Wireless Power Transfer - help required

I was going through some IEEE papers on wireless power transfer and found that most of them employ a 4 coil system. 2 of them are resonant coils which are typically multi-turn coils and there are 2 single turn coils in each transmitter and receiver. So essentially the transmitter has a single turn coil inductively coupled to the multi-turn coil and the receiver has the same configuration. The 2 multi-turn coils are resonant at a particular frequency. What is the purpose of the single turn coil? Does it provide impedance matching? If so, can someone explain how? The resonant coils are operated at 13.56 MHz

By wireless power transfer, do you mean an RF loop antenna? What are the names of the IEEE papers?

Analysis, Experimental Results, and Range Adaptation of Magnetically Coupled Resonators for Wireless Power Transfer, IEEE Industrial Electronics, 2011.
Wireless Power Transfer via Strongly Coupled Magnetic Resonances, Science, 2007 - This is the first paper on wireless power carried out in MIT.

Well, the paper tells you that the loop and coil are behaving as a step-up transformer, and that the coil is storing energy like a tank circuit.
It's not something I'm particularly interested it so I don't have much knowledge about it, but the doc has an equivalent circuit.