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Megahertz-range wireless power transfer has become a promising approach for increasing spatial freedom of charging. This paper proposes a cylindrical-shaped coil, which can produce the homogeneous magnetic field in a plane. The coil consists of two helical windings, which are wound to guide the current in opposite directions. A single power source is used to excite the transmitter without any current amplitude or phase control circuits. Furthermore, since the parasitic capacitance of the coil is not negligible due to the complexity of the coil shape, we develop a general equivalent model with parasitic capacitance for the analysis of complex coils. The system efficiency of the proposed omnidirectional wireless power transfer device is validated by a practical experiment. The measured DC-to-DC efficiency of approximately 72.4% and the load power of 13 W are demonstrated for the proposed wireless charging system at 6.78 MHz operating frequency. Finally, we verify that the electromagnetic exposure satisfies the safety regulations.

Original languageEnglish
Pages (from-to)10045-10054
Number of pages10
JournalIEEE Transactions on Industrial Electronics
Issue number10
Early online date2022
Publication statusPublished - Oct 2022
MoE publication typeA1 Journal article-refereed


  • Cylindrical transmitting coil
  • omnidirec-tional
  • specific absorption rate (SAR)
  • wireless power transfer (WPT)


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