Compliance Testing Methodology for Wireless Power Transfer Systems

Wireless power transfer (WPT) systems have become popular, with applications in charging portable electronics via inductive coupling between a transmit and receive coil. Accurate estimation of the induced exposure is required as the incident magnetic fields near the coils often exceed the reference levels. Standardized procedures do not yet exist for the demonstration of compliance of these products with electromagnetic guidelines for human exposure. For this purpose, we propose a conservative methodology using simplified homogeneous phantoms. An approximation for the minimum compliance distance for user exposure is developed based on the theoretical evaluation of the induced fields and simulations of detailed anatomical models. The simulation results are experimentally validated for a practical WPT application at 6.78 MHz. Criteria for exclusion of WPT systems from compliance evaluation are presented as a function of coil dimensions, operating current and frequency.