Increasing the radiation efficiency and resistance of electrically small spherical helical antenna for wireless power transfer

The performance of wireless power transfer system depends highly on antenna radiation efficiency, according to the theory. Practical problem of power transfer between electrically small antennas is their impedance match to standard transmission lines. This paper shows how the maximum power transfer efficiency can be reached with new design approach at 10 MHz. Various helical antenna designs are investigated and compared. A combination of two methods is proposed for increasing the radiation efficiency and the input resistance of spherical helical antenna. The results show that it is possible to achieve significantly higher power transfer efficiency at 10 MHz than in the reported literature. The wireless power transfer system consisted of two four-arm spherical helical antennas with k_resa = 0.064, can achieve maximum power transfer efficiency of 95 percent at 2 m.