What is SAR?

RF Basics 

What is Specific Absorption Rate or SAR?

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Editorial Team - everything RF

Feb 21, 2019

All the wireless devices emit radio waves which can be absorbed by the environment including our bodies. The measure of the rate of absorption, by which this RF energy is absorbed by our body while using a wireless device is called as Specific Absorption Rate (SAR).

A number of studies have concluded that RF wave exposure is harmful to our health, so the FCC (US) has set some guidelines to restrict the value of SAR below a particular level. It is mandatory for all wireless device manufacturers to follow these guidelines to get the FCC approval for their products. The FCC set SAR level for the general public is 1.6 watts per kilogram (1.6 W/kg) i.e., no mobile or wireless device must exceed the 1.6 W/kg SAR limit, in order to receive FCC certification. For example, the iPhone 6 has a Body SAR of 1.14 W/kg and Head SAR of 1.08 W/kg.

Where,

SAR = Specific Absorption Rate (in W/kg)

V = Sample Mass (in kg)

r = Position

σ (r) = Sample electricity conductivity (in S/m)

E (r) = RMS electric field (in W)

ρ(r) = Sample density (in kg/m3)

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