Improvements in performance of resonant coils are important for the range and efficiency of wireless power transfer (WPT); however, these improvements are difficult to measure using the conventional figure-of-merit (FoM), which is the product of quality factor and coupling factor.
In this paper, we proposed a new FoM that is an indication of the performance of a WPT coil technology independent of a specific implementation, and can be calculated using commonly reported parameters: coil diameter, transmission range, and coil-to-coil efficiency.
The new FoM is the ratio of the loss fraction of a reference system and and the system-under-test. The reference system models two-loops of solid wire that are scaled to the same overall size as the system-under-test. We computed the FoM for a few WPT systems in the literature, and found the highest FoM to be 3.4, achieved using a self-resonant structure.