Holding magnets and magnet system for implantable systems optimized for MRI

An implant device comprising:

• signal processing circuitry configured for receiving an implant communications signal transmitted from an external transmitting coil through overlying skin of a patient, wherein the implant device includes an outermost surface adapted to lie between the overlying skin and underlying skull bone of the patient;
• a magnet case configured to be rotatable about a case rotation axis which is at least approximately perpendicular to the outermost surface of the implant device;
• and
• an implant magnet arrangement within the magnet case configured to cooperate with an external holding magnet in an external device to be located over the overlying skin to magnetically hold the external device against the overlying skin;
• wherein the implant magnet arrangement comprises a plurality of cylindrical magnets, each with a center cylinder axis perpendicular to the case rotation axis, and each cylindrical magnet configured to be rotatable about the center cylinder axis;
• wherein each cylindrical magnet has an outer cylindrical surface with a north magnetic pole and a south magnetic pole;
• wherein a north magnetic direction is defined by a radial vector extending from the center cylinder axis to the north magnetic pole;
• wherein a south magnetic direction is defined by a radial vector extending from the south magnetic pole to the center cylinder axis;
• and
• wherein, for at least two of the plurality of cylindrical magnets, the north magnetic pole and the south magnetic pole for a given cylindrical magnet are arranged with respect to each other so as not to lie on a common diameter through the center cylinder axis such that the north magnetic direction and the south magnetic direction form a magnetic angle less than 180 degrees with a vertex at the center cylinder axis.