979-8-3503-3412-8/23/$31.00 ©2023 A Review on Electromagnetic Metamaterial Absorbers Jeena Viji Department of Electronics and Communication Engineering College of Engineering, Trivandrum Kerala, India jeenaviji@gmail.com Titto Anujan Department of Electronics and Communication Engineering College of Engineering, Trivandrum Kerala, India titto@cet.ac.in Abstract— Metamaterials are artificially engineered materials that possess properties that are not present naturally. They show some specific properties such as negative refractive index, negative permittivity, negative permeability and left hand behavior. Metamaterial absorbers have greater attention in nowadays because of its ability to absorb incident electromagnetic radiation. The structure consists of resonator layer, dielectric substrate and metallic ground plane. They are applicable in radar cross section reduction (RCS), energy harvesting, electromagnetic shielding and refractive index sensing. In this paper, various metamaterial absorbers and their applications are reviewed. Initially the theory and working of metamaterial absorbers are discussed. Several multiband absorbers and their absorptivity are then presented. Next, the review focuses on several broadband absorbers and polarization insensitive absorbers. By using these metamaterial absorbers, we can make near-unity absorption. Keywords— Metamaterial absorbers, multiband, broadband, polarization. I. INTRODUCTION Metamaterials are artificial composite structures or composite materials with supernormal physical properties, according to the concept put forth by Walse. The artificial structure, not the material itself, is what gives metamaterials their exceptional performance. Metamaterials defy conventional design concepts and achieve exceptional attributes through the design of organized structures at a physical scale. The remarkable performance of metamaterial has garnered interest from a variety of fields, resulting in more extensive applications such as, perfect metamaterial absorbers, zero index materials, invisible cloaks etc. Electromagnetic radiation and pollution have gotten much worse with the advancement of electronic devices and communication technology. Stealth technology, electromagnetic compatibility and electromagnetic radiation pollution can all be solved with the use of potential applications in energy collecting, sensing and detection. Higher requirements for absorbers have been introduced due to the presence of EM sources. Metamaterial absorber is a type of frequency selective surface which can trap the incident electromagnetic radiation with near-unity absorbance. The mechanism of metamaterial absorber is similar to that of band stop filter. Because the electromagnetic waves incidenting on its surface are neither reflected nor transmitted through the structure at the resonant frequency. Zero transmission is achieved by using metallic ground plane whose thickness is selected larger than the skin depth while zero reflection is accomplished by the impedance matching with free space. The resonance wavelength thickness of functional layers significantly thinner than their counterparts can be around 25 times less than the thickness of a metamaterial perfect absorber. This paper presents a review on various kinds of metamaterial absorbers and their applications. Compared with the conventional absorbers such as Salisbury screen and Jaumann absorber [1], metamaterial absorber has light weight, low cost and near-unity absorbance. Radar cross section reduction (RCS) [2], energy harvesting [3], electromagnetic shielding [4] and refractive index sensing [5] are some of the applications of the absorber. The structure of metamaterial absorber is similar to a sandwich model with 3 layers- top resonator layer, bottom ground plane and a dielectric substrate in the middle [6]. The very first metamaterial absorber was designed by Landy in 2008[7]. The designed structure operates only in single band frequency (11.5GHz) with 88% absorptivity. So there is a need for designing multiband metamaterial absorbers with greater absorptivity. Applications like multiband sensing are made possible by multi-band metamaterial absorbers, which provide perfect absorption at a number of distinct frequencies. Dual band and triple band metamaterial absorbers were designed later both in GHz and THz frequency [8]-[11]. Besides multiband metamaterial absorbers, researchers were also focused on broadband metamaterial absorbers [12]-[13]. Later they focused on polarization insensitivity and designed multiband polarization insensitive absorbers [14]-[15]. II. METAMATERIAL ABSORBERS A. Structure and Working The structure of metamaterial absorber consists of top resonator layer, bottom ground plane and a dielectric substrate in the middle [6]. Its working is based on the transmission line theory and loss mechanism. When the electromagnetic waves incident on the resonator layer surface currents are induced which are responsible for the electric response. The resonator layer also relates to the ground, which induces antiparallel currents. These current 2023 International Conference on Control, Communication and Computing (ICCC) 19-21 May 2023 2023 International Conference on Control, Communication and Computing (ICCC) | 979-8-3503-3412-8/23/$31.00 ©2023 IEEE | DOI: 10.1109/ICCC57789.2023.10165509