Geometry-based optimization of radio-frequency coils for powering neuroprosthetic implants

Biomedical implants powered by inductive links have several advantages over batteries or percutaneous power linkages. The inductive link power transfer efficiency must be optimized to realize the full advantage over other power delivery technologies. Optimization is also important to reduce the electromagnetic radiation exposure, reduce secondary heating effects and improve power efficiency, so that large primary side storage batteries are not required. Geometric constraints, i.e., size and shape, of biomedical implants are a primary concern of device design. In this paper, we present a novel coil optimization strategy driven by geometric constraints. By considering the relationship between wire diameter, number of turns, quality factor, coupling coefficient and shape of coil, we can optimize the inductively coupled coils to maximize the power transfer efficiency under stringent geometric constraints. This new approach is verified using a design example targeted for an intraocular visual prosthesis. In this example, we demonstrate an experimental power transfer efficiency of 52 % by co-optimization of the primary and secondary coils.