Skin Heating of Phone’s User and Thermal Modeling E.B. Elabbassi & R. de Seze DRC-TOXI INERIS, Verneuil-en-Halatte, France

IEEE ICES/COST 281 Thermal Physiology Workshop, , INERIS 2 / 22 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, , INERIS 3 / 22 Introduction  % 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, , INERIS 4 / 22 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, , INERIS 5 / 22 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, , INERIS 6 / 22  Mobile phone was held in the normal using position «cheek position» (CENELEC standard)  3 sensors : T air, T skin, T mp  Mobile phone mode: switched off switched on in reception mode in emission mode without load in emission mode with load  T air = 23°C, V air = 0.01 m.s -1, RH = 50 %  Temperature recorded until equilibrium was reached (30 min)

IEEE ICES/COST 281 Thermal Physiology Workshop, , INERIS 7 / 22 2 sensors face to face in a precise position on the phone and on the cheek

IEEE ICES/COST 281 Thermal Physiology Workshop, , INERIS 8 / 22 Phone held by the hand in normal user position “Cheek position” Phone T°C

IEEE ICES/COST 281 Thermal Physiology Workshop, , INERIS 9 / 22 SAR measurements Efficacy of the EMF exposure suppress by switching the RF signal from the antenna to a 50 W load (FT R&D) SAR measurements (SAR CENELEC and IEEE limit: SAR_10g max = 2 W/kg)

IEEE ICES/COST 281 Thermal Physiology Workshop, , INERIS 10 / 22 Results 2 : reception; 3 : emission; 4 : emission + load Effect of MP use on skin and MP surface temperature (T skin, T mp, °C)

IEEE ICES/COST 281 Thermal Physiology Workshop, , INERIS 11 / 22 Measures Experimental conditions Skin–phone interface ReferenceSwitch offReceptionEmissionEmission + load T air (°C)22.6 ± ± ± ± ± 0.7 T skin (°C)33.8 ± ± ± ± 0.2 T mp (°C)22.8 ± ± ± ± ± 0.2  T = T skin – T air 11.1 ± ± ± ± ± 0.7

IEEE ICES/COST 281 Thermal Physiology Workshop, , INERIS 12 / 22 Skin – phone interface temperature °C °C °C °C Mean skin temperature (°C) ReferenceSwitch offReceptionEmissionEmission + load

IEEE ICES/COST 281 Thermal Physiology Workshop, , INERIS 13 / 22 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, , INERIS 14 / 22 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, , INERIS 15 / 22 Bio-Heat Equation and Skin Heat Heat storage Heat conduction Metabolic heat Blood perfusion External heat (W/m 3 )

IEEE ICES/COST 281 Thermal Physiology Workshop, , INERIS 16 / 22 EM radiation absorption heat? External heat External heat = Heat exchange with environment

IEEE ICES/COST 281 Thermal Physiology Workshop, , INERIS 17 / 22 External heat (Q r ) Q r = ± C ± R - E Without MP skin contact Convection Radiation Evaporation Q r = ± C ± R

IEEE ICES/COST 281 Thermal Physiology Workshop, , INERIS 18 / 22 Q r = ± 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, , INERIS 19 / 22 Skin increase temperature Skin blood perfusion Skin thermal conductivity Skin vasodilatation (Thermoregulation)

IEEE ICES/COST 281 Thermal Physiology Workshop, , INERIS 20 / 22  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, , INERIS 21 / 22 Acknowledgements for financial support:  Regional Council of Picardy (France)  French Ministry of Ecology and Sustainable Development (BCRD 2003, DRC02-03)

IEEE ICES/COST 281 Thermal Physiology Workshop, , INERIS 22 / 22 Thank You for Attention