Auteurs
Gosselin, M-C.; Christ, A.; Kuhn S.; Kuste N. Dependence of the occupational exposure to mobile phone base stations on the properties of the antenna and the human body. IEEE Transactions on Electromagnetic Compatibility. 2009 Vol. 51, No. 2, May 2009

Background

The safety guidelines for human exposure to EMFs define basic restrictions for the power absorbed in the body in terms of SAR. Since actual evaluation of SAR is possible only in laboratory conditions with body phantoms, reference levels for the strength of the incident electromagnetic fields are proposed to check for compliance with the basic restrictions. However, the correlation between the reference levels and the basic restrictions is based on simplified models for whole-body average SAR calculation or for plane-wave exposure. This makes the assessment of the local SAR difficult. The assessment of absorption is feasible using numerical simulations which encompass numerous characteristics of both the antenna and the human body and, therefore, are associated with considerable computational costs. The finite-difference time-domain (FDTD) method or hybrid technique used by several research groups yield a reduction in the computational costs. Most of these studies, however, were based on one or a very few antenna models and the visible human model.

Objective
The study was aimed at quantitative assessment of the absorption in the human body in the close proximity to mobile phone base station antennas, taking into consideration various anatomical characteristics of the exposed subject and typical parameters of base station antennas.

Methods
Numerical evaluations were conducted by using FTDT simulations. The whole-body absorption and the 10-g peak spatial average SAR were computed for three adults (55-101 kg) exposed to typical base station antennas (450-2140 MHz) at distances from 0.5 to 4 m. Validation measurements were conducted using the near-field scanner; electric and magnetic fields of the antenna were measured in free-space. The whole-body average SAR and the 10-g peak spatial average SAR were evaluated in the elliptical flat body phantom. During all measurements, the feeding power has been monitored using two power meters.

Results and interpretation
For long antennas exposing the body homogeneously, the maximum whole-body average SAR depends on the antenna input power and its horizontal half-power beamwidth, the distance from the antenna and the ratio of the cross-section of the body model to its mass. The maximum 10-g peak spatial SAR depends on various effects that fluctuate among individuals. Short antennas at short distances from the exposed individual may only expose a fraction of the body. Because peak spatial average SAR is a function of the local incident field, the probability that the local SAR determines the limit on the permissible power increases.

Conclusion
Generally, the whole-body average absorption poses limits on antenna output power. For short antennas, the peak spatial average SAR can be more restrictive than the whole-body absorption. Compliance must be demonstrated for both quantities.


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