Abstract
Independent control of electromagnetic (EM) waves by metasurfaces for multiple tasks are highly desired and is the recent hot topic of research. In this work we contribute a polarization insensitive frequency multiplexed 2-bit coding metasurface to control the Terahertz (THz) waves in the two operating bands independently. In this regard, as a first step a cascaded meta-atom composed of square rings and/or square metallic patches separated by two polyimide substrates is designed and optimized that provides sixteen independent distinct discrete phases in the reflection geometry. These meta-atoms are then distributed with distinct coding sequences in the two-dimensional spatial plane to realize various bi-functional metasurfaces. As a proof of the concept various full structures are designed and simulated to realize a series of bi-functionalities including anomalous reflection/beam shaping, beam shaping/anomalous reflection, beam deflection/Orbital angular momentum (OAM) beam generation with distinct modes and propagating wave to surface wave (PW-SW) conversion/PW beam manipulation in the lower and higher THz bands, respectively. All the simulation results are in excellent agreement with their theoretical equivalents. We envision that the proposed meta-designs have potential applications for the multi-spectral control of EM waves in THz band. The idea can be further extended to design frequency dependent tri-functional and multi-functional THz meta-devices.