Receiver coil parameter optimization process for the efficiency of an implantable Inductive Power Transfer system

In order to develop a high power transmission efficiency for an Inductive Power Transfer (IPT) system especially the parameters of the receiver (RX) coil have to be analyzed in detail. This becomes essential, when the RX coil is part of a medical implant and dramatically limited in size. The parameters, which completely describe a coil, are its inductance and ohmic losses. Both values are just dependent on a few geometrical and material parameters, i.e. filling factor, diameter of the wire, outer radius, inner radius and length of the coil, as well as the length and the initial permeability of the utilized ferrite rod. This study shows that, the two latter parameters have both to be maximal to reach the highest efficiency of the system. The effect of the remaining parameters on the system efficiency in a predefined parameter's range can be summarized as follows: optimal points for the inner and outer radius as well as for the length of the coil have been found, while for the filling factor an analytical expression has been found to show that it has to be maximized to get the best efficiency. Finally, the wire diameter that was found to be the most critical parameter can be optimized for a given set of parameters by calculating an optimal value for the ohmic losses of the RX coil.