High-$Q$ Terahertz Absorber With Stable Angular Response

This article presents a narrow-band terahertz absorber using miniaturized unit cells. The absorber is made of three metallic layers separated from each other using low-loss cyclic olefin copolymer as dielectric spacers. A high quality factor (Q) is obtained using a first-order resonating structure with additional capacitive loading formed by the top two metallic layers. A circuit model is developed for the analysis and design of the proposed absorber. The designed absorber shows 1% fractional bandwidth for more than 90% absorption around a center frequency of 0.5 THz under normal incidence angle. This is equivalent to a quality factor of Q = 31, calculated at 50% absorbance. The structure shows a highly stable absorbance over a wide range of oblique incidence angles. The designed absorber has been fabricated using a microfabrication process. The measured results of the fabricated prototype are in good agreement with the simulations.