Resonance in anisotropic layered media

Abstract – When a periodic anisotropic layered medium is interrupted by a slab of contrasting material, electromagnetic resonance can be manifest in a variety of ways. In one scenario, anisotropy allows for fre-quency intervals in which waves propagating perpendicular to the layers coexist with evanescent waves. This permits energy to be trapped within the slab at frequencies embedded in the continuous spectrum. These are unstable states that result in resonance under small perturbations. In another scenario, a stationary inflection point in the dispersion relation of an ambient magnetic anisotropic layered medium leads to unidirectional propagation and resonant interaction between Bloch waves and the contrasting layer. Analysis of energetic interactions between waves allows for a detailed understanding of these resonances. I. RESONANCE IN SLAB STRUCTURES When a periodically layered medium is broken by a finite-width slab of a contrasting layered medium (Fig. 1), resonant interaction between an electromagnetic source field and the slab can result in anomalous scattering behav-ior. This study concerns resonance of a particular nature. We consider the situation in which the structure supports a harmonic electromagnetic field at a specific frequency in the absence of any source field originating from outside the slab (a source-free field). Such a field is dynamically decoupled from energy-transporting harmonic waves in the ambient medium. But when the parameters of the system are perturbed (structure, frequency, angle of incidence)