Optimization of Resonant Inductive Wireless Power Transfer Using Multilayer Flat Spiral Coils

A method of using loading capacitors of varying sizes to experimentally determine the alternating current behavior of resistance and inductance for a multilayer flat spiral coil is presented. For the presented coil design, the Dowell method is shown to underpredict the alternating current resistance of the coil by as much as a factor of 4 for frequencies up to 10 kHz. A classical modification to the Dowell method produces improved results but still underpredicts the alternating current resistance by as much as a factor of 2. Curve fits of the form used in Dowell’s method are applied to experimentally obtained data, allowing for the identification of the frequency at which wireless power transfer efficiency is maximized. In addition, an analytical approach to predicting coil impedance vs the duty cycle of a rectangular wave applied voltage is presented and is shown to agree well with experimentally obtained results.