A consideration of electric and magnetic coupling coefficient of spiral antenna for wireless power transfer

Wireless power transfer technologies are now getting large interests. Coupled resonant wireless power transfer proposed by MIT has an advantage of high efficiency and middle range transfer distance. For a practical use, design criteria of high efficiency antennas should be established. We have investigated open-end and short-end helical antennas. Recently, it has been found that coupling between transmitting and receiving antennas become stronger by arranging spiral antennas in reverse direction. In this report, open-end and short-end spiral antennas with normal and reverse arrangement are investigated from the viewpoints of coupling coefficient and transmission efficiency. We have found that transmission distance is improved by arranging antenna in reverse direction. Effect of reverse arrangement of the open-end model is larger than the short-end model because both electric and magnetic fields are dominant in the open-end model.