A measure of the rate of energy absorbed by (dissipated in) an incremental mass contained in a volume element of dielectric materials such as biological tissues SAR is usually expressed in terms of watts per kilogram (W/kg) or milliwatts per gram (mW/g) Guidelines for human exposure to RF fields are based on SAR thresholds where adverse biological effects may occur When the human body is exposed to an RF field, the SAR experienced is proportional to the squared value of the electric field strength induced in the body