban Bern North
Urban Zurich City
Network GSM UMTS GSM UMTS
Proportion of the population exposed to more than 1 V/m [%]
0.12 0 0.80 0
Median exposure [V/m] 0.18 0.10 0.58 0.18
How does the system behave for different average powers of the cells?
Assuming that the population density over the field strength shows a lognormal behaviour (as for the GSM-system), an extrapolation to higher average powers per cell was done.
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H. Lehmann, cost281 workshop on exposure assessment, Paris 20/9/04
Extrapolation to different average powers per cell (i): probability distributions
0
1
2
3
4
5
6
7
0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1 1.1 1.2 1.3 1.4
Electrical field strength [V/m]
% o
f p
op
ula
tio
n i
n t
he
bin
Bern North
Fit with a lognormal distribution; P=P0
P/P0=2
P/P0=4
P/P0=10
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H. Lehmann, cost281 workshop on exposure assessment, Paris 20/9/04
Extrapolation to different average powers per cell (ii): cumulated distributions
0.00%
10.00%
20.00%
30.00%
40.00%
50.00%
60.00%
70.00%
80.00%
90.00%
100.00%
0.00 0.20 0.40 0.60 0.80 1.00 1.20 1.40 1.60 1.80 2.00
Electrical field strength [V/m]
% o
f p
op
ula
tio
n e
xpo
sed
to
less
th
anth
e g
iven
fie
ld s
tren
gth
actual power P0
P/P0=2
P/P0=4
P/P0=10
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H. Lehmann, cost281 workshop on exposure assessment, Paris 20/9/04
Extrapolation to different average powers per cell (iii) : Results
0.00
2.00
4.00
6.00
8.00
10.00
12.00
14.00
0.1 0.5 1.5 2.5 3.5 4.5 6 8 10
P/P0
% o
f p
op
ula
tio
n e
xpo
sed
to
mo
re t
han
1 V
/m
0
0.1
0.2
0.3
0.4
0.5
0.6
Med
ian
exp
osu
re [V
/m]
Characteristic numbers change rapidly with changing power of thecellsThe extrapolation is only valid if the network structure remainsidentical.
P/P0=4:- % over 1 V/m: 2%- median exposure: 0.36 V/m
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H. Lehmann, cost281 workshop on exposure assessment, Paris 20/9/04
Conclusions:
The proposed model based on data used for regulation purposes allows for an estimation of the general public exposure to EMF generated by mobile phone networks.
Time averaged exposition is generally much lower than 1 V/m.
Characteristic numbers can easily be calculated: – median field strength – proportions of the population exposed to a given field
strength
These characteristic numbers change rapidly with changing radiated power per cell.
Improvements by integration of the topographical information andthe average attenuation of construction materials