Incident-Angle-Dependent Extraordinary Transmission of the Terahertz Bull’s-Eye Structure

The bull's-eye structure in the terahertz (THz) frequency region has ample applications owing to its ability focus free-propagating waves into subwavelength apertures, resulting enhanced transmission, that is, extraordinary transmission. However, coupling properties have been primarily discussed terms of normal plane-wave incidence structure. In this study, we investigate multiple resonances transmission with and oblique incident waves. experiment using a widely tunable high-power THz wave source revealed two types resonances. main resonance split depends on angle, other corresponds side lobe results are explained by simple analytical model finite number scattering media. analysis is supported full-wave simulation finite-element method, which agrees experimental results. mechanisms will be applicable design devices, such as biosensing devices or antennas for rapid communication systems.