Temperature Rise for Brief Radio-Frequency Exposure Below 6 GHz

In international guidelines for human protection from radio-frequency (RF) electromagnetic fields, the specific absorption rate (SAR) averaged over 6 minutes and 10 g of tissue is used as a physical quantity to prevent excess local temperature rise. The resultant SAR restriction has been set to avoid potential adverse health effects due to the temperature elevation resulting from RF energy absorption. In the public consultation version of the upcoming ICNIRP RF guidelines (10th July, 2018), a specific absorption (SA) limit was set to avoid heating from brief exposures (shorter than 6 min). However, to the best of our knowledge, no prior research has evaluated the temperature rise for single/multiple pulses with energy equivalent to the 6 min exposure SAR restriction for continuous waves. This study computed the temperature rise for brief pulse exposures based on bioheat computations. We first confirmed that the peak temperature rise for a pulse with SA corresponding to occupational exposure exceeds the steady-state temperature rise for temporally uniform continuous wave exposure. We then proposed the SA limit from a regression curve that is dependent on the duration of brief exposure to RF pulse(s). The temperature rise in a multilayer cube and an anatomical human model were also computed for exposures to multiple pulses. The temperature rise from multiple pulses satisfying the formula was found to be below the relevant threshold level. The SA based on this regression curve can be used as a metric to prevent excess temperature rise for different brief exposure scenarios below 6 min.