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