Omnidirectional Wireless Power Transfer System Using Modified Saddle-Shaped Coil Pair for Implantable Capsule Robots

Wireless power transfer (WPT) technology has been widely researched and developed, especially the omnidirectional WPT system. Despite much attention, the omnidirectional WPT system generating 3-D magnetic field is rarely reported for capsule robot (CR) applications. In this article, we propose a genuine omnidirectional system for CR using only one pair of power transmitting coils (PTCs) and one power receiving coil (PRC) for the first time. The novel PTC with a compact and compatible structure is capable of generating 3-D magnetic field at any position. In particular, a single power source is solely utilized to drive the PTC without current amplitude or phase control methods. Based on the magnetic calculation and finite-element simulation, the geometric parameters of the proposed PTC structure are determined. Additionally, through the theoretical analysis and comparison with traditional topology, the capability of omnidirectional transfer can be verified. Furthermore, in order to dynamically adjust the PTC rotation, the corresponding received voltage tracking-based control strategy is also illustrated. Finally, a practical prototype is built, and experimental results confirm the omnidirectional WPT capability of the proposed system concerning both positions and attitudes, as well as the effectiveness of the control method. It demonstrates a maximum power delivered to the load of 2523 mW with a power transfer efficiency of 8.4%.