Effective magnetic resonant wireless power transfer system over medium range using an intermediate resonant coil of two loops

This paper presents a two-loop intermediate resonant coil for the enhancement of power transfer efficiency and the reduction of magnetic fields in wireless power transfer (WPT) over medium range. Two rectangular spiral loops are connected including a resonant capacitor for the two-loop intermediate resonant coil. One of the two loops is coupled to a transmitting (Tx) resonant coil, while the other is coupled to an receiving (Rx) resonant coil. Magnetic fields can be generated at the two loops mainly and suppressed in an unnecessary region simultaneously, although the resonant coil has a large area for inductive coupling. For verification, a WPT system using the proposed intermediate resonant coil is demonstrated for a 170-watt wireless powered LED TV. The distance from the center of the Tx resonant coil to that of the Rx resonant coil is 130 cm. The power transfer efficiency of the WPT system shows 72.85%. Magnetic fields at the center of the proposed resonant coil over a 40-cm distance meet the ICNIRP public regulation.