Stable and high-efficiency transmission performance is of great significance for wireless power transfer (WPT) system. Despite of some approaches, such as improving the quality factor (Q), regulating current distribution and achieving the impedance matching, can minimize the unfavorable influence and improve the system performance, the uniformity of electromagnetic field need further consideration. This paper proposes a modified tri-axil circular Helmholtz coil (MTHC) to shape the homogeneous magnetic field so as to improve the flexibility of receiving coil position. Compared to a traditional Helmholtz coil, a pair of compensating coil is added in each dimension to generate the extra magnetic field. In addition, various coil parameters are optimized to obtain the larger uniform region and compact structure. To validate the advantage of the proposed coil, a set of theoretical calculations and simulation experiments have been carried.
 

Helmholtz,compensating coil,uniform magnetic field,power efficiency,wireless power transfer