(A) study on the evaluation of human exposure levels to RF electromagnetic field radiated from radio base stations

Abstract

In recent years, due to a dramatic increase in the number of radio base stations, there has been a growing public concern about exposure to the electromagnetic fields (EMF) radiated from such stations. In order to protect people from potential hazards that might be caused by EMF energy emissions from base station antennas, the International Commission on Non-Ionizing Radiation Protection (ICNIRP) has recommended levels of exposure, basic restrictions and reference levels, which many nations have adopted as their EMF safety limits for occupational workers and the general public. Additionally, related to the assessment of human exposure in the far field region, ICNIRP recommends a whole-body averaged assessment, called spatial averaging. In the far field region, the wave front of an EMF is theoretically assumed to be flat. However, due to the multi-path formed between the EMF source and the investigation location, the field values vary spatially. This is why we should consider a spatial averaging process. When an exposure measurement is carried out in the far field region, we generally evaluate the reference levels that apply to a situation in which the EMF is not influenced by the presence of a body. However, it is impossible to measure throughout the spaces occupied by a whole body to obtain spatially averaged value. Therefore, the determination of the number of measurement points is very important since the mean value varies with those used in averaging process. Even though there had been many related research with averaging process, the standard method would have not established so far. Related to the measurement time, in order to evaluate human exposure to radio base stations, the ICNIRP guidelines recommend that the reference levels at any point be averaged over any 6 min period for the frequencies between 100 kHz and 10 GHz. The averaging time means the appropriate time over which exposure is averaged for the purpose of determining compliance with exposure...