Determination of safety distance limits for a human near a cellular base station antenna, adopting the IEEE standard or ICNIRP guidelines

Abstract

This paper investigates the minimum distance for a human body in the near field of a cellular telephone base station antenna for which there is compliance with the IEEE or ICNIRP threshold values for radio frequency electromagnetic energy absorption in the human body. First, local maximum specific absorption rates (SARs), measured and averaged over volumes equivalent to 1 and to 10 g tissue within the trunk region of a physical, liquid filled shell phantom facing and irradiated by a typical GSM 900 base station antenna, were compared to corresponding calculated SAR values. The calculation used a homogeneous Visible Human body model in front of a simulated base station antenna of the same type. Both real and simulated base station antennas operated at 935 MHz. Antenna-body distances were between 1 and 65 cm. The agreement between measurements and calculations was excellent. This gave confidence in the subsequent calculated SAR values for the heterogeneous Visible Human model, for which each tissue was assigned the currently accepted values for permittivity and conductivity at 935 MHz. Calculated SAR values within the trunk of the body were found to be about double those for the homogeneous case. When the IEEE standard and the ICNIRP guidelines are both to be complied with, the local SAR averaged over 1 g tissue was found to be the determining parameter. Emitted power values from the antenna that produced the maximum SAR value over 1 g specified in the IEEE standard at the base station are less than those needed to reach the ICNIRP threshold specified for the local SAR averaged over 10 g. For the GSM base station antenna investigated here operating at 935 MHz with 40 W emitted power, the model indicates that the human body should not be closer to the antenna than 18 cm for controlled environment exposure, or about 95 cm for uncontrolled environment exposure. These safe distance limits are for SARs averaged over 1 g tissue. The corresponding safety distance limits under the ICNIRP guidelines for SAR taken over 10 g tissue are 5 cm for occupational exposure and about 75 cm for general-public exposure.

The relation between SAR and the electromagnetic field distribution for heterogeneous exposure conditions

“…mobile phone base stations, are usually heterogeneous for real life conditions due to multipath propagation, shadowing effects, impact of the environment and under certain circumstances due to the interaction between the human body and the antenna system. The existing scientific body of information on this topic is limited, mainly focuses on reactive near field exposure conditions and is not adequate to draw final conclusions [5][6][7][8][9][10][11][12]16]. The aim of this project is therefore the provision of measurement and calculation data to establish a correlation between basic restrictions, incident electromagnetic fields and optimized free space measurement technologies.…”

Specific absorption rate and electric field measurements in the near field of six mobile phone base station antennas

“…The number of BS antennas is very large, hence fast and effective exposure assessment methods are needed for ensuring compliance with applicable safety limits. Therefore, studies have been conducted to develop numerical methods and measurement procedures to assess the safety distance of certain installations and to assess the safety distances of commercial BS antenna models [Blanch et al, 2002;CENELEC, 2002;Cooper et al, 2002;Joseph and Martens, 2005].…”

Radio frequency electromagnetic field compliance assessment of multi‐band and MIMO equipped radio base stations

“…These standards contain general specifications, with limited guidance on practical issues related to modeling and simulations of RBS antennas. In the literature, numerical SAR assessments have been reported in a number of studies using various techniques [Cooper et al, 2002;Joseph et al, 2003; respectively. Compliance with the exposure limits at the assessment point is obtained if is below one.…”

“…These standards contain general specifications, with limited guidance on practical issues related to modeling and simulations of RBS antennas. In the literature, numerical SAR assessments have been reported in a number of studies using various techniques [Cooper et al, 2002;Joseph et al, 2003;Joseph and Martens, 2005;Martínez-Búrdalo et al, 2005;van Wyk et al, 2005;Kos et al, 2011]. Results from numerical SAR simulations, evaluated against the basic restrictions, have also been compared with power density results, evaluated with respect to the reference levels [Dimbylow, 2002;Lacroux et al, 2008;Thielens et al, 2013].…”