A Spiral Resonators Passive Array for Inductive Wireless Power Transfer Applications with Low Exposure to near Electric Field

In this article, we demonstrate the near electric field reduction ability of spiral resonators arrays (SRAs) in resonant inductive wireless power transfer (WPT) applications. In particular, we show that a suitably designed planar SRA, placed in the proximity of the driver loop, can significantly decrease the electric field level at the operative frequency, thus reducing the potentially dangerous radiation (i.e., the specific absorption rate) in the case of human exposure. In addition, due to the thin structure of the SRAs, the system is able to enhance the performance with respect to a conventional simple driver-receiver system for a fixed working distance. A systematic study has been performed through electromagnetic simulations to evaluate the optimum number of array unit cells to eventually achieve a compromise between efficiency enhancement and electric field shielding on a two-coil system, selected as a test case. Finally, the numerical results have been confirmed through measurements conducted on fabricated prototypes of the proposed WPT configurations. The introduced solution can be remarkably useful in all the WPT applications requiring a close interaction with human operators where exposure is a concern, such as automotive applications, biomedical implants, and rechargeable devices.