Resonances of periodic metal-dielectric structures at the infrared wavelength region

Metal meshes have been used as reflectors in radar receivers for wavelength much longer than the periodic constant of the conducting wires and as optical reflectors in a Fabry-Perot in the far infrared. Cross shaped metal meshes can be used as band pass filters but the design theory and near field properties have not been known. Transmittance of thin, single-layer and multiplayer metal meshes has been investigated using Micro-Strips, yielding numerical solutions of Maxwell's equations. The near field effect was studied for two alignment configurations of cross shaped metal meshes, both free standing and with dielectrics, and transmission line theory was applied for the interpretation as an oscillator mode model. The model for the interpretation of the mode of a single mesh uses a pair of coupled surface wave (that is one standing wave on each side). The transmittance of multi-layer metal meshes are interpreted as modes composed of resonance modes of the single mesh, the Fabry-Perot modes depending on the separation of the meshes, and their interaction. Experimental data for thick inductive cross shaped metal meshes agree very well with Micro-Strips calculations in the long wavelength region and with Fourier Modal method calculations in the short wavelength. The transmittances of all these meshes show similar resonance peaks and the same dependence on thickness of the short wavelength peaks, suggesting that the interpretation using the oscillator mode model is valid in the short and long wavelength region. Stacks of thin metal meshes have been studied with Micro-Strips and transmission line theory. Narrow transmission regions for inductive meshes and narrow bandgap regions for capacitive meshes may be obtained from layered structures for the aligned configuration and spacing of 1/4 resonance wavelength of a single layer.