Kos, B.; Valic, B.; Kotnik, T., and Gajsek, P. Exposure assessment in front of a multi-band base station antenna. Bioelectromagnetics. 2010 Dec 22.
Maintenance workers, technicians and occasionally other workers in the mobile communication industry have to work close to mobile communication base station antennas. Multi-band antennas are becoming more widespread, and assessment of exposure to electromagnetic fields is necessary for all those who may work in their vicinity. Network providers widely use three-band antennas which radiate three common mobile communication frequencies (900, 1800 and 2,100 MHz) simultaneously in space and time. Therefore, evaluation of a combined exposure gives a more complete picture than separate assessment of exposures to each frequency.
The objective was to investigate occupational exposure to electromagnetic fields in front of a multi-band base station antenna at 900, 1800 and 2,100 MHz.
The antenna model was validated against previously published measurement results using finite-difference time-domain method. This method was then used to investigate the specific absorption rate (SAR) in the Virtual Family male and female anatomical human models at distances 10-1000 mm. Combined exposure to electromagnetic fields of three different frequencies, their interaction and additivity of SAR were evaluated. Two summation approaches were compared: a simple method of summation of the maxima and a much more complicated voxel-by-voxel summation.
Results and Interpretation
At larger distances from the antenna (>200 mm), the whole body SAR is the more limiting factor for compliance with exposure guidelines. At shorter distances, the spatial-peak SAR may be more limiting. The highest frequency (2100 MHz) produces the highest localized SAR averaged over 10 g of tissue (SAR10g). For the whole body SAR, the contributions of all three frequencies are similar. The differences between exposures for the male and the female model in SAR10g are not large, while the female has a higher exposure for the whole-body SAR. The difference between the voxel-by-voxel summation and the simple summation of maxima was small.
The authors have concluded: “In evaluating simultaneous exposure to several frequencies emitted by a multi-band antenna… a simple summation of highest spatial-peak SAR values for each frequency provides a good, slightly conservative approximation of the real combined SAR.”