Mechanism for Double-Humped Frequency Characteristics of Whole-Body Average SAR Due to Far-Field Exposure at ICNIRP Reference Level

Electromagnetic absorption of the human body for far-filed exposure at the ICNIRP (International Commission on Non-Ionizing Radiation Protection) reference level shows the double-humped frequency characteristics: the first peak appears at several tens megahertz where whole-body resonance occurs and the second around 2GHz caused by the increase of the reference level. Absorption mechanism at these frequency bands has not yet been revealed sufficiently. Main purpose of this paper is to clarify the difference of absorption mechanism between resonance frequency and GHz bands in comparison of the whole-body average SAR (specific absorption rate) in an anatomically-based model with those in a homogeneous anthropomorphic model and the corresponding cuboid models. We employed a finite- difference time-domain (FDTD) algorithm incorporated with UPML (Uniaxial Perfectly Matched Layer) absorption boundary condition. Computational results exhibited that electromagnetic absorption peak at the resonance frequency band greatly depends on the electric properties of tissue, while the peak at the GHz band is affected by the surface area of the model. We also found that peak whole-body average SAR calculated with a 5-year-child model exceeds the basic limit specified in the public guideline by 23%. Furthermore, the findings obtained here suggest that the cuboid model with carefully-determined dimensions and electrical constants allows us to roughly predict a peak value of whole body average SAR.