Which way for wireless power: High Q or high k?

Abstract

The current popular technical paradigm insists high resonator quality factor Q, and by implication high frequency operation, is essential for efficient power transmission by means of resonant induction. This paper examines the theoretical argument and the experimental evidence against the current paradigm. It shows high frequency operation has few, if any, operational advantages and indeed has several significant disadvantages. Instead the paper makes the case that the path forward for efficient and inexpensive resonant induction wireless power should be based upon maximizing the transfer coil pair coupling coefficient k, rather than Q, in combination with a relatively low operating frequency. Data from a number of independent researchers as well as the work of Momentum Dynamics point to the need for same-size couplers. The advantages include reduced eddy current heating of vehicle structures, better misalignment tolerance, reduced flux density, higher overall power transfer efficiency, and reduced stray magnetic field emissions. The mathematical basis for preferring lower Q and higher coupling will be explained.