A novel method for determining the mutual inductance for 13.56MHz RFID systems

A main parameter of a 13.56 MHz RFID system is the magnetic coupling factor k respectively the mutual inductance M. In this paper a new method for determining the mutual inductance is presented. This method is based on a two-port consideration to obtain the elements of the impedance matrix of the coupling system. The mutual inductance is calculated from the impedance matrix and the coilpsilas equivalent circuit values using a physical inductor model. Furthermore the system model presented in this paper includes the capacitive coupling between the two coils. Present methods and their disadvantages are described and the new method and its improvements are explained in detail. Finally, measurement results of a present method and of the new method are compared to EM simulation results.