Some basic Q & A on wireless power transfer

This paper presents some questions and answers on the wireless power transfer. Firstly, it investigates the physical limitation of a wireless power transfer using spherical modes. It is found that there is a limitation on the transfer efficiency depending on the distance between the resonators and efficiency of antennas. Secondly, we compare the performance of WPTS with respect to the source type. In addition, a method is suggested for efficient WPT when the distance between antennas is varied. Thirdly, a time division method is suggested for WPTS to charge multiple receivers. Finally, we present an analytic formula which can be used to differentiate Inductive Coupling and Magnetic Resonance Coupling which are ambiguously used in wireless power transfer system.