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Improved Wireless Power Transfer Efficiency Using Reactively Terminated Resonators

To increase the efficiency of a wireless power transfer system, a method based on optimizing the product of coupling coefficient by quality factor (kQ) of the resonators has been proposed. In this method, efficiency is improved by tuning the resonance frequency at a value where kQ has a maximum. This is carried out by a terminating capacitor for the resonators. In this case, the resonance frequency is less than the self-resonance frequency. However, the capacitance of the tuning capacitor is small enough to ensure that both electric and magnetic coupling will contribute to power transmission. Applying the proposed method to two square 18 cm × 18 cm antidirectional spiral resonators at a spacing of 270 mm, the efficiency is increased to 20% compared with 13% at the SRF. Moreover, the proposed method desensitizes the power transfer efficiency to the nearby objects.