Operating frequency selection for loosely coupled wireless power transfer systems with respect to RF emissions and RF exposure requirements

Loosely-coupled (LC) wireless power transfer (WPT) systems based on non-radiative magnetic resonance are finding day to day applications in charging portable consumer electronics. A key design choice is the WPT operating frequency. The frequency range from several kHz to several MHz, but generally below 10 MHz, is of particular interest. In this paper, we discuss the LC WPT operating frequency selection in terms of the existing regulatory framework and requirements for RF emissions and RF exposure. Quantities of interest include freespace electric and magnetic fields, induced electric field, induced current density and specific absorption rate (SAR) in human tissue. We recommend LC WPT to be operated in an ISM band for RF emissions compliance.