Using S parameters in wireless power transfer analysis

This paper presents the correct formulation of scattering parameters S, using electric circuit theory, and the practical use of these parameters. The purpose is to make more efficient the processes for the information transmission and the wireless electromagnetic energy transfer. The efficiency is seen from the transmission point of view of the signals (from the transmitter to receiver) and from the active power transfer efficiency point of view (from the wireless system's input to the loads connected at their outputs). Starting from the correct formulation of S parameters, their computation takes place automatically based either on state equations or on modified nodal equations of the wireless power transfer systems (WPTS). The two magnetically coupled coils, considered as a passive linear 2-port network in harmonic regime, can be described by a number of equivalent circuit's parameters, such as: the transfer coefficients matrix T, the impedance matrix Z, the admittance matrix Y and the matrix corresponding to S parameters. This paper presents the relationships that allow the transition from one matrix to another. To generate: the coefficients corresponding to reflection, the input and output impedances, the input-output (output-input) active power transmission efficiencies, the signal transmission efficiencies, the S, H T, Z and Y matrices, and the Smith charts, we elaborated MATLAB dedicated functions by using the existing routines form the Microwave MATLAB toolbox.