Autores
Bahillo A, Blas J, Fernandez P, Mazuelas S, Vinuela A, Lorenzo RM, Abril EJ.  (2008). E-field errors associated with RF dosimeters for RF human exposure assessment in urban environments. Conf  Proc IEEE Eng Med Biol Soc. 2821-2824.

Background
Electromagnetic dosimetry quantifies the interaction of electromagnetic fields with biological tissues and is primarily used for evaluation of human exposures. Current personal dosimeters are measuring devices for free field and are calibrated in free space. Previously, the authors showed that underestimation of the electric field could occur when the meter was located in a shadow region generated by the presence of the human body. In that previous study, only waves with 0 degrees in azimuth were considered. However, because of diffractions and reflections, the radiofrequency (RF) signal at a given location is the sum of various waves with different amplitudes and directions of arrival (DoAs). In this paper, some insights into the potential errors which could be associated with body-worn RF dosimeters in a multi-path scenario, such as the urban environment are presented.

Objective
The goal of the study was to contribute to the assessment of human exposure by analyzing the local interaction behavior of the dosimeter with an anatomical model of the human body, accounting for multiple waves with different amplitudes and directions of arrival. By considering different mean azimuth power distributions, the authors have analyzed the levels of the electric field in the potential position of the body-worn RF dosimeter at GSM-900 band.

Methods
As a first step, the two-dimensional ray-tracing technique was used to evaluate the mean azimuth power distribution of the electric field in urban environment. As a second step, the finite-difference time-domain method was applied in order to study the exposure of an anatomical model of the human body according to the mean azimuth power distribution obtained by the ray-tracing technique.

Results and interpretation
It has been shown that at the potential location of the dosimeter (human back at waist level) the electric field strength is similar for the four mean azimuth power distributions considered in the analysis. It can be inferred from the results that, if a body-worn dosimeter is used for the assessment of personal exposures in epidemiological studies, on average, the dosimeter reading is at least 5 dB lower than the electric field in the absence of the human.

Conclusion
If a personal dosimeter is fixed to the human back at waist level, the dosimeter reading is lower than the electric field strength in the absence of the human, even in a multi-path environment. Understanding and predicting in which way the presence of the human body alter the plane wave propagation is a fundamental aspect when a dosimeter is used for the assessment of personal exposure in an urban environment.

 



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