Extended electromagnetic continuity condition and generalized Huygens' principle

The electromagnetic continuity condition is extended from the classical con dition on an interface between true media to a more general one relating so urces and fields in a region between two regions of arbitrary media. The co ndition allows one to extend the classical Huygens principle to involve equ ivalent sources in a spatial region volume or on multiple surfaces. As an e xample the generalized Huygens principle is applied to the formulation of a scattering problem in terms of a surface integral equation. Also, the tran sparent absorbing boundary (TAB) condition can be interpreted in terms of t he extended Huygens principle.