materials Article Double-Sided Metasurface Array for a Dual-Band and Polarization-Independent Microwave-Energy-Harvesting System Maged A. Aldhaeebi 1 and Thamer S. Almoneef 2, *   Citation: Aldhaeebi, M.A.; Almoneef, T.S. Double-Sided Metasurface Array for a Dual-Band and Polarization-Independent Microwave-Energy-Harvesting System. Materials 2021, 14, 6242. https://doi.org/10.3390/ma14216242 Academic Editors: George Kenanakis and Pilar Marin Received: 23 August 2021 Accepted: 6 October 2021 Published: 20 October 2021 Publisher’s Note: MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affil- iations. Copyright: © 2021 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https:// creativecommons.org/licenses/by/ 4.0/). 1 Department of Electronics and Communication Engineering, Hadhramout University, Mukalla P.O. Box 50512, Yemen; maged.aldhaeebi@gmail.com 2 Electrical Engineering Department, College of Engineering, Prince Sattam Bin Abdulaziz University, Al-Kharj 11942, Saudi Arabia * Correspondence: t.almoneef@psau.edu.sa Abstract: In this article, we present a simple and novel design of a double-sided metasurface for a dual-band and polarization-independent microwave-energy-harvesting system. The proposed metasurface is constructed from the dual-sided design of 8 × 8 unit cells. Different from the regular dual-band unit cells that contain two loops or multiple shapes of resonators printed in the same layer, the proposed metasurface is based on designing double loops, each combined with two arms of a dipole printed on the top and bottom sides of a single substrate. Thus, the bottom layer is utilized to generate the second frequency band of interest. Three main numerical simulations were conducted to investigate the performance of a single unit cell, a 2 × 2 supercell, and an array of an 8 × 8 metasurface structure. The numerical simulation demonstrated that 98% and 95% of the incident energy is collected at two bands of 1.8 and 6.5 GHz for the proposed harvester. Keywords: metasurface harvester; absorbers; energy harvesting 1. Introduction Recent developments in the field of metamaterials opened the possibility of designing and realising near-unity harvesters, enabling many applications such as portable wire- less sensor networks [1,2], RFIDs [1,3], wireless chargeable devices [1,4], the Internet of Things [5], and biomedical implantable devices [6], to name a few. An antenna and a rectification circuit are considered to be the main components to build a microwave-energy- harvesting and wireless power transfer system (MEHWS). The antenna component is utilized to receive the incident electromagnetic (EM) waves and convert them to AC power. The rectification circuit component, however, is used to convert the received AC power by the antenna part to DC [7]. The total performance of the MEHWS depends on the efficiency of each individual component combined. In order to improve the performance of the antenna part, the antenna should be effectively designed to capture an incident EM wave with different polarizations at various bands of frequencies due to the nature of the incident electromagnetic wave having an unknown polarization and frequency of operation [8,9]. Some studies enhanced the electromagnetic wave absorption performance of dual-band and single-band absorbers by using nanosheets [10,11]. Generally, a metasurface array structure has shown superior performance when com- pared to conventional antenna arrays, such as patch arrays, in developing an MEHWS in terms of higher harvesting efficiency [12–14]. Moreover, designing a metasurface harvester is different from designing an absorber where a metasurface harvester captures electromag- netic energy and dissipates it on a connected load rather than having the absorbed energy be consumed within a lossy substrate [14]. In the literature, developing a dual-band and dual-polarization receiving antenna for an MEHWS based on a metasurface antenna array has been considered a challenging Materials 2021, 14, 6242. https://doi.org/10.3390/ma14216242 https://www.mdpi.com/journal/materials