Conditions of maximum efficiency for wireless power transfer between two helical wires

The effects of loading and transmission distance on the efficiency and the input impedance of a wireless power transfer system composed of two helical wire antennas are investigated in detail. These antennas operate in their non-radiative near-field region. The method of moments (MoM) full-wave simulation in FEldberechnung bei Körpern mit beliebiger Oberfläche (FEKO) is used to determine current distribution on this wire structure. The conditions of maximum efficiency for mid-range (0.1̈) wireless power transfer are studied for various load resistances. It is found that the wireless power transfer efficiency is a maximum for the values of the load resistance in the range of 330̈400̈̈, for transmission distances up to 3.3 times the transmitter size with a base radius of 0.01̈. To improve the power transmission efficiency, a ̈repeater̈ helical structure is introduced. This helical structure improves the efficiency up to 35̈ in a transmission distance of 0.1̈.