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 $\text{1}\%$ fractional bandwidth for more than $\text{90}\%$ 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 $\text{50}\%$ 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.