Nowadays, the establishment of the technologies of contactless power transfer (CPT) for electric vehicles (EVs) are needed. The system can provide people with a convenient charging system which can powers their EVs wirelessly and automatically when they park. Traditional CPT solutions have the problem of distance between transmitting antennas and receiving antennas (air gap), as well as from the misalignment of the antennas. Those systems cannot power at a great distance and the efficiency is very low. In this paper, CPT by magnetic resonance couplings and small antennas are proposed. These techniques more easily span air gaps and are more forgiving to antennas misalignments than traditional solutions. The Efficiencies are still high when the air gaps are longer than the diameter of the antennas. As well, the efficiencies are over 90% when the antennas are half a diameter out of alignment. For example, when the air gap and the displacement is 150mm, the efficiency is about 96%. The magnetic resonant couplings can power wirelessly even if there is a weak connection. Thus, a large air gaps with high efficiency are possible. The relation between two resonant frequencies and the coupling coefficient are described using the method of equivalent circuits. As well, the relation between resonant frequencies and the efficiencies, especially the moment of decreasing, are described.
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