Intermediate Range Wireless Power Transfer With Segmented Coil Transmitters for Implantable Heart Pumps

In wireless power transfer systems, substantial differences in transmission range and alignment sensitivity can occur when the transmitting coil dimensions are varied. A coil with larger inner and outer diameter was found to provide a wider transmission range and lower alignment sensitivity. Accordingly, we developed a larger coil (24x30 cm(2)) designed to be embedded in the back of a vest to power dc pumps for artificial hearts or left ventricular assist devices. To significantly reduce the required transmitting coil voltage, the coil was divided into eight segments with resonant capacitors. The coil was operated at 6.78 MHz and evaluated with a 5.3-cm diameter receiving coil. A circuit model for the energy coupling coils was developed to predict the output power and efficiency. Having a coil separation of 7.7 cm, we measured an output power of 48.2 W and a corresponding energy efficiency higher than 80%. The energy coupling coils were also evaluated with a dc pump in parallel to an additional load representing the power consumed by auxiliary circuits of an implanted heart pump. Experimental results showed that the proposed coil segmentation technique for mid-range wireless energy transfer can significantly reduce the transmitter voltage to a safe level (similar to 10 V-rms).