Wireless power transfer system based on toroidal metamaterials
Authors: Zhao Jun-Fei  , Zhang Ye-Wen  , Li Yun-Hui  , Chen Yong-Qiang  , Fang Kai  , He Li  ,   School of Physics Science and Engineering, TongJi University, Shanghai 200092, China;,   College of Electronics and Information Engineering, TongJi University, Shanghai 200092, China
Published: December 2020

Now, the traditional four-coil magnetic coupling systems have been used in the wireless charging of mobile electronic devices and electric vehicles. However, the system efficiency is difficult to improve due to the divergence of spatial distribution of magnetic field. To overcome this disadvantage, we propose an efficient system based on the toroidal metamaterials, which support a resonant electromagnetic mode that is dominated by the toroidal moment. The toroidal moment is produced by currents flowing on the surface of a torus along its meridian. It presents remarkable ability to localize the field and suppress the radiation.
This new toroidal magnetic mode system (TMMS) consists of four asymmetric split resonant rings (ASRRs). Pairs of ASRRs in the same unit (transmit unit and receiver unit) have mirror symmetry about the yz plane. Pairs of ASRRs in different units have 180 rotational symmetry about the x axis. These four rings support the toroidal magnetic resonant mode (dominated by toroidal moment). For comparison, we also construct two symmetric split resonant rings to imitate the four-coil system (FCS). It supports parallel magnetic mode (dominated by magnetic dipole moment) and antiparallel magnetic mode (dominated by magnetic dipole moment and magnetic quadrupole moment).
To confirm the improvement of efficiency, we compare the transmission of the TMMS with that of the FCS at the same transfer distance (10 mm). The TMMS presents a higher transmission and the increase in simulation (experiment) is 81% (40%). The toroidal magnetic mode in the TMMS also exhibits low metal loss, which is reflected in these spectra. The simulated distributions of magnetic field line corresponding to the resonantly magnetic modes in both systems are provided in this article. Instead of divergence in FCS, the magnetic field lines of TMMS are well constrained around the four rings and form closed loops along these rings. The density of the field line and the magnitude of field near the receiving coil are both enhanced. So the system efficiency, which is determined by the magnetic flux of the receiving coil, is improved. The dispersions of radiation power for various induced multipole moments from the two systems are also calculated. The dominance of toroidal moment corresponding to the resonant mode in TMMS is verified and the radiation is suppressed to 1/4 of FCS. Finally, the transmissions of two systems at different transfer distances are presented. The toroidal magnetic mode system presents a higher efficiency at strong coupling area (0-25 mm). The average increase of the transmission in simulation (experiment) is 73% (46%).
In summary, the proposed new system exhibits the properties of high efficiency, low metal loss and low radiation loss with the multiport output. It would have broad prospects of practical application in WPT.