The field of wireless power transfer (WPT) is very old,
dating back to Faraday’s discovery of magnetic induction in
1831 and Hertz’s demonstration of electromagnetic wave
propagation in 1887 [1]. Tesla experimented with large
scale wireless power distribution in the early 1900s [2]. Because
of continuing demand for practical WPT systems, the
field remains active with many recent examples of wireless
power transfer systems employing near-field inductive
(magnetic) or electric field coupling, including commonly
used inductive toothbrush chargers and proximity
type RFID tags [3], as well as research systems capable