Vermeeren G, Gosselin MC, Kühn S, Kellerman V, Hadjem A, Gati A, Joseph W, Wiart J, Meyer F, Kuster N, Martens L. (2010). The influence of the reflective environment on the absorption of a human male exposed to representative base station antennas from 300 MHz to 5 GHz. Phys Med Biol. 55(18):5541-55.
Specific absorption rate (SAR), a measure of exposure to radiofrequency electromagnetic fields (EMF), is strongly influenced by the environment. This study focuses on the influence of reflective environments on the absorption for base station antenna exposure. Previous studies have mostly looked at GSM or UMTS frequencies on general public exposure and the influence of the environment on the absorption for base station antennas.
The study assessed numerically the variation of the induced SAR in the human body due to the environment. The objective of the study is to carry on the development of IEC standard PT62232 by investigating reflective environments. It focused on occupational exposure because the human body model was placed at close distances of base station antennas (-10 m).
The human body model was placed at four different distances in front of a base station antenna in three different reflective environments; 72 configurations (3 environments, 4 separations and 6 frequencies). The three reflecting scenarios were (1) perfectly conducting ground (denoted as ground), (2) perfectly conducting wall (denoted as wall) and (3) the combination of perfectly conducting ground and wall (denoted as ground + wall). A total of six base station antennas operating at frequencies between 300 MHz to 5 GHz were used in the study. The inhomogeneous virtual family male (VFM) was chosen as the human body model; the FDTD technique assessed the SAR in the male model.
A ratio was used of the different reflective environments and free-space to assess the variation on the whole-body and peak spatial averaged SAR. The largest ratios occurred at low frequencies ranging from −8.7 dB to 8.0 dB. For the majority of the configurations, the highest SAR values for both whole-body and peak 10 g compared to free-space environment were for the reflective environments with a wall. Whole-body averaged SAR complied with the reference levels with the basic restrictions for the configurations studied. But, for the peak spatial averaged SAR in the trunk and the limbs, it was found that the basic restrictions were exceeded (when the average incident power density equals the reference level in several configurations).
The whole-body SAR and peak spatial averaged SAR were determined in the virtual family male in a perfectly conducting environment of base station antennas (300–5,000 MHz). The ratio of SARwb and peak SAR10 g in a perfectly reflecting environment and free space was frequency dependent and varies, above resonance, between −4 dB and 6 dB in this investigation. Variations presented in past experiments were also within the range found in this study.
It was concluded that the whole-body and local absorption varied considerably compared to the absorption in the virtual family male placed in a free space environment. The ICNIRP reference levels are not always conservative in a reflective environment, for the basic restrictions in a reflective environment. It is true for separation distances of up to 1 metre between base station antennas and virtual family male model.