Use of defined ferromagnetic materials for optimized implant coil coupling

A coil arrangement is described for an implantable medical system. A coil winding has a planar ring shape winding that encloses a coil interior area. The coil winding is adapted for placement parallel to a corresponding partner coil for communication of an implant link signal having an associated magnetic field component characterized by a coupling factor k representing fractional amount of magnetic field coupling between the coils. A coil coupling lens of magnetic conductive material has multiple lens surfaces and is adapted to shape the magnetic field component to increase the coupling factor and minimize self-heating of adjacent tissues due to the magnetic field component.