Minimizing Power Loss in Air-Cored Coils for TET Heart Pump Systems

Transcutaneous energy transfer (TET) has been shown to provide an effective means of supplying power to implantable devices by avoiding the risk of infection associated with wires passing through the skin. However, it is important to manage the heat generated by the TET systems and avoid the potential of thermal tissue damage. This paper introduces a new optimization procedure to minimize the amount of power dissipated in the power transfer coils of an implantable TET heart pump system. By analyzing the overall circuit impedance it is possible to observe that a zero voltage switched TET system may dissipate different amounts of power in the power transfer coils while delivering the same amount of power. In this study an objective function was developed to determine the best configuration of resonant capacitors for any particular set of TET coils in order to minimize power loss. A set of TET coils was characterized by their self inductance, operating coupling range and their equivalent series resistance profile. When delivering 15 W over a coupling range of k=0.1 to 0.55 (corresponding to a separation of up to 25 mm), the optimal configuration improves heating performance and provides frequency stability over the extended range of coupling variation. When compared to a traditional tuning configuration tuned to a nominal resonant frequency.