Study of the choice of the origin in spherical harmonics expansion for magnetic near-field sources

Using the method of multipolar expansion in spherical harmonics, the electromagnetic interference between two systems can be determined from their equivalent models. However, a multipolar expansion depends on the position of the origin: a bad choice can yield a complicated equivalent model, even for a simple source. As a consequence, the calculation of the coupling between two sources can also become more complex and require a high degree of the multipolar expansion to reach the convergence. In this paper, we propose a method to find the optimal origin for the spherical harmonics expansion. The approach can also be exploited for the localization of the electronic components in a black box.