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A formula for the optimal relation between the width of a planar conductor (w0), the total width of parallel straight planar conductors (W), and the number of the parallel conductors (N) for the minimum ohmic resistance is presented. The formula is verified for the frequency range between 2 and 27.12 MHz according to N by using the finite element method. By experimentation, it is also shown that the proposed formula can be applied to design low‐loss circular planar coils. [ABSTRACT FROM AUTHOR]

An effective calculation method for AC resistance and the inductance of planar rectangular spiral coils is proposed. For the calculation, a volume filament model and its equivalent circuit are provided. By using the method, AC resistance and inductance are calculated accurately in megahertz frequency range by including both skin and proximity effects. The method is verified with experiments and used to optimise rectangular spiral coils for the maximum quality factor (Q‐factor) at 6.78 MHz. A small planar rectangular coil is shown to have the maximum Q‐factor when the width of the innermost coil loop is about a half of that of the outermost coil loop. [ABSTRACT FROM AUTHOR]

A planar coil of multiple loops connected in series and in parallel is proposed for wireless power transfer (WPT). The current direction in each loop is mixed in forward and in reverse. The proposed coil gives uniform mutual inductance and enables simple impedance matching for free‐positioning WPT. [ABSTRACT FROM AUTHOR]