Nested Equivalent Source Approximation for EM scattering by penetrable bodies

The Boundary Element Method (BEM) discretization (also known as Method of Moments - MoM - in computational electromagnetics) is particularly well suited for solving time harmonic electromagnetic problems, for a large class of practical problems: typical examples are metallic scatterers, or scatterers composed by only a few different homogeneous materials (as opposed to, e.g., the human body). However, the efficient solution of large BEM problems is still very challenging, due to the dense matrix it yields. Fast solvers, i.e. proper factorizations of the system matrix reducing storage and CPU requirements, are usually necessary to handle large meshes.