The Impact of Thermal Modeling on Limiting RF-EMF

Norbert Leitgeb

Institute of Health Care Engineering with European Notified Body of Medical Devices, Graz University of Technology, Graz, Austria..

DOI: 10.4236/jemaa.2013.54022                

Abstract

The paper quantitatively assesses the relationship between specific energy absorption rates (SAR) of radio frequency (RF) electromagnetic fields (EMF) and resulting intracorporal tissue temperature changes (ΔT) at whole body exposure of a small person to resonant RF EMF. Applied thermal modeling allowed accounting also for dynamic thermoregulatory responses. As expected from physical laws the correlation of all local SAR values and ΔT data was fairly good. However, at local level SAR proved to be only weakly associated with ΔT. Even if averaged, over any 10 g tissue the ratio ΔT_10g/SAR_10g still varied by almost two orders of magnitudes. Blood perfusion was found to play a major role in affecting local temperature changes and caused even net cooling. The results demonstrate that local SAR is a poor surrogate for local temperature change, and that conventional static thermal modeling underestimates body core temperature. Results demonstrated that recommended reference levels of RF EMF fail to reliably prevent from exceeding yet legally binding basic restrictions not only with regard to whole-body SAR but also with regard to whole-body temperature rise (ΔT). Consequently, from a legal point of view general presumption of conformity is no longer justified. While thermal basic restrictions were exceeded if related to the whole-body averaged value, compliance could not be excluded with regard to body-core related values. Further results might allow improving EMF limiting in terms of relating it more closely to the basic health-relevant parameter which is tissue temperature change.

Keywords

Electromagnetic Fields; Radio Frequency; Health Risks; Tissue Heating; Specific Absorption Rate

Conflicts of Interest

The authors declare no conflicts of interest.

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