Printed Spiral Coils for Wireless Power Transfer: Design Guidelines and Characterization

Inductive Wireless power Transfer systems for biomedical implants might benefit from using Printed Spiral Coils on flexible foils. Due to the proximity effect, an optimum pitch and number of turns exists that maximizes the Q factor. Based on quasi-static simulations, design equations for pitch and number of turns are given. For a coil of given outer diameter and for a given distance, the outer diameter of a second coil can be optimized for maximum coupling. Design equations for determining this outer diameter are given. A VNA two-port measurement technique for determining low real impedances of coils has been implemented and successfully validated.