Compact multi-coil inductive power transfer system with a passive peak detector circuit for wireless sensor nodes

Abstract

Abstract In Inductive Power Transfer (IPT) the misalignment between sending and receiving coils is critical and significantly influences both transfer efficiency and charging time. It can be compensated by the use of multiple coils on the sender side. However, by increasing the number of sending coils, the supply circuit becomes big, complex and not easy to control. In this paper, we propose a compact and efficient supply circuit for multi-coil IPT systems, which activates only the coil under the receiving coil. The receiver detection is based on a compact passive peak voltage detector measuring the sending coil voltage variation. The receiver coil position determination is supported by measurements of the sending coil neighbours voltages, so that a stable power transfer to battery-free wireless sensor nodes can be realized. The investigation of the influence of the type, the shape, and the size of conductive materials between sender and receiver shows that the system can distinguish between the receiver coil and different metallic objects such as iron, coins, and copper.