What is SAR?
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Specific Absorption Rate (SAR) is a dosimetric quantity and is defined
as the rate at which RF energy is absorbed per unit mass of biological tissue.
RF dosimetry is the quantification of the magnitude and distribution of
absorbed electromagnetic energy within human and biological objects that are exposed to electromagnetic radiation (EMR).
SAR Units of measurement
SAR is measured in units of
- Watts per kilogram [W/kg] or
- milliWatts per gram [mW/g]
SAR Standards Limits
In most countries, for devices used at the head, torso or any part of
the body (excluding the hands, wrists, feet and ankles), most standards
(EN50360/1, ACA, ARIB) set a SAR limit of 2 W/kg measured in a 10 g
mass of tissue.
The FCC (USA) sets a SAR limit of 1.6 W/kg measured in a 1 g mass of
tissue.
Because the 1 g tissue mass in which the RF energy is absorbed is much
smaller than the 10 g mass, this leads to a much greater temperature
rise, therefore, the FCC limit is effectively much tougher than the rest
of the world.
At 1800 MHz, a device that gives a
SAR of 1.6 W/kg in a 1 g mass of tissue will typically give a SAR of 0.8
W/kg in a 10 g mass of tissue.
Devices that comply with one SAR standard may
not necessarily comply with another SAR standard.
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