Novel material with narrow-band transparency window in the bulk

This paper presents the theoretical design of an artificial dielectric exhi biting narrowband frequency selective properties in the bulk without relyin g on periodic placement of elements. In this manner, it initiates a novel a pproach that bypasses the draw;backs of the traditional frequency selective surfaces (FSS), namely, unwanted passbands, dependence on excitation angle and polarization, and difficulties in conversion from planar to curved geo metries, The key design elements are the concentric geometry of the inclusi ons and the use of Lorentzian resonant media. A discussion of physical reso nant materials is presented, substantiating the credibility of the theoreti cal design. To illustrate the approach, a novel complex medium is synthesiz ed as an ensemble of spherical particles composed of a lossy core coated wi th a highly resonant dielectric layer and embedded into a dielectric host. The resulting structure is an amorphous substance, lossy over its entire sp ectrum except for two narrow-band transparency windows, where it may become as lossless as desired. The parameter space of the system is thoroughly an alyzed which determines the type of constitutive materials and geometries f or tailor-designing the windows according to specifications (shape, positio ning and overall normalization). In this sense, the lossy concentric struct ure forms an ideal candidate for thin absorbing films (TAF's) with extensiv e applications in antenna systems, RF absorbers, and anechoic chambers.