Authors
Simba AY, Hikage T, Watanabe S, Nojima T. (2009). Absorption Rates of Anatomically Realistic Human Models Exposed to RF Electromagnetic Fields From Mobile Phones Used in Elevators. IEEE Transactions On Microwave Theory and Techniques 57(5): 1250-1259.

Background
This research addresses radiofrequency (RF) exposures from mobile phones when used in enclosed environments, such as trains, cars, and elevators.  Some reports have suggested that electromagnetic field (EMF) levels in these environments exceed the safety levels during mobile phone use.  The appearance of these reports in popular media has also increased public concern.  However, there is a lack of evidence for localized specific absorption rates (SAR) in realistic human models.  What little information exists is only for a model of a passenger’s head, while ignoring the rest of the body.

Objective
The present investigation was to determine whether the increased SAR exceeds RF-exposure guidelines when considering an adult using a mobile phone inside an elevator, with multi-reflections of electromagnetic fields from metallic walls.

Methods
Detailed SAR calculations were performed with a non-uniform mesh finite-difference time-domain technique, which minimizes computer resources.  An anatomically realistic human model was used inside an actual elevator, with the cellular phone operating at frequencies used in Japan (i.e., 900, 1,500, and 2,000 MHz).  The “worst case” considered in this paper refers to conditions that include: 1) a half-wavelength dipole antenna, placed near the head; 2) a vertically oriented dipole antenna, parallel to the sidewalls of the elevator for maximum reflection; 3) an elevator with metallic walls; and 4) a constant maximum transmitting power of 250 mW.  The dimensions of the elevator used in this study were taken from an actual elevator with maximum capacity of nine passengers. Only the simple case of one passenger using a mobile phone was considered.  The model was of a Japanese adult male of average weight and height.

Results
In an open space, as a reference, the spatial 10-g SAR values were 45%, 47%, and 57% of legislated limits (ICNIRP); i.e., 2 W/kg at 900, 1,500, and 2,000 MHz, respectively. The whole-body average SAR values were 2.6%, 1.8%, and 1.4% of the basic restriction level; i.e., 0.08 W/kg at 900, 1,500, and 2,000 MHz, respectively.  When analyzed in an elevator enclosure, the maximum 10-g SAR values obtained at 900, 1,500, and 2,000 MHz were 1.02, 1.30, and 1.56 W/kg, respectively, corresponding to an increase of 13.2%, 40.1%, and 37.6% above the reference levels.  These values were 51%, 66%, and 78% of the ICNIRP’s peak 10-g SAR restrictions.  Interestingly, destructive interference of the EMFs due to multireflections in the enclosed environment was so strong that sometimes the peak 10-g SAR of the passenger in the elevator was lower than that of the user in open space.  The maximum values of the whole-body average SAR were larger than those of the user in open space by 71%, 135%, and 188%, respectively, at 900, 1,500, and 2,000 MHz. However, these values were only 4.4%, 4.3%, and 4.1% of the ICNIRP whole-body exposure limit of 0.08 W/kg.

Discussion
Specific absorption rates were found to depend on the passenger’s position in the elevator. The results obtained indicate that the whole-body average SAR of a single mobile phone user inside an elevator will not exceed the basic restrictions recommended in the ICNIRP and IEEE guidelines.  A substantial enhancement was nevertheless observed due to multi-reflections from the elevator walls.  It would be expected that a smaller effect would be observed in other types of enclosures, such as cars and trains, because they contain absorbing materials, like seats, glass, and nonmetal walls.


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