SAR variation study from 300 to 5000 MHz for 15 voxel models including different postures

Abstract

An extensive study on specific absorption rate (SAR) covering 720 simulations and 15 voxel models (18–105 kg) has been performed by applying the parallel finite-difference time-domain method. High-resolution whole-body models have been irradiated with plane waves from 300 MHz to 5 GHz by applying various incoming directions and polarizations. Detailed results of whole-body SAR and peak 10 g SAR are reported, and SAR variation in the dB scale is examined. For an adult, the effect of incoming direction on whole-body SAR is larger in the GHz range than at around 300–450 MHz, and the effect is stronger with vertical polarization. For a child (height ∼1.2 m), the effect of incoming direction is similar as for an adult, except at 300 MHz for horizontal polarization. The effect of the phantom (18–105 kg) on whole-body SAR is larger at around 2–5 GHz and at vertical 300 MHz (proximity of whole-body resonance for the child) than at around horizontal 300–900 MHz. Body posture has little effect on whole-body SAR in the GHz range, but at around 300–450 MHz, one may even expect a 2 dB rise in whole-body SAR if posture is changed from the standing position. Posture affects peak 10 g SAR much more than whole-body SAR. The polarization of the incident electric field may have an effect of several dB on whole-body SAR. Between 2 and 5 GHz for adults, whole-body SAR is higher for horizontal than for vertical polarization, if the incoming direction is in the azimuth plane. In the GHz range, horizontal polarization gives higher whole-body SAR, especially for irradiation from the lateral direction. A comparison between homogeneous and heterogeneous models was done. A homogenized model underestimates whole-body SAR, especially at ∼2 GHz. The basic restriction of whole-body SAR, set by ICNIRP, is exceeded in the smallest models (∼20 kg) at the reference level of exposure, but also some adult phantoms are close to the limit. The peak 10 g SAR limits were never exceeded in the studied cases. The present ICNIRP guidelines should be revised by lowering the reference levels, especially at around 2–5 GHz.