SAR versus S_inc: What is the appropriate RF exposure metric in the range 1–10 GHz? Part I: Using planar body models

Abstract

This is the first of two articles addressing the most appropriate crossover frequency at which incident power flux density (S(inc)) replaces the spatial peak value of the specific energy absorption rate (SAR) averaged over 1 or 10 g (i.e., peak 1 or 10 g SAR) as the basic restriction for protecting against radiofrequency (RF) heating effects in the 1-10 GHz range. Our general approach has been to compare the degree of correlation between these basic restrictions and the peak induced tissue temperature rise (DeltaT) for a representative range of population/exposure scenarios. In this article we particularly address the effect of human population diversity in the thickness of body tissue layers at eight different sites of the body. We used a Monte Carlo approach to specify 32000 models (400 models for each of 8 body sites for 10 frequencies) which were representative of tissue thicknesses for age (18-74 years) and sex at the eight body sites. Histogram distributions of S(inc) and peak 1 and 10 g SAR corresponding to a peak 1 degrees C temperature rise were obtained from RF and thermal analyses of 1D multiplanar models exposed to a normally incident plane wave ranging from 1 to 10 GHz in thermo-neutral environmental conditions. Examination of the distribution spread of the histograms indicated that peak SAR was a better predictor of peak tissue temperature rise across the entire 1-10 GHz frequency range than S(inc), as indicated by the smaller spread in its histogram distributions, and that peak 10 g SAR was a slightly better predictor than peak 1 g SAR. However, this result must be weighed against partly conflicting indications from complex body modeling in the second article of this series, which incorporates near-field effects and the influence of complex body geometries.

Tissue models for RF exposure evaluation at frequencies above 6 GHz

“…A particularly complete reference on the physical properties of the skin is the “Report of the Task Group on Reference Man” [Snyder et al, ]. Variations in thickness of skin and subcutaneous fat have been reviewed from the perspective of microwave dosimetry by Anderson et al [].…”

Analysis of ICNIRP 2020 Basic Restrictions for Localized Radiofrequency Exposure in the Frequency Range above 6 GHz

“…For all temperature-rise computations, a convective surface with a heat loss coefficient of h = 10 W m −2 o C −1 was adopted. This value or ones close to it were used in a number of studies (Anderson et al 2010; Sasaki et al 2017; Morimoto et al 2017).…”

Lessons and Perspectives from a 25-Year Bioelectromagnetics Research Program

“…Much effort has focused on determining the appropriate metrics for assessing localized RF exposure over the frequency range 1–10 GHz [39,40,41]. Our findings have been used by international standards-setting bodies and regulators to clarify whether the current metrics are appropriate or whether they should be modified.…”