Axial Magnetic Quadrupole Mode of Dielectric Resonator for Omnidirectional Wireless Power Transfer

Omnidirectional wireless power transfer systems have been studied intensively due to an increasing demand for charging arbitrary spatial devices. To achieve omnidirectional wireless power transfer with high efficiency, a high Q-factor transmitter coil that can generate homogeneous magnetic field is crucial. In this paper, we develop an omnidirectional magnetic resonant wireless power transfer system based on a disk resonator with colossal permittivity and low loss. We propose to operate at axial magnetic quadrupole mode of the transmitter resonator to produce a homogeneous magnetic field in the transverse plane. The constant power transfer efficiency of 88% at the frequency of 157 MHz over the transfer distance of 3 cm for all angular positions of a receiver is experimentally demonstrated. The possibility of multi-receivers charging is also studied and a total efficiency of 90% regardless of angular position between two receivers is demonstrated experimentally

Miniature Wireless Power Transfer System for Charging Vertically Oriented Receivers

Development of compact wireless power transfer (WPT) systems for charging miniature randomly oriented electronic devices is quite a challenge. Traditionally, WPT systems based on resonant magnetic coupling utilize face-to-face aligned transmitter and receiver coils providing sufficient efficiency at relatively large distances. However, with the presence of angular receiver misalignment in a such system, the mutual coupling decreases resulting in a low power transfer efficiency. Here we develop a compact WPT system for wireless charging of miniature receivers vertically oriented with respect to the transmitter. As a transmitter, we employ a butterfly coil that provides a strong tangential component of the magnetic field. Thus, a vertically oriented receiver located in the magnetic field can be charged wirelessly. We perform numerical and experimental studies of the WPT system power transfer efficiency as a function of the distance between the transmitter and the receiver. The misalignment and rotation dependencies of power transfer efficiency are also experimentally studied. We demonstrate the power transfer efficiency of 60 % within transfer distance of 4 mm for a vertically oriented receiver with an overall dimension of 20 mm X 14 mm at the frequency of 6.78 MHz