A Flexible Thin-Film Inductor for High-Efficiency Wireless Power Transfer

Abstract

The design of a thin-film spiral inductor with multi-fin structure on a flexible substrate is proposed that can be used in a fully integrated wireless power transfer (WPT) system. A solid coil with the same dimension and copper thickness but without the multi-fin structure is designed and compared. For the multi-fin coil, the parasitic resistance is reduced from <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$11.6~\Omega $ </tex-math></inline-formula> to <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$5.6~\Omega $ </tex-math></inline-formula> , and the quality factor is increased from 29.9 to 59.6, compared to the solid coil. The multi-fin coil achieves a peak quality factor of 59.6 at 88.2 MHz. Measurement results of an inductive link using the multi-fin receiving coil and a conventional flexible printed circuit transmitting coil demonstrate peak WPT efficiency of 63.7% and 30.5% over a distance of 10 and 25 mm, respectively.