Design of a Transmitting Coil for Effective Charging Area Expansion Using a Stepped Helical Coil

In this paper, a novel stepped helical coil is proposed with uniform magnetic field generation for effective wireless charging region expansion. The stepped helical coil uses two or more helical coils, and the desired magnetic field can be formed by controlling the number of turns and the diameter of each coil. In addition, this structure is insensitive to the influence of the ground plane and is easy to manufacture due to its simple architecture. The proposed stepped helical coil was tested for its performance by constructing a magnetic resonance 100 W class wireless charging system at a frequency of 140 kHz. The measurement results show that the charging area of 380.1 cm2(71.6%), which maintains 60% efficiency, is about 4 times larger than that of the conventional single helical coil structure.