A study of coil orientations to enhance the transfer efficiency of a multi-repeater wireless power transmission system

In this work, we investigated the feasibility of improving wireless power transfer (WPT) efficiency for long ranges using multiple repeaters with antenna orientation enhancement. The system architecture included one transmitter antenna (TX), one receiver antenna (RX) and repeater antennas (RP) in a cascaded arrangement. In our experiments, 15 repeaters were used for demonstration. The spacing between adjacent antennas was 30 cm and the overall distance from TX to RX was 4.8 m. Identical antennas were made of 46 AWG, 145-strand Litz wires in 10 turns of coils which have a size of 60 cm × 60 cm in a rhombic shape. In the transmitter circuit, a class-E power amplifier was used to convert power from DC supply to 900 kHz while a 100-Ω resistive load was used in the receiver circuit to harvest the wireless energy. The system efficiency was measured as the ratio between the output power delivered to load and the input power from the DC source. Theoretical model based on inductive coupling was presented to calculate the system characteristics such as power transfer between antennas, power loss induced in each antenna and total wireless power transfer efficiency. Calculation and measurement results matched well and both confirmed the effects by coil orientation variations in a WPT system.