Straume A, Oftedal G, Johnsson A (2005)

Users of cell phones often complain of warmth of the ear region while they are making a call. There may be different explanations of this. Part of the energy of the RF fields is absorbed by the tissue and may cause an increase in the skin temperature. The phone itself may act as a skin insulator. Or the temperature increase may be due to currents being drawn from the battery when the phone is switched on, causing some electrical energy to be dissipated in resistances in the phone. This leads to heating in the phone.

The authors conducted a series of experiments in a single volunteer who used a 900 MHz phone for up to 30 minutes at a time. The subject held the phone in the usual position. Various situations were tested. These included the phone switched off, or switched on but the RF exposure eliminated, or with the RF fields transmitting. The output power could be adjusted, and the minimal (0.002 W) and the maximal (0.21 W) power levels of the phone were used. In the maximal power situation, the SAR for 1g was 0.81 W/kg in the cheek area and 0.70 W/kg in the ear area. The study was conducted on 5 consecutive days, with 6 different experiments done each day, separated by rest periods. The order of the different exposure conditions was changed each day, so that each condition was presented at all the different times of the day, and each condition had been preceded by each of the other conditions. The study was double blind. An infrared camera was used to assess the skin temperature. The temperature changes after 15 and 30 minutes of phone use were calculated on the exposed side of the head relative to the unexposed side.

The insulation and the electrical power dissipation led to statistically significant rises in the skin temperature, while the RF exposure did not.

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