Enhanced transmission through metallic plates perforated by arrays of subwavelength holes and sandwiched between dielectric slabs

This paper presents analytical and numerical studies demonstrating that a perfectly conducting metallic plate perforated by a periodic array of subwavelength holes and sandwiched in between two dielectric slabs permits enhanced transmission of electromagnetic plane waves in both the optical and microwave regimes, and this for both transverse magnetically and electrically polarized fields. The enhanced transmission mechanism is attributed to coupling between the incident plane wave and resonances supported by the perforated plate that are associated with the existence of grounded dielectric slab guided waves. The enhanced transmission phenomenon occurs in one of two regimes. In the single resonance regime, the incident plane wave couples to a resonance supported by only a single slab. The transmission coefficient magnitude peaks as the excitation frequency scans through the resonance; however, the peak magnitude decays exponentially with plate thickness. In the double resonance regime, the incident plane wave couples to resonances in both slabs simultaneously. The transmission coefficient magnitude exhibits twin peaks whose magnitudes typically are larger than those resulting from single resonances and that remain large even for plates of moderate thickness. It is demonstrated that double resonances may occur for symmetric as well as for asymmetric structures, i.e., when the two slabs are identical or different. For symmetric structures double resonances occur for any angle of incidence. In contrast, for asymmetric structures, special conditions on the period and slab parameters have to be satisfied for the structure to support one or more double resonances.