High-Q flexible spiral inductive coils

A limitation on the optimal design of inductive coils for wireless power transfer is its physical size. We investigated the effect of varying width and spacing of conductive trace of spiral inductive coils in order to improve its quality factor and hence power transfer efficiency between two coils. These spiral coils have inner and outer diameter of 23 mm and 36.5 mm, respectively. We found that for the same number of turns, quality factor Q increases with an increase in spacing. This is attributed to proximity effects in adjacent conductive tracks of the coil. An increase of Q at 6.78 MHz by 121% from the minimum value was achieved by systematically varying the different topologies. We conclude that an optimal topology of choice for a spiral coil is larger spacing and smaller number of turns.