Novel Multiband and Broadband Metamaterial Absorber for RCS reduction and EM shielding

Abstract

Metasurfaces are artificial structures carefully designed to exhibit extraordinary characteristics, including the ability to exhibit negative refractive index, negative permittivity, and negative permeability as well, which are unattainable in naturally occurring materials. These subwavelength designs have found extensive applications and offer enhanced efficiency in various fields, including solar energy harvesting, electromagnetic (EM) shielding, beam splitting, and more. Although classical techniques like the Faraday effect and bi-refringence can achieve perfect absorption of EM waves, they often come with drawbacks such as increased costs, design complexity, structural non-linearities, and bulkiness. Consequently, metasurface-based perfect absorbers have earned significant interest among researchers over the past two decades and continue to be actively explored. Perfect absorption can be achieved through the design of left-handed metamaterials (LHMs), which reduce losses and provide negative permittivity and permeability. Numerous LHMs have been proposed in the literature; however, many designs lack angular stability and polarization insensitivity. In this thesis, we present three metasurface designs. The first design is a tetra-band metasurface absorber intended for X and Ku band applications. It is based on the concept of Split Ring Resonators (SRRs) and utilizes an FR-4 substrate. The proposed design exhibits four distinct absorption peaks, with polarization insensitivity up to 90˚ and an angular stability of 60˚. Subsequently the 2nd design entails a wideband metamaterial absorber (MA) that proves to be highly suitable for deployment across a diverse range of energy bands, specifically encompassing the C, X, K, and Ku frequencies. The structured MA design incorporates Cyclic-4 (C-4) symmetry, having excellent angular stability and showing excellent response to polarization insensitivity till 90˚, which a huge achievement in case of broad band meta surfaces. The design features a modified square ring-shaped structure implemented on a FR-4 economical substrate, utilizing SMT resistors to achieve a high absorptivity of 99%. The third design is a frequency-tunable metasurface employing resistors, inductors, and diodes. This design enables the metasurface to switch bands from X-band to Ku-band by toggling the diodes on and off. Various parametric analyses and modifications were conducted to optimize absorption. An in-depth analysis of surface current and electric field vii distributions was conducted with the aim of comprehending the intricate absorption mechanisms at play. To evaluate the simulated results the above designs MAs were fabricated, and it has been observed that the simulated and experimental results have shown good agreement with each. The designed meta surfaces have extensive applications related to radar stealth material, energy harvesting, and various microwave applications. It is worth noting that our planar, symmetric, single-layered, and passive-elements-based MA design achieves superior accuracy compared to previous studies.