Spatially Arranged Relay Coils to Improve the Misalignment Tolerance at an Enhanced Transfer Distance

Wireless power transfer (WPT) systems use relay coils to increase output power over longer distances. This article presents a novel arrangement of distributed relay coils that improves lateral misalignment tolerance at high transfer distances. The relay coils are optimized using techniques based on a magnetic field forming method by employing an EM simulator to determine the position and geometrical parameters of the relay coils. The optimized design consists of five relay coils, four above the transmitter (Tx) coil's periphery and one above the center. The proposed design enhances the uniformity of the magnetic field in the receiver (Rx) region, enabling greater freedom in Rx coil displacement. The authors evaluated the design's performance based on the achieved uniformity factor of the magnetic field and mutual inductance, which are determined as {\text {UF}_{\text {H}}=61.22\%} and {\text {UF}_{\text {M}}=15.28\%} , respectively, at a transfer distance of 100 mm. The authors fabricated the relay coils using Litz wire on a transparent arsenic sheet at different heights to validate the proposed design. After that, the magnetic field, transmission coefficient ( {\text {S}_{21}} ), and power transfer efficiency (PTE) profiles are experimentally measured. The measured results are found to be consistent with the simulated findings, demonstrating the effectiveness of the proposed relay coil arrangements.