Xi Jingtian, Christ Andreas, Kuster Niels
Foundation for Research on Information Technologies in Society, Zurich, Switzerland.
Department of Information Technology and Electrical Engineering, Swiss Federal Institute of Technology, Zurich, Switzerland.
Phys Med Biol. 2023 Jan 20;68(3). doi: 10.1088/1361-6560/aca875.
. Regulators require that wireless power transfer (WPT) systems and other strong magnetic field sources are compliant with the basic restrictions (BR) defined as the limits of the fields induced in the human body, i.e. the induced electric field/current density/specific absorption rate limits. This can be achieved by demonstrating compliance with the reference levels (RL) defined in air without the human body, i.e. the incident electric/magnetic field limits. Local sources, such as WPT transmitters, generate non-uniform fields that can locally exceed the RL while the induced fields are still well below the BR. In these cases, robust compliance with BR can be demonstrated, generally requiring a large number of simulations. In this study, we proposed an efficient evaluation using a homogeneous phantom and applying a coverage factor to account for the local field enhancements caused by the dielectric contrasts of the highly inhomogeneous human tissues.. The generally applicable coverage factors were derived from a statistical analysis of the field enhancements observed on four magnetic near-field sources placed at different separation distances (2-80 mm) and locations on the back of 12 anatomical models. The field enhancements were characterized by the ratios between the peak induced fields in the anatomical models and those in the homogeneous half-space phantom (= 55,= 0.75 S m,= 1,000 kg m) at the same distance.. The resulting 99th percentile coverage factors range from 1 and 9 depending on the dosimetric quantity.. The use of these coverage factors reduces the compliance testing effort from hundreds of simulations to only one, and makes experimental testing feasible without the support of simulations. The study also demonstrates that running only a few use-case simulations with anatomical models may underestimate the exposure by more than 10 dB.
监管机构要求无线电力传输（WPT）系统和其他强磁场源符合基本限制（BR），该限制定义为人体中感应场的限值，即感应电场/电流密度/比吸收率限值。这可以通过证明符合在无人体的空气中定义的参考水平（RL）来实现，即入射电场/磁场限值。诸如WPT发射器之类的局部源会产生不均匀的场，这些场在局部可能会超过RL，而感应场仍远低于BR。在这些情况下，可以证明能稳健地符合BR，通常需要进行大量模拟。在本研究中，我们提出了一种高效的评估方法，使用均匀人体模型并应用覆盖因子来考虑由高度不均匀的人体组织的介电对比度引起的局部场增强。通用的覆盖因子是通过对放置在12个解剖模型背部不同分离距离（2 - 80毫米）和位置的四个磁近场源上观察到的场增强进行统计分析得出的。场增强通过解剖模型中的峰值感应场与在相同距离处均匀半空间人体模型（= 55，= 0.75 S m，= 1,000 kg m）中的峰值感应场之比来表征。根据剂量学量的不同，所得的第99百分位数覆盖因子范围为1至9。使用这些覆盖因子可将合规性测试工作量从数百次模拟减少到仅一次，并使在无需模拟支持的情况下进行实验测试成为可能。该研究还表明，仅对解剖模型运行少数用例模拟可能会使暴露估计值低估超过10 dB。
