Transferred power and efficiency of a coupled-resonator WPT system

A coupled-resonator WPT system is analyzed in terms of transferred power and transfer efficiency. Quality factor (f_m) of the coupled resonators is defined by the product of the coupling coefficient (k) and unloaded Q (Q₁, Q₂) of the resonators. Though it is well known that the maximum value of transfer efficiency is determined only by f_m, its condition has been unrealistic. The present paper gives a new expression that is not only far more realistic but also physically acceptable. In addition, the operating frequency selection method for the case of double peak response due to the over-coupling is proposed. A widely accepted method of the peak preference is criticized.