Impedance Matching using Folded Spiral Antenna for Coupled-resonant Wireless Power Transfer

Folded spiral antenna for wireless power transfer (WPT) is prosed. In order to realize maximum available efficiency, impedance matching should be achieved. It is known that the folded dipole antennas has a capability of adjusting input impedance by using two conductors with different diameters. The folded spiral antenna proposed in this report is based on self-resonant spiral antenna, that has folded structure with different diameter conductors. By using the proposed structure, maximum available efficiency is achieved without using a matching circuit. Numerical simulation demonstrates that by using the proposed structure, transfer distance over 80% efficiency extends 3.3 times.