This paper describes a size and tissue absorption based comprehensive approach to optimize a pair of coils for the purpose of wireless powering of brain implanted sensors. In the first step, the optimum transmission frequency is determined by considering tolerable coil size, power transmission efficiency and tissue absorption effects. After modeling the important quantities at the frequency of interest, a numerical analysis is performed, revealing a set of coils suitable for efficient inductive powering. This numerical analysis was verified by both FEM simulation and concluding measurements.
All simulations account for the layered structure of the human head, modeling the dielectric properties with Cole-Cole dispersion effects. Furthermore, a strategy of boosting power transmission efficiency is covered in simulation and measurement, particularly the application of a ferrite shielding to the transmission coil. In consequence, a link efficiency of 80% at a coil separation distance of 5mm and 20% at 20 mm using a 10mm planar receiving coil can be achieved, contributing to a higher integration density of multi-channel brain implanted sensors.