Monochromatic Tuning of Absorption Strength Based on Angle-Dependent Closed-Ring Resonator-Type Metamaterial Absorber

In this study, almost monochromatic tuning of absorption strength, i.e., tuning the absorption peak level at almost the same frequency, is presented by using an angle-dependent closed-ring resonator (AD-CRR)-type narrowband absorber structure in S-band. With this aim, first an ordinary planar closed-ring resonator (CRR) structure having a ground plane is designed, and then the structure is folded inward by a rotation angle α from α = 0° (i.e., a planar CRR) to α = 60° along the center line, which is parallel to the incident electric field. Both simulation and experimental results agree with the fact that the rotation angle α provides the freedom of tuning the absorption strength of the absorber structure almost monochromatically.