Specific Absorption Rate (SAR) is the unit of measurement for the amount of radio frequency (RF) absorbed by the body when using a wireless device. The SAR value is expressed in terms of watts per kilogram (W/kg) or milliwatts per gram (mW/g). The RF exposure limits used are expressed in the terms of SAR, which is a measure of the electric and magnetic field strength and power density for transmitters operating at frequencies from 300 kHz to 100 GHz. The FCC and other federal governmental agencies around the world require that any wireless device be evaluated to meet the RF exposure limits set forth in the governmental SAR regulations.
The most generally accepted method for measuring SAR values is the direct method SAR test. This method utilizes a model called a “SAM phantom” to simulate the human head and a “flat phantom” to simulate the human body. With this method, wireless devices are tested at the highest certified power level in laboratory conditions utilizing a SAR test system with a robot. An orthogonal probe is mounted on the robot arm to measure the RF fields transmitted into a calibrated tissue simulant.
The SAR testing requirement is being added to many countries around the world. Numerous other countries are in the process of evaluating the need to add SAR testing to their requirement.