Inductive Power Transfer (IPT) is well-established for applications
with biomedical implants and radio-frequency identification
systems. Recently, also systems for the charging of the batteries of
consumer electronic devices and of electric and hybrid electric vehicles
have been developed. The efficiency of the power transfer of IPT
systems is given by the inductor quality factor Q and the magnetic
coupling k of the transmission coils. In this paper, the influence of the
transmission frequency on the inductor quality factor and the efficiency
is analyzed taking also the admissible field emissions as limited by
standards into account. Aspects of an optimization of the magnetic design
with respect to a high magnetic coupling and a high quality factor are
discussed for IPT at any power level. It is shown that the magnetic
coupling mainly depends on the area enclosed by the coils and that their
exact shape has only a minor influence. The results are verified with an
experimental prototype.