Digital Metasurface Based on Graphene: An Application to Beam Steering in Terahertz Plasmonic Antennas

• Published in: IEEE transactions on nanotechnology Vol. 18; pp. 734 - 746
• Main Authors: Hosseininejad, Seyed Ehsan, Rouhi, Kasra, Neshat, Mohammad, Cabellos-Aparicio, Albert, Abadal, Sergi, Alarcon, Eduard
• Format: Journal Article
• Language: English
• Published: New York IEEE 2019; The Institute of Electrical and Electronics Engineers, Inc. (IEEE)
• Subjects: Beam steering; Design methodology; digital metasurfaces; Electromagnetic radiation; Encoding; Graphene; Information theory; Mathematical models; Metamaterials; Metasurfaces; plasmonics; Reconfiguration; Terahertz frequencies; Tuning; Unit cell
• ISSN: 1536-125X; 1941-0085
• DOI: 10.1109/TNANO.2019.2923727

Metasurfaces, the two-dimensional counterpart of metamaterials, have caught great attention thanks to their powerful capabilities on manipulation of electromagnetic waves. Recent times have seen the emergence of a variety of metasurfaces exhibiting not only countless functionalities, but also a reconfigurable response. Additionally, digital or coding metasurfaces have revolutionized the field by describing the device as a matrix of discrete building block states, thus drawing clear parallelisms with information theory and opening new ways to model, compose, and (re)program advanced metasurfaces. This paper joins the reconfigurable and digital approaches, and presents a metasurface that leverages the tunability of graphene to perform beam steering at terahertz frequencies. A comprehensive design methodology is presented encompassing technological, unit cell design, digital metamaterial synthesis, and programmability aspects. By setting up and dynamically adjusting a phase gradient along the metasurface plane, the resulting device achieves beam steering at all practical directions. The proposed design is studied through analytical models and validated numerically, showing beam widths and steering errors well below 10° and 5% in most cases. Finally, design guidelines are extracted through a scalability analysis involving the metasurface size and number of unit cell states.