Zero Backscattering From Self-Dual Objects of Finite Size

Duality transformation is applied to the theory of zero backscattering from finite objects. It is shown that if the object, defined by medium and/or boundary condition, is self dual, i.e., invariant in the duality transformation, it is invisible to radar if a certain condition for the polarizability dyadic is valid. This is a general statement and includes previous theorems as special cases. As novel self-dual objects those with boundary conditions requiring vanishing of the normal components of the D and B vectors ("DB boundary") or their normal derivatives ("D^\´B^\´ boundary") are introduced. As examples of zero-backscattering objects, scattering properties of a sphere and a cube with DB or D^\´B^\´ boundary, as well as an anisotropic asymmetric spheroid, are discussed.