Microwave dosimetry in biological exposure studies and in practical safety evalutations

This thesis considers the risk evaluation of microwaves from two important points of view. First, the methodology of the exposure studies elucidating the health effects of mobile phones is considered starting from the general aspects of designing setups and proceeding to the assessment of the exposure level (dosimetry) and practical execution of the experiments. Second, the exposure assessment in practical safety evaluations of fixed radio transmitters, such as mobile phone base stations, is studied. The dosimetry and the exposure setup design are critical for the success of exposure studies since the biological results are worthless if the used exposure level is not known. Furthermore, the experiments with test animals or human volunteers are always very challenging in practice. This work aimed to design, implement and analyse setups for four separate biological experiments. The first experiment related to a novel study of the effects of mobile phone (GSM) radiation in human skin in vivo. In the second experiment the brain functions of domestic pigs exposed to high level GSM type radiation were studied. The third setup was used for long term exposure of over 200 unrestrained rats. The rat setup was further utilised in another experiment searching the effects of microwave radiation on central nervous system of juvenile rats. The dosimetric analysis was performed by means of numerical simulations in all cases. The simulations were validated by measurements and the uncertainty of achieved results was analysed. The functionality of the setups was proven in practice; all experiments were successfully executed and the results of both methodological and biological studies were reported in peer reviewed journals. The need for microwave safety evaluations has increased quickly during the last decade. The number of base station (BS) antennas has increased rapidly and they are often placed on roof tops etc. where various professionals have to work. Hence, efficient methods for assessing the compliance with exposure limits are needed. The scope of the work, presented in this thesis, was to study the near field exposure caused by real commercial BS models. Experimental measurements were utilised to achieve a set of specific absorption rate (SAR) and electric field data in the near field of six commonly used antenna models. Moreover, one of the antennas was studied in more detail by numerical simulations. The results were further analysed to compare the different methods for checking the compliance of an antenna installation with the exposure limits and to find out how significant the local exposure is as compared to the whole body average at different distances. These results provide useful information for the future revisions of the exposure limits and related measurement standards.