ISM Band
As stated in the section above, the resonance frequency
changes as the coupling factor changes, and the maximum
efficiency power transfer occurs at the resonance frequency.
Therefore, a system that matches the frequency of the power
source and the resonance frequency is needed. There are two
ways to achieve resonance. One is to match the frequency of
the power source to the resonance frequency, and the other is
to match the resonance frequency to the power source. The
former can be easily achieved by applying a feedback control
for the efficiency to the power source. However, when this
power transfer system is applied in the MHz range, the usable
frequency range is bounded by the Industrial, Scientific,and
Medical(ISM) band. According to the ISM band, the usable
frequency ranges are extremely small. For example at
13.56MHz, the range is 13.56MHz±7kHz.
As a result, to apply this technology in the MHz range, the
frequency of the power source must be fixed at a usable range,
and a tuner must be used to match the resonance frequency of
the antennas to the frequency of the power source. In this