Combining Near- and Far-Field Exposure for an Organ-Specific and Whole-Body RF-EMF Proxy for Epidemiological Research
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A framework for the combination of near-field (NF) and far-field (FF) radio frequency electromagnetic exposure sources to the average organ and whole-body specific absorption rates (SARs) is presented. As a reference case, values based on numerically derived SARs for whole-body and individual organs and tissues are combined with realistic exposure data, which have been collected using personal exposure meters during the Swiss Qualifex study. The framework presented can be applied to any study region where exposure data is collected by appropriate measurement equipment. Based on results derived from the data for the region of Basel, Switzerland, the relative importance of NF and FF sources to the personal exposure is examined for three different study groups. The results show that a 24-h whole-body averaged exposure of a typical mobile phone user is dominated by the use of his or her own mobile phone when a Global System for Mobile Communications (GSM) 900 or GSM 1800 phone is used. If only Universal Mobile Telecommunications System (UMTS) phones are used, the user would experience a lower exposure level on average caused by the lower average output power of UMTS phones. Data presented clearly indicate the necessity of collecting band-selective exposure data in epidemiological studies related to electromagnetic fields.
Technologies using electromagnetic (EM) fields are more and more employed in our society. Therefore, people are exposed to various sources in their vicinity such as mobile phones, cordless phones and base stations. In general, the contribution to personal exposure can be divided into near-field (NF) and farfield (FF) sources with respect to the human body. NF sources such as cell phones operate in close vicinity of the body and are usually controlled by the user; they can cause temporarily high local exposure. However, FF sources such as radio base stations are usually further away and thus lead to lower but rather continuous exposure levels. For a thorough study of potential specific and non-specific health effects caused by radio frequency (RF) electromagnetic fields (EMF), the contribution of different radio frequency sources to the personal exposure of different organs, body tissues, and the whole body is required. In the past, different exposure proxies were used in order to classify different exposure groups. In Neubaueret al. , the feasibility of epidemiological studies on possible health effects of mobile phone base stations was evaluated. Epidemiological studies are considered feasible if the contribution of the different sources to the RF exposure can be assessed by appropriate means such as personal exposure meters. However, the combination of FF and NF sources by weighting with exposure data collected in the corresponding study area has not been discussed so far. In this article, a reference case for combining the contributions of NF and FF radio frequency electromagnetic exposure sources to the average organ and whole-body specific exposure is investigated. Therefore, a detailed collection of numerically derived whole-body averaged (WBA) and organ-specific averaged (OSA) specific absorption rates (SARs) for NF and FF exposure scenarios are required. The corresponding SAR values are derived from numerical simulations using anatomical human body models, as presented in Christ et al. [2010a]. Although a few studies have been performed to calculate WBA and OSA SAR values for different scenarios, as in Kuehn et al. , Dimbylow et al. , Catarinucci et al. , and Meyer et al. , these results were aimed at testing compliance with given exposure limits from regulatory bodies and did not provide results of all sources that we are exposed to in everyday life. In order to close this gap, the WBA SAR and OSA SAR are calculated using the Virtual Family Model (VFM) ‘‘Duke,’’ which is considered as representative of an average male human in the population [Gosselin et al., 2011], and the SAR values provided are for both NF and FF exposure sources at the required carrier frequencies of the RF services. The NF exposure scenario is represented by a cell phone operating on the right side of the human model’s head, whereas the FF exposure scenario is characterized by the irradiation of the human model by plane waves. The normalized results from the numerical calculations are combined and weighted with the corresponding exposure values collected in the Qualifex study [Frei et al., 2009] in order to calculate the personal dose values in terms of the time-averaged SAR. The results show the relative importance of NF and FF sources to the personal exposure in the specific study area and can be used as exposure proxies in epidemiological studies on potential specific and non-specific health effects caused by RF sources.
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