Findlay R P, Dimbylow P J
National Radiological Protection Board, Chilton, Didcot, Oxon OX11 0RQ, UK.
Phys Med Biol. 2005 Aug 21;50(16):3825-35. doi: 10.1088/0031-9155/50/16/011. Epub 2005 Jul 28.
A change in the posture of the human body can significantly affect the way in which it absorbs radiofrequency electromagnetic radiation. To study this, an anatomically realistic model of the body has been modified to develop new voxel models in postures other than the standard standing position with arms to the side. These postures were sitting, arms stretched out horizontally to the side and vertically above the head. Finite-difference time-domain (FDTD) calculations of the whole-body averaged specific energy absorption rate (SAR) have been performed from 10 MHz to 300 MHz at a resolution of 4 mm. Calculations show that the effect of a raised arm above the head posture was to increase the value of the whole-body averaged SAR at resonance by up to 35% when compared to the standard, arms by the side position. SAR values, both whole-body averaged and localized in the ankle, were used to derive the external electric field values required to produce the SAR basic restrictions of the ICNIRP guidelines. It was found that, in certain postures, external electric field reference levels alone would not provide a conservative estimate of localized SAR exposure and it would be necessary to invoke secondary reference levels on limb currents to provide compliance with restrictions.
人体姿势的改变会显著影响其吸收射频电磁辐射的方式。为了对此进行研究，已对逼真的人体解剖模型进行修改，以开发出除双臂垂于身体两侧的标准站立姿势之外的其他姿势下的新体素模型。这些姿势包括坐姿、双臂向身体两侧水平伸展以及双臂举过头顶垂直伸展。已在10 MHz至300 MHz频率范围内，以4 mm的分辨率对全身平均比吸收率（SAR）进行了时域有限差分（FDTD）计算。计算结果表明，与双臂垂于身体两侧的标准姿势相比，双臂举过头顶的姿势会使共振时的全身平均SAR值增加高达35%。全身平均SAR值以及脚踝局部的SAR值被用于推导产生国际非电离辐射防护委员会（ICNIRP）指南中SAR基本限制所需的外部电场值。研究发现，在某些姿势下，仅靠外部电场参考水平并不能对局部SAR暴露提供保守估计，因此有必要引入关于肢体电流的二级参考水平，以确保符合限制要求。
