Wireless Power Transfer for Smart Knee Implants

An inductive link based wireless power transfer methodology is described for a smart knee implant designed to continuously monitor the loads on the knee. The primary and secondary coil dimensions and wireless link characteristics are first optimized via an equivalent lumped electrical model. The wireless link is then simulated with more accurate 3D field simulations. The impact of the package and various layers of tissue between the coils on the quality of the link is investigated. The effects of potential misalignments between the coils are also analyzed. When the distance between the coils is 39 mm and the input power to the primary (external) coil is 2.5 W, approximately 0.35 mW of power can be received by the secondary coil that is located within the implant.