Esra Neufeld and Niels Kuster, Health Physics, Early View, online 21 September 2018, doi: 10.1097/HP.0000000000000930
Very broadband wireless devices (bandwidth >1 GHz) operating at frequencies >10 GHz may transmit data in bursts of a few milliseconds to seconds. Even though the time- and area-averaged power-density values remain within the acceptable safety limits for continuous exposure, these bursts may lead to short temperature spikes in the skin of exposed people. In this paper, a novel analytical approach to pulsed heating is developed and applied to assess the temperature-enhancement and -oscillation magnitude relative to continuous exposure as a function of the pulse fraction, which is related to the peak-to-average (PAR) exposure ratio. This has been analyzed for the published perfusion- and diffusion-related thermal time constants observed for plane wave and localized exposures. To manage peak temperatures that considerably exceed an increase of 1 K, the CEM43 tissue damage model, which has a threshold of 600 min (CEM43 dose) for human skin damage based on experimental data, was used to allow large temperature oscillations that remain below the level at which tissue damage occurs. To stay consistent with current safety guidelines, safety factors of 10 for occupational exposure and of 50 for the general public were integrated into the model. The assumptions and limitations of the new approach, such as the thermal- and tissue-damage-models employed, homogeneous skin, and consideration of localized exposure by means of a modified time-constant, are discussed in detail.
The scientific and technical impact of the study can be summarized as: