Sunohara Tetsu, Hirata Akimasa, Laakso Ilkka, Onishi Teruo
Department of Computer Science and Engineering, Nagoya Institute of Technology, Nagoya, Aichi 466-8555, Japan.
Phys Med Biol. 2014 Jul 21;59(14):3721-35. doi: 10.1088/0031-9155/59/14/3721. Epub 2014 Jun 17.
This study investigates the specific absorption rate (SAR) and the in situ electric field in anatomically based human models for the magnetic field from an inductive wireless power transfer system developed on the basis of the specifications of the wireless power consortium. The transfer system consists of two induction coils covered by magnetic sheets. Both the waiting and charging conditions are considered. The transfer frequency considered in this study is 140 kHz, which is within the range where the magneto-quasi-static approximation is valid. The SAR and in situ electric field in the chest and arm of the models are calculated by numerically solving the scalar potential finite difference equation. The electromagnetic modelling of the coils in the wireless power transfer system is verified by comparing the computed and measured magnetic field distributions. The results indicate that the peak value of the SAR averaged over a 10 g of tissue and that of the in situ electric field are 72 nW kg(-1) and 91 mV m(-1) for a transmitted power of 1 W, Consequently, the maximum allowable transmitted powers satisfying the exposure limits of the SAR (2 W kg(-1)) and the in situ electric field (18.9 V m(-1)) are found to be 28 MW and 43 kW. The computational results show that the in situ electric field in the chest is the most restrictive factor when compliance with the wireless power transfer system is evaluated according to international guidelines.
本研究针对基于无线充电联盟规范开发的感应式无线电力传输系统产生的磁场，在基于人体解剖结构的模型中研究比吸收率（SAR）和原位电场。该传输系统由两个被磁片覆盖的感应线圈组成。研究考虑了等待和充电两种情况。本研究中考虑的传输频率为140kHz，处于磁准静态近似有效的范围内。通过数值求解标量势有限差分方程，计算模型胸部和手臂中的SAR和原位电场。通过比较计算得到的和测量得到的磁场分布，验证了无线电力传输系统中线圈的电磁建模。结果表明，对于1W的发射功率，10g组织平均比吸收率的峰值和原位电场的峰值分别为72nW/kg和91mV/m。因此，满足SAR暴露限值（2W/kg）和原位电场暴露限值（18.9V/m）的最大允许发射功率分别为28MW和43kW。计算结果表明，根据国际准则评估无线电力传输系统的合规性时，胸部的原位电场是最具限制性的因素。
