Specific absorption rate and temperature elevation in a subject exposed in the far-field of radio-frequency sources operating in the 10-900-MHz range

TLDR

The study computed the electromagnetic field in a heterogeneous human body model using the finite‑difference time‑domain method and evaluated temperature rise via an explicit finite‑difference bio‑heat equation. The results show that peak SAR averaged over 10 g can be 25‑fold higher in the trunk and 50‑fold higher in limbs compared to whole‑body SAR, while peak SAR over 1 g can reach up to 135‑fold in ankles, yet thermoregulation limits temperature rises to about 0.7 °C at 40 MHz for the ICNIRP permissible power density.

Abstract

The exposure of a subject in the far field of radiofrequency sources operating in the 10-900-MHz range has been studied. The electromagnetic field inside an anatomical heterogeneous model of the human body has been computed by using the finite-difference time-domain method; the corresponding temperature increase has been evaluated through an explicit finite-difference formulation of the bio-heat equation. The thermal model used, which takes into account the thermoregulatory system of the human body, has been validated through a comparison with experimental data. The results show that the peak specific absorption rate (SAR) as averaged over 10 g has about a 25-fold increase in the trunk and a 50-fold increase in the limbs with respect to the whole body averaged SAR (SAR/sub WB/). The peak SAR as averaged over 1 g, instead, has a 30- to 60-fold increase in the trunk, and up to 135-fold increase in the ankles, with respect to SAR/sub WB/. With reference to temperature increases, at the body resonance frequency of 40 MHz, for the ICNIRP incident power density maximum permissible value, a temperature increase of about 0.7/spl deg/C is obtained in the ankles muscle. The presence of the thermoregulatory system strongly limits temperature elevations, particularly in the body core.