This paper presents an analysis for electromagnetic energy in dispersive composite media based on classical electrodynamics. An investigation of the relation between reactance rate and electromagnetic energy derived from the Fosters theorem is conducted. The material energy of this kind is discussed in the frequency band of the left handed property. It is illustrated that the time average electromagnetic energy density is still positive even after an effect of dissipation is cancelled in the left handed band, which is reasonable in physics.

In this article, a new structure of dual band pass FSS is simulated and analyzed. The improved FSS structure, which satisfies the requirement of miniature, is much simpler than traditional one and has lower working frequency band, and it provides a new way to solving the problem of the coupling effect of dual bands. Besides, its response towards electric field is invariant. The response has no obvious change when the incident angles change a lot.