I. Introduction
Recently, demands on autonomous mobile devices, such as smart phones and tablet PCs, have drastically risen. In addition, electric vehicles have been the most important research topic, because fossil fuel is being depleted. Producers are trying to build them with more and more functions, and this causes many problems on providing durable power sources. In order to retain the durable power sources, many researchers have studied and designed magnetic resonators for wireless energy transfer based on experiments, and the electronic circuit analysis [1]; however, its efficiency is still low.