A Solution to Frequency Splitting in Magnetic Resonance Wireless Power Transfer Systems Using Double Sided Symmetric Capacitors

The technology of wireless power transfer using magnetic resonance coupling has become a subject of interest for researchers with the proliferation of mobile. The maximum efficiency is achieved at a specific gap between the resonators in the system. However, the resonance frequency splits as the gap declines or gets smaller. Different methods have been studied to improve this such as frequency tracking and impedance matching, including capacitive tuning. However, the system has to maintain the same working frequency to avoid moving out of the license exempt industrial, scientific, and medical (ISM) band; and the efficiency must be as large as possible. In this paper, a symmetric capacitance tuning method is presented to achieve these two conditions and solve the splitting problem. In the proposed method, the maximum efficiency at one of the splitting frequencies is moved to match the original resonance frequency. By comparison to other works, both simulation and experiment show considerable improvements for the proposed method over existing frequency tracking and impedance matching methods. The paper also presents a proposal to apply this method automatically which can achieve wireless charging for electronic applications with high efficiency and through variable distance.