Skin Heating of Phone’s User and Thermal Modeling E.B. Elabbassi & R. de Seze

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

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 ?

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]

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).

Materials and methods • Mobile phone GSM 1800 MHz Motorola mr 20, radiated power 125 mW, dipole antenna • Test card • Load (50 W) : 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

Mobile phone was heldin 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)

2 sensors face to facein a precise position on the phone and on the cheek

Phone T°C • Phone held by the hand in normal user position • “Cheek position”

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)

Results Effect of MP use on skin and MP surface temperature (Tskin, Tmp, °C) 2 : reception; 3 : emission; 4 : emission + load

Measures

37.5 37 36.5 36 + 3.29°C + 3.31°C Mean skin temperature (°C) 35.5 + 2.93°C 35 + 1.88°C 34.5 34 33.5 33 Reference Switch off Reception Emission Emission + load Skin – phone interface temperature

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)

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

Bio-Heat Equation and Skin Heat Heat conduction Metabolic heat (W/m3) Heat storage Blood perfusion External heat

External heat EM radiation absorption heat? External heat = Heat exchange with environment

External heat (Qr) • Qr = ± C ± R - E Without MP skin contact Convection Evaporation Radiation • Qr = ± C ± R

Qr = ± K± C ± R With MP skin contact Conduction Heat insulation + Heat conduction (K) Skin increase temperature  Warmth sensation

Skin increase temperature Skin vasodilatation (Thermoregulation) Skin blood perfusion Skin thermal conductivity

Conclusions • 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.

Acknowledgements for financial support: • Regional Council of Picardy (France) • French Ministry of Ecology and Sustainable Development (BCRD 2003, DRC02-03)

Thank You for Attention

Skin Heating of Phone’s User and Thermal Modeling E.B. Elabbassi & R. de Seze