Exactness of the first born approximation in electromagnetic scattering

For the scattering of plane electromagnetic waves by a general possibly anisotropic stationary linear medium in three dimensions, we give a condition on the permittivity and permeability tensors of the medium under which the first Born approximation yields the exact expression for the scattered wave whenever the incident wavenumber k does not exceed a pre-assigned value α. We also show that under this condition the medium is omnidirectionally invisible for k ≤ α/2, i.e., it displays broadband invisibility regardless of the polarization of the incident wave.