Statistical perturbations in personal exposure meters caused by the human body in dynamic outdoor environments

Abstract

Personal exposure meters (PEM) are routinely used for the exposure assessment to radio frequency electric or magnetic fields. However, their readings are subject to errors associated with perturbations of the fields caused by the presence of the human body. This paper presents a novel analysis method for the characterization of this effect. Using ray-tracing techniques, PEM measurements have been emulated, with and without an approximation of this shadowing effect. In particular, the Global System for Mobile Communication mobile phone frequency band was chosen for its ubiquity and, specifically, we considered the case where the subject is walking outdoors in a relatively open area. These simulations have been contrasted with real PEM measurements in a 35-min walk. Results show a good agreement in terms of root mean square error and E-field cumulative distribution function (CDF), with a significant improvement when the shadowing effect is taken into account. In particular, the Kolmogorov-Smirnov (KS) test provides a P-value of 0.05 when considering the shadowing effect, versus a P-value of 10⁻¹⁴ when this effect is ignored. In addition, although the E-field levels in the absence of a human body have been found to follow a Nakagami distribution, a lognormal distribution fits the statistics of the PEM values better than the Nakagami distribution. As a conclusion, although the mean could be adjusted by using correction factors, there are also other changes in the CDF that require particular attention due to the shadowing effect because they might lead to a systematic error.

Calibration and uncertainties in personal exposure measurements of radiofrequency electromagnetic fields

“…The ability of the body-worn exposimeters to accurately measure the ambient EMF has been discussed in a number of papers. In broad terms, these either measure response of the RF exposimeter to a standard input signal [Mann et al, 2005;Lehmann et al, 2006;Radon et al, 2006;Knafl et al, 2008;Bornkessel et al, 2010;Lauer et al, 2010], or model the influence of the body [Blas et al, 2007;Iskra et al, 2007Iskra et al, , 2010Bahillo et al, 2008;Joseph et al, 2008;Neubauer et al, 2008Neubauer et al, , 2009Vermeeren et al, 2008Vermeeren et al, , 2010Roderíguez et al, 2011].…”

Assessment of human body influence on exposure measurements of electric field in indoor enclosures

“…The proposed simulation model provides acceptable results in terms of the RMSE [Rodríguez et al, ]. But the optimal value of the shadow angle has been selected taking into account the result of the KS test that is a better indicator in evaluating the accuracy of the model since RMSE metrics penalize small spatial displacements related to electric path‐length uncertainties [Blas et al, ].…”

“…For diffraction modeling, we employed an extension of Holm's heuristic diffraction coefficient proposed by Nechayev and Constantinou [2006] (that has been used in the simulation of outdoor environments in other studies [Rodríguez et al, 2011]).…”

“…Many studies have tried to quantify the effect of the human body on the measurement data obtained by PEMs. It must be stressed that the BSE influence on the PEMs’ measurements is different in indoor [Neubauer et al, ] and outdoor environments [Knafl et al, ; Bolte et al, ; Rodríguez et al, ]. It is predictable that the influence of the human body is greater in open spaces than in indoor enclosures, but as will be shown later, in indoor environments the BSE does not produce a negligible effect, and should be taken into account in the analysis of the exposure conditions of humans to EMF.…”

“…This work analyzes the influence of the BSE in the PEM readings. Many authors put forward the idea that the shielding effect of the user when carrying the PEM involves a non-negligible underestimation of the measurement data [Blas et al, 2007;Knafl et al, 2008;Neubauer et al, 2010;Röösli et al, 2010;Bolte et al, 2011;Rodríguez et al, 2011]. As is the case for all electromagnetic radiation, high frequency electromagnetic fields carry energy, and when the body is exposed to radio waves some of this energy is absorbed [Advisory Group on Non-ionizing Radiation (AGNIR), 2012] or scattered [Thielens et al, 2013], causing the underestimation of the PEMs readings.…”