Based on a recommendation from industry group IEEE, the FCC limits SAR levels for partial-body exposure (including the head) to up to 1.6 W/kg (watts/kilogram), and whole body exposure to up to 0.08 W/kg. For hands, wrists, feet and ankles, the limit is up to 4 W/kg, averaged over 10 grams of tissue.
In general, the lower the SAR, the better the chances your phone is not a potential health hazard. To test the SAR, a mold in the shape of a human head is filled with a fluid formulated to simulate the electrical properties of the human tissue. This fluid typically is made up of salt, sugar, water and a viscosity additive.
The model for the human head is called SAM (standard anthropomorphic model). The size of the head is based on on the 90th-percentile dimensions of the male head, as determined by a study of U.S. Army personnel in the late 1980s — in other words, it’s a big head. Overall ambient temperature and humidity of the testing chamber is also controlled. In this case, the ambient temperature was at 70.7 degrees Fahrenheit and the relative humidity was 36.1 percent, approximating a beautiful fall day in the San Francisco Bay Area.
The first step in the testing process is to strap a phone (the iPhone in this case) to the head mold. The phone is taped to the mold in a way such that the antenna of the phone is positioned near the jaw. The testing system consists of a computer-controlled probe, a robotic arm, amplifier output that connects to a PC and a cable that connects to a universal radio communication tester.
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