Terahertz carpet cloak based on a ring resonator metasurface

In this work we present the concept and design of an ultrathin (λ/22) terahertz (THz) unidirectional carpet cloak based on the local phase compensation approach enabled by gradient metasurfaces. A triangular surface bump with center height of 4.1 mm (1.1λ) and tilt angle of 20° is covered with a metasurface composed of an array of suitably designed closed ring resonators with a transverse gradient of surface impedance. The ring resonators provide a wide range of control for the reflection phase with small absorption losses, enabling efficient phase manipulation along the edge of the bump. Our numerical results demonstrate a good performance of the designed cloak in both near field and far field, and the cloaked object mimics a flat ground plane within a broad range of incidence angles, over 35° angular spectrum centered at 45°. The presented cloak design can be applied in radar and antenna systems as a thin, lightweight, and easy to fabricate solution for radio and THz frequencies.