Polarization Characteristic of the Magnetic Field in Wireless Power Transfer Systems

Magnetic fields are crucial for wireless power transfer systems (WPTSs) via magnetic coupling. This paper analyzes the polarization characteristic of the magnetic field in WPTS. First, a typical WPTS and its magnetic field are modeled. The magnitude and phase distributions of the magnetic field components are calculated and discussed. By adopting polarization theory, the magnetic field in WPT is analyzed via the polarization characteristic. A unique characteristic is found. Unlike far-field polarization, the characteristic possesses the following points: first, the linear, circular, and elliptical polarization states simultaneously exist in the WPT. Second, linear polarization is the intrinsic polarization state and forms a 3-D ellipsoid; circular polarization forms two rings around with the WPTS and changes with the currents. The analysis has also been proved by simulations and experiments.