nce.
Fitting curves were drawn by the fourth-order polynomial
least square. For short transmission distances, the power simply
depends on the magnetic pole area, so that similar results are
obtained for P2 and P3. However, for distances above 50 mm,
a clear effect of the pole-piece shape is observed, with higher
transmitted power being achieved by P3.
A feature of the present study was the choice to use 60 Hz.
The variation in the maximum efficiency with different power
supply frequencies is discussed in this section. The permeability
(μ) and rc of themagnet pole piece strongly depend on the power
supply frequency. Fig. 7 shows the frequency dependence of μ
and rc . Here, μ was measured under the same magnetic flux
density (0.59 T) with a transmission distance of 50 mm for
P3. Frequencies over 550 Hz could not be measured due to the
limit of the power supply unit. The frequency dependences of
both parameters were consistent with previous findings [19],
[20]. We calculated the power supply frequency dependence
of the maximum efficiency and power loss using (12) and the
experimental results shown in Fig. 7. The results shown in Fig. 8
were obtained with a transmission distance of 50 mm for P3.