Condition for the general ideal boundary

The electromagnetic ideal boundary is defined as a surface on which the complex Poynting vector has no normal component. Examples of such boundaries are the perfect electric and magnetic boundaries, as well as the soft-and-hard surface with its recent generalization. In the present study, the general ideal-boundary condition is introduced, and basic properties of plane-wave reflection from a planar boundary are studied in terms of normally and obliquely incident plane waves. It is seen that, in the general case, an incident wave is reflected in two directions. A special self-dual ideal planar boundary has the interesting property of being a perfect back-reflector for a plane wave incident from any direction.