  Citation: Ajewole, B.; Kumar, P.; Afullo, T. I-Shaped Metamaterial Using SRR for Multi-Band Wireless Communication. Crystals 2022, 12, 559. https://doi.org/10.3390/ cryst12040559 Academic Editors: George Kenanakis and Luis M. Garcia-Raffi Received: 15 March 2022 Accepted: 13 April 2022 Published: 16 April 2022 Publisher’s Note: MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affil- iations. Copyright: © 2022 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/). crystals Article I-Shaped Metamaterial Using SRR for Multi-Band Wireless Communication Bukola Ajewole *, Pradeep Kumar * and Thomas Afullo Discipline of Electrical, Electronic and Computer Engineering, School of Engineering, University of Kwazulu-Natal, Durban 4041, South Africa; afullot@ukzn.ac.za * Correspondence: ajewolebukolad@gmail.com (B.A.); pkumar_123@yahoo.com (P.K.) Abstract: A novel I-shaped metamaterial (ISMeTM) using split-ring resonator (SRR) for multi-band wireless communication is presented in this paper. The proposed ISMeTM unit cell structure is designed using the three-square split-ring resonators (SSRRs) and I-shaped copper strip at the center. The size of the proposed ISMeTM is 10 × 10 × 1.6 mm 3 while utilizing the FR-4 dielectric substrate material. The analysis of various array arrangements, variation in the ring gap, variation in strip length, and the variation in strip width is performed to achieve the optimum results for multi-band operation. The effective permittivity, permeability, and refractive index of the unit cell have been analyzed. The design and simulation of the ISMeTM unit cell and arrays are performed using the Computer Simulation Technology (CST) Studio Suite and MATLAB. The equivalent circuit of the ISMeTM is designed using the Advanced Design System (ADS) software. The split ring’s inner loop’s gap functions as a capacitor, while the metallic ring itself functions as an inductor. Electric resonance is created by the interaction between the split ring and the electric field. The interaction of magnetic fields with metallic loops during EM propagation in the structure causes the magnetic resonance. The variation in dimensions of the structure causes the variation in the inductance and capacitance, which causes the variation in resonant frequency. The proposed design is optimized after several parametric analyses. A comprehensive analysis of 1 × 2, 2 × 2, and 2 × 4 array is also investigated. The results confirm the multi-band operation of the proposed ISMeTM. The proposed ISMeTM is suitable for the multi-band C/X/Ku-band microwave applications. Keywords: metamaterial; SSRR; permittivity; permeability; multi-band; C-band; X-band; Ku-band 1. Introduction The demand for multi-band operational metamaterials (MeTMs) has increased sub- stantially because of the rapid growth of wireless communication applications. MeTMs are artificially engineered structures which have distinct electromagnetic properties not found in regular materials [1]. Certain materials display negative permittivity and permeability which are not present in nature. In 1945 and 1968, Mandel’shtam and Veselago proposed the concepts the Left Hand Medium (LHM) materials which exhibited negative permittivity and permeability [2,3]. They also presented the general properties of electromagnetic wave propagation in such materials. A metallic structure with negative permeability was presented by Pendry et al. [4] in 1996. He, in collaboration with other researchers [5], also created metallic SRR which is a non-magnetic structure. Furthermore, in 2000, Smith et al. [6] designed the SRR, proposed by Pendry, on a printed circuit board (PCB) by integrating the SRR with set of copper strips. The electric permittivity (ε) and the magnetic permeability (μ) were extracted and analyzed. Transmission-line-based MeTMs was proposed in by Iyek et al. [7] and Caloz et al. [8]. As a result of their distinct electromagnetic characteristics, numerous researchers have proposed and presented several MeTMs for various uses. The application areas of MeTM include design of electromagnetic absorbers [9], multi-band elements [10], Crystals 2022, 12, 559. https://doi.org/10.3390/cryst12040559 https://www.mdpi.com/journal/crystals