Wireless power transfer via air and building materials using multiple repeaters

In this paper, we investigate wireless power transfer using multiple repeater antennas through air and building materials. The system architecture includes one transmitter antenna, one receiver antenna and repeater antennas in a cascade arrangement. All antennas were loop coils made of Litz wires with 15 cm-radii and 10 turns. The transmitter antenna was driven by a high efficiency class-E power amplifier (PA) while receiver antenna was connected to a load. System efficiency including both amplifier efficiency and wireless link efficiency was determined as the ratio between the output power received at the load and the input power fed into the amplifier. Theoretical model based on circuit theory was introduced to calculate the system characteristics such as power transfer, wireless efficiency and power loss induced in each antenna. Experiment setups up to two repeaters were built and conducted to validate the theory model. Experimental and theoretical results agreed well and the results confirmed the parasitic effects of building materials to the wireless power transfer system performance.