Topic

Determination of the real exposure from using mobile phones in partially shielded rooms as compared to exposure under optimal conditions outdoors

Start

01.12.2004

End

31.07.2006

Project Management

Engineering Company Telekom-Consult

Objective

The hypothesis that wireless telecommunication in partially shielded rooms (e.g. in vehicles, on the train etc.) leads to increased exposure to high frequency electromagnetic fields had to be examined within this project. In order to do this, the real exposure in partially shielded rooms had to be determined and compared to those values found under more suitable transmission conditions outdoors.

Results

Numerical computer simulations carried out within the project showed that even quite a few number of mobile phones operated within partially shielded rooms (e. g. car, bus, train, etc.) do not cause any violation of recommended exposure limits. Because of reflections and superpositions of signals, electric field strengths in the order of some 10 V/m can be found at some places, but there are no indications that basic restrictions in terms of SAR (neither whole body averaged nor peak 10 g average SAR) will be exceeded. Computations were carried out assuming maximum transmission power of the mobile phones according to GSM 900, GSM 1800 and UMTS specifications, respectively. The computations showed that the maximum local exposure of a mobile phone user (in terms of maximum 10 g averaged SAR in the head) basically results from his own mobile phone. Assuming that all mobile phones operate at identical maximum power levels (i. e. neglecting power control mechanisms), the user’s own mobile phone is “the almost only relevant source of exposure”. In contrast to maximum 10 g averaged SAR values these values depend on the number and on the distance of transmitting mobile phones in the vicinity. This holds true for both mobile phone users and non-users (persons who are inside a room but do not use a mobile phone). However, even under worst case conditions with regard to the number of people using their mobile phone simultaneously inside a room, these values are always lower compared to the 10 g averaged values that are relevant in terms of exposure limits. As a matter of fact, the SAR values averaged over the entire head region are already lower by a factor greater than 10 compared to recommended limit values for whole body exposure conditions. As a consequence violations of recommended limit values for whole body exposure can be ruled out. However, for non-users the transmitting mobile phones in their nearby surrounding represent the relevant source of exposure. For the non-users’ exposure it is of some relevance, whether a scenario is situated within a partially shielded room or in a similar situation outdoors. SAR values within the room may be one order of magnitude higher than outdoors. However, as absolute values are at least two orders of magnitude, according to computations carried out, lower compared to values obtained for mobile phone users, one can say, that exposure is generally quite low. For mobile phone users the question whether a scenario is looked at within a partially shielded room or in a similar situation outdoors is of much less importance, if effects of power regulation are neglected. In realistic scenarios the maximum increase of 10 g averaged peak SAR values inside the user’s head caused by the presence of reflecting elements was found to be 15 % only.

In addition to the impact on maximum possible exposure values induced by reflections and contributions of mobile phones that are operated by users nearby, the actual effective exposure is determined also by automatic power regulation in cellular mobile phone nets. This aspect was analyze by means of measurements within and outside of various partially shielded rooms. Basically the measurements confirmed, that the user’s exposure increases within partially shielded rooms compared to similar scenarios outside because of increased usage of higher transmission power levels (e.g. measurements within a car showed that power levels are increased by a factor of up to four on an average).

Final Report (part 1) (4.886 KB) in German.

Final Report (part 2) (5.920 KB) in German.

Erratum (18 KB) in German.

Conclusion

In principle exposure to high frequency electromagnetic fields may increase when mobile phones are operated within partially shielded rooms. No evidence was found that recommended exposure limits could be exceeded for persons, who do not use a mobile phone themselves.