Analysis of the multi-layer Printed Spiral Coil for wireless power transfer system used in medical implants

The performance of the wireless power transfer (WPT) system is highly constrained by the coils in the coupling field. The coils can be fabricated as multi-layer Printed Spiral Coil (PSC) due to the development of the Printed Circuit Board (PCB) technique. This spatial effective coil implements the miniaturization for medical implants with higher inductance and lower resonance frequency. The accurate design of the PSC will be extremely complex with the analytical derivation based on Maxwell's equations. In this work, we proposed a new formula to connect the geometrical parameters with the self-resonance frequency and the Q-factor of the PSC. The numerical and experimental method are used to analysis the factors in our formula. We find that the resonance frequency is very sensitive to the number of turns and layers in the PSC. This mathematical method provides a more accurate approach for the coil design and optimization.