Department of Radio Science and Engineering, Helsinki University of Technology, Otakaari 5A, 02150 Espoo, Finland.
Phys Med Biol. 2010 Feb 21;55(4):1157-76. doi: 10.1088/0031-9155/55/4/017. Epub 2010 Jan 28.
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 approximately 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 approximately 2 GHz. The basic restriction of whole-body SAR, set by ICNIRP, is exceeded in the smallest models ( approximately 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.
已应用并行有限差分时域方法对特定吸收率 (SAR) 进行了涵盖 720 次模拟和 15 个体积模型 (18-105kg) 的广泛研究。通过应用各种入射方向和极化，用平面波对高分辨率全身模型进行了照射。报告了全身 SAR 和峰值 10gSAR 的详细结果，并检查了 SAR 在分贝刻度上的变化。对于成年人，在 GHz 范围内，入射方向对全身 SAR 的影响比在 300-450MHz 左右时更大，垂直极化的影响更强。对于儿童(身高约 1.2m)，入射方向的影响与成年人相似，除了 300MHz 时的水平极化。对于 18-105kg 的人体模型，在 2-5GHz 和垂直 300MHz(儿童全身共振的接近)时，对全身 SAR 的影响比在 300-900MHz 左右时更大。在 GHz 范围内，人体姿势对全身 SAR 的影响很小，但在 300-450MHz 左右，如果人体姿势从站立位置改变，全身 SAR 甚至可能增加 2dB。姿势对峰值 10gSAR 的影响比全身 SAR 大得多。入射电场的极化可能对全身 SAR 有几个 dB 的影响。对于成年人，在 2-5GHz 之间，如果入射方向在方位平面内，水平极化的全身 SAR 高于垂直极化。在 GHz 范围内，水平极化会产生更高的全身 SAR，尤其是从侧面照射时。对均匀和非均匀模型进行了比较。均匀模型低估了全身 SAR，尤其是在大约 2GHz 时。在参考暴露水平下，最小模型(约 20kg)超过了 ICNIRP 设定的全身 SAR 基本限制，但一些成年人体模型也接近限制。在所研究的情况下，峰值 10gSAR 限制从未被超过。目前的 ICNIRP 指南应通过降低参考水平进行修订，特别是在 2-5GHz 左右。
