The dominant effect of human exposures to microwaves is caused by temperature elevation ('thermal effect'). In the safety guidelines/standards, the specific absorption rate averaged over a specific volume is used as a metric for human protection from localized exposure. Further investigation on the use of this metric is required, especially in terms of thermophysiology. The World Health Organization (2006 RF research agenda) has given high priority to research into the extent and consequences of microwave-induced temperature elevation in children. In this study, an electromagnetic-thermal computational code was developed to model electromagnetic power absorption and resulting temperature elevation leading to changes in active blood flow in response to localized 1.457 GHz exposure in rat heads. Both juvenile (4 week old) and young adult (8 week old) rats were considered. The computational code was validated against measurements for 4 and 8 week old rats. Our computational results suggest that the blood flow rate depends on both brain and core temperature elevations. No significant difference was observed between thermophysiological responses in 4 and 8 week old rats under these exposure conditions. The computational model developed herein is thus applicable to set exposure conditions for rats in laboratory investigations, as well as in planning treatment protocols in the thermal therapy.
The present study investigates the correlation between maximum temperature elevation and peak massaveraged specific absorption rates (SARs) in layered onedimensional model and layered cubical model. The resolution of the model is 0.5 mm or less in order to calculate the correlation in frequencies up to 10 GHz. Our computational investigation in the one-dimensional model showed that the variability due to the thickness is several dozen percents or more, which is dependent on the frequency. In the three-dimensional homogeneous model, SARs averaged over 10 g provides reasonable correlation with maximum temperature elevation for frequencies up to 6 GHz. For the layered cubical model, the SAR averaged over 1g provides better frequency characteristics of the correlation with the maximum temperature elevation, while the variability of the ratio for different tissue thickness remains future work.
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