Achieving Uniform Magnetic Field with Rectangular Coil in Wireless Power Transmission System

A resonant inductive wireless power transmission (WPT) system consists of loosely magnetically coupled transmitting and receiving coil. At some distance from a rectangular transmitting coil, magnetic field that is generated by a flow of current through such a coil is expected to be approximately uniform in a rectangular plane above and parallel to transmitting coil. Criterion chosen to determine approximately uniformity of magnetic field intensity in a plane is that magnitude of magnetic field intensity is within +/- 10% with respect to the magnitude of magnetic field intensity in a center of such plane. Evaluation of planar uniformity of magnetic field intensity for various distances from transmitting coil was carried out by simulations in Ansys Maxwell 18 software. According to simulation results, aforementioned criterion is satisfied when the plane is 189 mm above the rectangular transmitting coil (165 cm by 45 cm). Planar non-uniformity, i.e. any significant change in magnitude of magnetic field intensity will in turn significantly change the voltage induced at the receiving resulting in either too low or too high voltages. With low voltage the receiving circuit will not work properly, and high voltage levels can cause receiving circuit damage. Hence, uniformity of magnetic field intensity ensures safe and uninterrupted operation of WPT system.