The coupling system in Fig. 2 consists of two identical
helical open circuit coils. The resonance is achieved by its
self-inductance and parasitic capacitance. Therefore, no external
lumped capacitor is needed. The coupling system is
represented by its equivalent circuit model shown in Fig. 3, in
which L is the self-inductance, C is the parasitic capacitance,
R is the parasitic resistance and Lm is the mutual inductance.
All the circuit model parameters are given in Table I.