Modal Impedance Expansion Method Using Loop-Star Basis Functions

The impedance expansion method (IEM) is a circuit modeling technique for electrically very small devices based on the method of moments. In the authors' previous work, a circuit model of a wireless power transfer system was developed using the modal IEM, which utilizes the IEM and eigenmode analysis, wherein the currents on the coils were expanded into thin-wire basis functions. However, surface basis functions are required to apply the modal IEM to arbitrarily shaped conductors. In this letter, the problems arising when the surface basis functions are applied to the modal IEM are pointed out, and the cause of these problems is clarified. Then, the resolvability of these problems is demonstrated using the loop-star basis functions.