RESONANT EXCITATION OF A 2D PERIODIC SCREEN PERFORATED BY CIRCULAR BELOW-CUTOFF HOLES

摘要

Features of plane wave scattering by two-dimensional periodic perforated screen with a few sub-wavelength holes over the period are analyzed. It is shown that in contrast to single-element screens (with one hole over the period) such screens show dual properties. Specifically, operating in the single-wave regime they can support both the total transmission and/or total reflection resonances. The resonance behavior like this is explained within the spectral theory. It is shown that the spectrum structure of the complex-valued frequencies of the multi-element screen being considered as an open resonator is already built into the spectrum of a simple single-element screen if a model with macroperiod accommodating several identical cells is considered. Lower-order eigen oscillations of multi-element screens which appear due to various kinds of defects in the cell geometry are analyzed. A simple approximation model describing the dependence of the resonance response as a function of the eigenfrequency spectrum of lower-order modes is used to analyze possible types of the scattering characteristics within the single-wave range.