A consideration of open- and short-end type helical antennas for magnetic-coupled resonant wireless power transfer

Antenna geometry for coupled-resonant wireless power transfer is discussed. We compared open-ended type self-resonant helical antenna and short-ended type capacitor loaded helical antenna from a viewpoint of 1) undesired emission, 2) effect of conductivity, 3) transfer distance, and 4) effect of human body. We have found that short-ended helical antenna has an advantage in low emission, long transfer distance, and low influence of resonant frequency from human body. On the other hands, the open-ended antenna has an advantage in low transmission loss due to a conductivity of wire. This is because both electric-field coupling and magnetic-field coupling are dominant for the open-ended antenna while only magnetic-field coupling is dominant in the short-ended antenna.