skin heating of phone’s user and thermal modeling e.b. elabbassi & r. de seze drc-toxi ineris,...
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Skin Heating of Phone’s User Skin Heating of Phone’s User and Thermal Modelingand Thermal Modeling
E.B. Elabbassi & R. de SezeDRC-TOXI INERIS, Verneuil-en-Halatte,
France
•• IEEE ICES/COST 281 Thermal Physiology Workshop, 22-09-2004, INERIS
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Introduction
Mobile phone (MP) users reported feeling of discomfort, warmth behind/
around or on the ear and heat sensation of the cheek [Oftedal et al., 2000]
Thermal insulation ?
Heat conduction from the MP battery ?
Electromagnetic field (EMF) absorbed by the user’s head ?
•• IEEE ICES/COST 281 Thermal Physiology Workshop, 22-09-2004, INERIS
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Introduction
40 - 50% of the mobile phone EMF emitted
is absorbed by the user’s head [Bernardi, 2000]
The maximal absorption of the mobile phone EMF
is on the skin ~ 38.5% [Dimbylow and Mann, 1998]
•• IEEE ICES/COST 281 Thermal Physiology Workshop, 22-09-2004, INERIS
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The aim of this study is to:
quantify the temporal skin warming of the mobile phone user
compare experimental design and theoretical modeling of heat tissues distribution by the Bio-Heat Equation (BHE).
•• IEEE ICES/COST 281 Thermal Physiology Workshop, 22-09-2004, INERIS
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Materials and methods
Mobile phone GSM 1800 MHz Motorola mr 20, radiated power 125 mW,
dipole antenna
Test card
Load (50 ) : suppress the EMF exposure
Fiberoptic thermometer : Luxtron 790 F with 4 SFF-5 sensors (± 0.1°C)
Three healthy male volunteers 25, 26 and 30 years old
18 measurements were made for each trial
•• IEEE ICES/COST 281 Thermal Physiology Workshop, 22-09-2004, INERIS
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Mobile phone was held in the normal using position «cheek position»
(CENELEC standard)
3 sensors : Tair, Tskin, Tmp
Mobile phone mode:
• switched off
• switched on in reception mode
• in emission mode without load
• in emission mode with load
Tair = 23°C, Vair = 0.01 m.s-1, RH = 50 %
Temperature recorded until equilibrium was reached (30 min)
•• IEEE ICES/COST 281 Thermal Physiology Workshop, 22-09-2004, INERIS
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2 sensors face to facein a precise position on the phone and on the cheek
•• IEEE ICES/COST 281 Thermal Physiology Workshop, 22-09-2004, INERIS
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Phone held by the hand in normal user position “Cheek position”
Phone T°C
•• IEEE ICES/COST 281 Thermal Physiology Workshop, 22-09-2004, INERIS
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Efficacy of the EMF exposure suppress by switching
the RF signal from the antenna to a 50 W load (FT R&D)
SAR measurementsSAR measurements
(SAR CENELEC and IEEE limit: SAR_10g max = 2 W/kg)
•• IEEE ICES/COST 281 Thermal Physiology Workshop, 22-09-2004, INERIS
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Results
31
32
33
34
35
36
37
38
0 5 10 15 20 25 30 35 40
Time (min)
Tem
per
atur
e (°
C)
Tmp2 (°C)
Tskin2 (°C)
Tmp3 (°C)
Tskin3 (°C)
Tmp4 (°C)
Tskin4 (°C)
2 : reception; 3 : emission; 4 : emission + load
Effect of MP use on skin and MP surface temperature (Tskin, Tmp, °C)
•• IEEE ICES/COST 281 Thermal Physiology Workshop, 22-09-2004, INERIS
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Measures
Experimental conditions
Skin–phone interface
Reference Switch off Reception Emission Emission + load
Tair (°C) 22.6 ± 0.7 22.9 ± 0.8 23.1 ± 0.7 23.2 ± 0.8 23.4 ± 0.7
Tskin (°C) 33.8 ± 0.6 35. 7 ± 0.2 36.7 ± 0.2 37.1 ± 0.2 37.1 ± 0.2
Tmp (°C) 22.8 ± 0.8 35.25 ± 0.4 36.7 ± 0.2 37.2 ± 0.20 37.4 ± 0.2
T = Tskin – Tair 11.1 ± 0.7 12.8 ± 0.8 13.6 ± 0.8 13.9 ± 0.8 13.7 ± 0.7
•• IEEE ICES/COST 281 Thermal Physiology Workshop, 22-09-2004, INERIS
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Skin – phone interface temperature
+ 1.88°C+ 1.88°C
+ 3.29°C+ 3.29°C+ 2.93°C+ 2.93°C
+ 3.31°C+ 3.31°C
33
33.5
34
34.5
35
35.5
36
36.5
37
37.5
Mea
n s
kin
tem
per
atu
re (
°C)
Reference Switch off Reception Emission Emission + load
•• IEEE ICES/COST 281 Thermal Physiology Workshop, 22-09-2004, INERIS
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Conclusion
Skin heating for mobile phone users is due to:
• thermal insulation of the skin surface in contact with the MP
• conduction of the heat produced by - the battery- the RF circuits of the
phone
No significant thermal effect observed by electromagnetic field (EMF) energy absorbed by the user's head from the GSM 1800 (125 mW)
•• IEEE ICES/COST 281 Thermal Physiology Workshop, 22-09-2004, INERIS
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Modeling Bio-Heat Transfer
Heat transfer in living tissue = “Pennes’ Bio-Heat Equation” :
• Influence of blood flow
• Heat conduction in tissues
• Metabolic heat
• External heat exchanges
•• IEEE ICES/COST 281 Thermal Physiology Workshop, 22-09-2004, INERIS
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Bio-Heat Equation and Skin Heat
rmbbbb QQTTcx
Tk
t
Tc
22
2
Heat storage
Heat conduction Metabolic heat
Blood perfusion External heat
(W/m3)
•• IEEE ICES/COST 281 Thermal Physiology Workshop, 22-09-2004, INERIS
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SARQQTTcx
Tk
t
Tc rmbbbb
22
2
EM radiation absorption heat?
External heat
External heat = Heat exchange with environment
•• IEEE ICES/COST 281 Thermal Physiology Workshop, 22-09-2004, INERIS
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External heat (Qr)
Qr = ± C ± R - E
Without MP skin contact
Convection
Radiation
Evaporation
Qr = ± C ± R
•• IEEE ICES/COST 281 Thermal Physiology Workshop, 22-09-2004, INERIS
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Qr = ± K ± C ± R
With MP skin contact
Conduction
Heat insulation + Heat conduction (K)
Skin increase temperature Warmth sensation
•• IEEE ICES/COST 281 Thermal Physiology Workshop, 22-09-2004, INERIS
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Skin increase temperature
Skin blood perfusion
Skin thermal conductivity TTc bbbb
22
2
x
Tk
Skin vasodilatation (Thermoregulation)
•• IEEE ICES/COST 281 Thermal Physiology Workshop, 22-09-2004, INERIS
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Heat sensations MP user = Thermal insulation + Heat conduction.
Our results could help improve to better fit experimental data.
It seems needed to critically compare experimental design and theoretical modeling to reach a better fit between both approaches.
Conclusions
•• IEEE ICES/COST 281 Thermal Physiology Workshop, 22-09-2004, INERIS
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Acknowledgements for financial Acknowledgements for financial support:support:
Regional Council of Picardy (France)
French Ministry of Ecology and Sustainable Development (BCRD 2003, DRC02-03)
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Thank You for Attention