An efficient inductive power link design for retinal prosthesis

This paper presents the design of a highly efficient power link based on class-E driven, inductively coupled coil pair. An optimal power link design for retinal prosthesis and other implants must take into consideration the allowable electric and magnetic field safety limits, which in turn govern the inductances of the primary and secondary coils. In retinal prosthesis, the optimal coil inductances have to deal with the constraints of the coil sizes, the trade-offs between loss, H-field limitation and the DC supply voltage requirement of the class-E driver. Our design starts with the formation of equivalent circuits, followed by the analysis of the loss of rectifier and coils and the H-field for induced voltage and current. Both linear and non-linear models for the analysis are presented. Litz wire is used to reduce the winding losses in our analysis. Based on the procedure, an experimental power link is implemented with an overall efficiency of 67% at the optimal distance of 7 mm between the coils.