Purpose of SAR Measurements

What is SAR(Specific Absorption Rate)?
SAR is formed from the initials of the words “Specific Absorption Rate”. It is expressed as the amount of electromagnetic power absorbed per unit mass of the body during the use of a mobile telephone. Its unit is W / kg . Determination of SAR by the electric field strenght method is used in commercial radiating devices.

Purpose of SAR Measurements
SAR values of mobile phones are checked by the ICTA SAR Laboratory measurements whether they are appropriate for the market or not according to the values of European Commission’s determined SAR limit of 2 W/kg.
The SAR values of mobile phones below 2 W / kg are eligible to circulate in the market, while devices that exceed this value are considered to be inappropriate.


SAR Limits
There is 2 different SAR limits used in the World and 2 different guides for them.


  Whole Body SAR Local SAR Average Time Average Mass
ICNIRP 0,08 W/kg 2 W/kg 6 minutes 10 gram
FCC 0,08 W/kg 1,6 W/kg 10 gram 1 gram

Head part is considered to be the local SAR and SAR limit is determined as 2 W/kg by ICNIRP for ( International Commission on Non- Ionizing Radiation Protection) and 1.6 W/kg by FCC (Federal Communications Commision).
Turkey, European Union member countries and the majority of the countries of the world accept ICNIRP’s limit of 2 W/kg.
United States and some countries such as Canada accepts the FCC limits . FCC set limits according to IEEE standard that was released in 1991. However, IEEE, in 2005 , recognized the limits that ICNIRP applied by deciding a mutual work in standard operations. As a result of this occcasion, some countries that implemented the FCC limits began to apply the ICNIRP limits , but countries like the US and Canada continue to use the old limit.

Theoretical Termal Value
Mathematically,

J ( J / kg) = exposure time x SAR (W / kg ) ( seconds )

From the formula above, absorbed energy amount in a unit mass that was exposed to threshold value of 2 W/kg for 30 minutes is:

J ( J / kg) = 2 x 30 x 60 3600 J/kg According to the formula showing the temperature increase, the energy is:

t = Temperature increase ( ° C)
J = Specific energy absorption ( J / kg)
c = Relative Heat Capacity ( 0.85 ) to


t = J/(c × 4180)
t = 3600/(0,85 x 4180)
t = ~1 °Ctemperature increase occurs (In the worst scenario, the reaction of body for self-cooling was neglected.) [1].

Photon energy of RF electromagnetic waves is not sufficient to ionize atoms and molecules. Thermal effects can occur in live beings as a result of exposing non-ionizing electromagnetic waves of mobile phones: Thermal effects is defined as conversion of electromagnetic energy absorbed by body to heat and by the way, increasing the body temperature. This temperature increase continues until the balancing of body heat which thrown by the blood flow. In reality, the temperature increase in human body by RF sources like mobile phones is very low and probably they can be disabled easily with the body's normal mechanisms. The temperature rise may occur in the brain with an average mobile phone is around 0.1 ° C [2].

SOURCES
[1]-Saunders, R. D. et al., Biological effects of exposure to non-ionising electromagnetic fields and radiation: 3 Radiofrequency and Microwave Radiation; Report NRPB-R240 December 1991; ISBN 0–85951–332–7, HMSO Books, London.
[2]-TÜBİTAK-BİLTEN, 2001, Elektromanyetik Dalgalar ve İnsan Sağlığı-Sıkça Sorulan Sorular ve Yanıtları

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