SELF-TUNING INDUCTIVE POWERING FOR IMPLANTABLE TELEMETRIC MONITORING SYSTEMS

Inductive powering of implantable monitoring devices is a widely accep ted solution for replacing implanted batteries. However, this method d emands technically skilled operators to tune constantly the power link parameters. This becomes particularly important when the external sys tem must also be portable. However, acceptable lifetimes for the exter nal batteries can be obtained by a precise optimization of the power e fficiency of the inductive link. In this paper, a technique is present ed to render such a portable system fully compatible with a hospital e nvironment. It is implemented in an independent, automatic and user-fr iendly powering set-up to avoid the need for engineers or additional e lectronic equipment for optimization of the link parameters. Multiple automatic tuning loops are incorporated to handle component tolerances and coil movements, and to optimize the power efficiency on a continu ous basis. A visual and an acoustic indicator give the operator an add itional feedback on the quality of the established link. As an example , the problem of mechanical strain sensing in femoral nailplates is gi ven. It is representative for the envisaged range of applications. The se are characterized by a low coil coupling (k less than 1%) and power transfers of the order of 20 mW.