Influence of distance and frequency variations on wireless power transfer

Distance and frequency variation are the main causes for dramatic decrease of the output power and efficiency in wireless power transfer system. The influence of these parameters should be considered from the design stage. This paper investigates the effect of distance and proposes a method to estimate the distance with maximum output power for air-core coils. The effect of operating frequency focused on the frequency splitting phenomena is investigated. Results have shown that tighter coupling does not always result in higher power transfer. An optimal distance corresponding to the maximum power transfer is proposed. Regardless of the frequency splitting phenomena, the critical coupling distance is determined using the proposed method for the maximum power transfer.