Sphere-Shaped Receiver Coil for Misalignment-Resilient Wireless Power Transfer Systems for Implantable Devices

Positional misalignments of coils cause a sharp drop in the power transfer efficiency (PTE) of wireless power transfer (WPT) systems. To minimize this deterioration of the PTE, this study introduces a sphere-shaped (Rxs) to a three-coil magnetic resonance-coupled WPT system for implantable devices. To assess the significance of Rxs, its performance was compared to the well-known circular planar (Rxf), half-sphere-shaped (Rxhs), and solenoid (Rsl) coils. Moreover, a small and efficient voltage doubler as a rectifier was designed. This voltage doubler has a high conversion efficiency of 89% with an output voltage of >3 V at 15 dBm. To validate the concept, prototypes of the coils and voltage doubler were fabricated and measured in saline and minced pork. The PTEs of the Rxf, Rxhs, Rsl, and Rxs coils-based WPT systems were studied under different lateral and angular misalignments in both simulations and measurements. In perfect alignment conditions, the measured PTEs of Rxf, Rxhs, Rsl, and Rxs WPT systems were 7.68%, 10.18%, 25.01%, and 22.38%, respectively; however, when the (Rx) receiver coils rotated by 90°, the PTEs were 0%, < 0.2%, 0.15%, and 5.4%, respectively. Under lateral misalignments of
$dx =25$
mm, the PTEs were 0.82%, 1.91%, 2.4%, and 4.87%, respectively. Furthermore, the PTE for the Rxs-based WPT system was measured in saline- and minced-pork-filled boxes and a saline-filled American Society for Testing and Materials (ASTM) model under different misalignment conditions to expand its applicability range to deep-body non-static implants. Both the simulated and remeasured results show that the proposed Rxs-based WPT system presented an improved and stabilized PTE under positional misalignments.