Esra Neufeld, Eduardo Carrasco, Manuel Murbach, Quirino Balzano, Andreas Christ, and Niels Kuster, Bioelectromagnetics December 2018, Volume 39, Issue 8, pp. 617–630; online 01 November 2018; doi: https://doi.org/10.1002/bem.22147
The objective of this paper is to determine a maximum averaging area for power density (PD) that limits the maximum temperature increase to a given threshold for frequencies >6 GHz. This maximum area should be conservative for any transmitter at any distance >2 mm from the primary transmitting antennas or secondary field-generating sources. To derive a generically valid maximum averaging area, an analytical approximation for the peak temperature increase caused by localized exposure has been developed. The results for a threshold value for the temperature increase of 1 K have been validated against simulations of a series of sources composed of electrical and magnetic elements (dipoles, slots, patches, and arrays) that represent the spectrum of relevant transmitters. The validation was successful for frequencies at which power deposition occurs superficially, i.e., at >10 GHz. In conclusion, the averaging area for a PD limit of 10 W/m2 that conservatively limits the temperature increase in the skin to less than 1 K at any distance >2 mm from the transmitters is frequency dependent, increases with distance, and ranges from 3 cm2 at <10 GHz to 1.9 cm2 at 100 GHz. In the far-field, the area depends additionally on distance and the antenna array aperture. The correlation was found to be worse at frequencies <10 GHz and very close to the source, the systematic evaluation of which is part of another study on the ratio of temperature increase to incident power density to investigate the effect of different coupling mechanisms in the reactive near-field. The model presented herein can be applied directly to all other PD and temperature thresholds.
The scientific and technical impact of the study can be summarized as: