Estimates for the low-frequency electromagnetic fields scattered by two adjacent metal spheres in a lossless medium

International audienceInductive electromagnetic means, currently employed in real physical applications and dealing with voluminous bodies embedded in lossless media, often call for analytically demanding tools of field calculation at modeling stage and later on at numerical stage. Here, one is considering two closely adjacent perfect conductors, possibly almost touching one another, for which the 3D bispherical geometry provides a good approximation. The particular scattering problem is modeled with respect to the two solid impenetrable metallic spheres, which are excited by a time-harmonic magnetic dipole, arbitrarily orientated in the 3D space. The incident, the scattered, and the total non-axisymmetric electromagnetic fields yield rigorous low-frequency expansions in terms of positive integral powers of the real-valued wave number in the exterior medium. We keep the most significant terms of the low-frequency regime, that is, the static Rayleigh approximation and the first three dynamic terms, while the additional terms are small contributors and they are neglected. The typical Maxwell-type problem is transformed into intertwined either Laplace's or Poisson's potential-type boundary value problem with impenetrable boundary conditions. In particular, the fields are represented via 3D infinite series expansions in terms of bispherical eigenfunctions, obtaining analytical closed-form solutions in a compact fashion. This procedure leads to infinite linear systems, which can be solved approximately within any order of accuracy through a cutoff technique