Efficient Tier 4 Compliance Evaluation of Inductive WPT Systems

Wireless power transfer systems require demonstration of compliance with the basic restrictions (induced electric field/current density/specific absorption rate) as the reference levels (incident electric/magnetic fields) largely overestimate human exposure in the close near field of the magnetic field sources and are therefore too conservative. Though the field-body interaction is dominated by the eddy current induced in the lossy tissues, the dielectric contrasts of the highly inhomogeneous tissues can lead to a strong local enhancement of the induced electric field. Therefore, a robust compliance testing of any source would require hundreds of simulations exposing various anatomical models at different positions covering all use cases to determine the maximum induced fields. In this study, we determined generally applicable coverage factors for the induced electric field when compared to the result in a standardized homogeneous half-space phantom $(\epsilon_{r}=55, \sigma=0.75\text{S}/\text{m}, \rho=1000\text{k}\text{g}/\text{m}^{3})$ at the same distance. Four magnetic field sources placed at different separation distances (2-80 mm) and different locations at the back of 12 Virtual Population anatomical models were considered. The coverage factor (99
^th
percentile) for $2\times 2\times 2\text{m}\text{m}^{3}$-cube-averaged induced electric field derived from this study is 9.0. By applying the coverage factors, the compliance testing effort is reduced from hundreds of simulations to only one.