Reduction of AC resistance in MEMS intraocular foil coils using microfabricated planar Litz structure

The next-generation implantable high-power prosthetic devices, such as retinal prostheses, will be powered by inductively coupled coils of high efficiency. However, the use of high-frequency power carriers almost always induces significant AC resistance due to skin and proximity effects, which limits the overall coupling efficiency. Inspired by the widely used round Litz wire, planar coils with planar Litz structures were investigated on the printed circuit board (PCB) and showed the reduced AC resistances in some specific frequency ranges. Herein, various planar Litz structures were introduced into previous MEMS foil coils, which have been proved to be superior over the conventional planar counterparts. The experimental results provided by the aforementioned prototypes showed a reduction of AC resistance up to 13.3% compared to a solid foil coil. A microfabrication process, which combines a single layer metal deposition and patterning with a post folding step, was developed to construct the planar Litz structure.