SAR versus S(inc): What is the appropriate RF exposure metric in the range 1-10 GHz? Part II: Using complex human body models.

This is the second of the two articles that present modeling data and reasoned arguments for specifying the appropriate crossover frequency at which incident power flux density (S(inc)) replaces the peak 10 g averaged value of the specific energy absorption rate (SAR) as the designated basic restriction for protecting against radiofrequency electromagnetic heating effects in the 1-10 GHz range. In our first study, we compared the degree of correlation between these basic restrictions and the peak-induced tissue temperature rise (DeltaT) for a representative range of population/exposure scenarios using simple multi-planar models exposed to plane wave conditions. In this complementary study, complex heterogeneous head models for an adult and 12-year-old child were analyzed at 1, 3, 6, 8, and 10 GHz for a variety of exposure conditions. The complex models indicate that peak DeltaT is better correlated with peak 10 g SAR than S(inc) at 1 and 3 GHz and with S(inc) at 6-10 GHz, in contrast to the results from Part I. Considering the planar and complex body modeling results together, and given the equivocal indications of the two metrics in the 6-10 GHz range, we recommend that the breakpoint be set at 6 GHz. This choice is also based on other considerations such as ease of assessment. We also recommend that the limit level of S(inc) should be adjusted to provide a better match with 10 g SAR in the induced tissue temperature rise.