Assessment of specific absorption rate (SAR) and temperature increases in the human head of portable telephones

The bioheat equation is solved for an anatomically based model of the human head with a resolution of 2.5× 2.5 ×2.5 mm to study the thermal implications of exposure to electromagnetic (EM) fields typical of cellular telephones at 900 MHz. Attention has first been posed on a particular phone model, and a comparison between the absorbed power distribution and steady-state temperature increases has been carried out. The antenna output power was set to be consistent with the portable telephones of 600 mW, maximum SAR values, averaged over 1 gm, from 2.1 to 3.6 W/kg depending on the considered phone. The maximum temperature increases are obtained in the ear and vary from 0.22°C to 0.39°C, while the maximum temperature increases in the brain lie from 0.07°C to 0.17°C. These steady-state temperature increases are obtained after about 48 min of exposure, with a time constant of approximately 6 min. Application of the ANSI/IEEE safety guidelines restricting the 1 gm averaged spatial peak SAR to 1.6 W/kg results in the maximum temperature rise in the brain from 0.07°C to 0.15°C at 900 MHz. Finally, considerations about the exposure limits in the considered frequency are made.