Reactive component selection for TET powered medical devices

Transcutaneous energy transfer (TET) is capable of supplying power across the skin to implantable devices and avoids the risk of infection associated with wires passing through the skin. These systems rely on a high frequency magnetic field to overcome the relatively low coupling between a coil located outside the body, and a coil implanted within the body. This paper introduces a new optimisation procedure to choose tuning capacitors that minimises the amount of power dissipated in the power transfer coils of an implantable TET system. The frequency of operation is determined by the selection of the resonant reactive components. By analysing 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. The method is used to find the value of the resonant capacitors for a system delivering 15W over a coupling range of k=0.1 to 0.55 (corresponding to a separation of up to 20mm).