Rodríguez Begoña, Blas Juan, Lorenzo Rubén M, Fernández Patricia, Abril Evaristo J
Center for the Development of Telecommunications of Castilla y León CEDETEL, Boecillo, Valladolid, Spain.
Bioelectromagnetics. 2011 Apr;32(3):209-17. doi: 10.1002/bem.20627. Epub 2010 Nov 30.
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.
个人暴露计（PEM）通常用于评估射频电场或磁场的暴露情况。然而，其读数容易受到人体存在所引起的场扰动相关误差的影响。本文提出了一种用于表征这种效应的新颖分析方法。利用射线追踪技术，对有无这种阴影效应近似情况下的PEM测量进行了模拟。特别地，由于全球移动通信系统（GSM）手机频段的普遍性，我们选择了该频段，具体而言，我们考虑了受试者在相对开阔区域户外行走的情况。这些模拟结果与在35分钟步行过程中的实际PEM测量结果进行了对比。结果表明，在均方根误差和电场累积分布函数（CDF）方面具有良好的一致性，考虑阴影效应时会有显著改善。特别是，在考虑阴影效应时，柯尔莫哥洛夫-斯米尔诺夫（KS）检验给出的P值为0.05，而忽略这种效应时P值为10⁻¹⁴。此外，虽然已发现无人体时的电场水平遵循 Nakagami 分布，但对数正态分布比 Nakagami 分布更能拟合PEM值的统计数据。总之，虽然可以通过使用校正因子来调整均值，但由于阴影效应，CDF中还存在其他需要特别关注的变化，因为它们可能导致系统误差。
