In the magnetically coupled resonant wireless power transfer system, resonant coil structure is the key factor affecting the power transmission efficiency. Based on the circuit theory, the expression is deduced for the relationship between power transmission efficiency and circuit parameters. The power transmission efficiencies of the tapered resonant coil and the helical resonant coil were comparatively studied by numerical calculation. The results show that the energy transmission efficiency of the tapered resonant coil is higher when the axial spacing is within a certain range. The relationship between the structural parameters of the tapered resonant coil and the power transmission efficiency was further studied, and the optimization criterion of the resonant coil structure was proposed. The experimental results demonstrate that the power transmission efficiency of the tapered resonant coil is higher than that of the helical resonant coil.
