Wireless power feeding was examined with strongly coupled magnetic resonance for an object moving in 3-D space. Electric power was transmitted from the ground to an electrically powered toy helicopter in the air. A lightweight receiver resonator was developed using copper foil. High Q of greater than 200 was obtained. One-side impedance matching the transmitter side was proposed to cope with high transmission efficiency and the receiver’s weight reduction. Results show that the efficiency drop near the ground was drastically improved. Moreover, the measured efficiency showed good agreement with theoretical predictions. A fully equipped helicopter of 6.56 g weight was lifted up with source power of about 5 W to an altitude of approximately 10 cm

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Wireless power transmission using magnetic resonance is discussed. Theoretical transmission efficiency was derived as a function of impedance ratio r and RF frequency ω. Impedance matching is possible to attain maximum transmission efficiency for various coupling coefficient cases. Power feeding demonstration to an electric powered helicopter was conducted to develop an efficient, compact, and light-weight resonator as a receiver and to show the validity of the theoretical prediction. In this system, dielectric loss of the capacitor was found predominant and is liming the quality factor Q of the resonator.

Wireless power feeding transmission is now in demand in the various fields. Electrical products of this modern age such as mobile phones, laptop monitoring sensors and electrical vehicles are spreading everywhere. Those electric device need to feed frequently because amount of consumed electric power of those devices are gradually increasing. Nonetheless content of battery show signs of leveling off. This is why it is important to develop a method of wireless power transmitting system with high efficiency. Strongly coupled magnetic resonance is the latest type of wireless power transmission technology. The main feature of this technology is the effectiveness in the mid-range that covers many attractive applications. The theory of transmitting efficiency is derived as a function of impedance ratio r and RF frequency ω. NOMENCLATURE C = capacitance fom = figure-of-merit, fom=kQ=ω 0 M/(R S R D ) 1/2 I = complex electric current k = coupling coefficient, k = M/(L S L D ) 1/2 L = self inductance M = mutual inductance Q = quality factor of resonator, Q= ω 0 L/R R = resistance of electric circuit r = impedance ratio, r= Z 0 /R V = complex electric voltage Z = complex characteristic impedance, Z=R+j(ωL -1/ωC) η = transmission efficiency θ = phase difference ω = angular velocity SUBSCRIPTS S = source, transmitter side D = device, receiver side src = power source ld = load