Some Investigations on Metasurface Based Microwave Absorber and their Applications

Abstract

The available materials demonstrate only a small portion of Electromagnetic properties that are theoretically discussed and studied. Initially, J. C. Bose realised and emphasised the possibility of artificial material by arranging twisted structures such materials with meta properties were given the term Metamaterial . The metamaterial are engineered materials which are developed artificially. The artificially design metamaterial provides negative permeability and negative permittivity which result in found its usage in many engineering applications one of such application is metamaterial absorber. In 2004, researcher Smith and his team realised the significance of Metamaterial in various applications. Soon after, researcher Landy and his group provided the information about metamaterial based microwave absorber, the work mentioned was notified with special term Prefect metamaterial absorber . The work formed a base on which latter researchers and scientists experimentally demonstrated and applied Absorption principle in various reported work. When an electromagnetic wave is incident at the boundary interface of two regions then some part of the wave is reflected back in first region, some part gets transmitted in the second region and the remaining part gets absorbed provided no scattering and/or diffraction is occurred. The waves which get absorbed in the material if effective properties like permittivity and permeability are tailored to needs, resulting the absorption of the wave at a particular band. The optimization of physical parameters of metallic layer, thickness of dielectric substrate etc. led to coupling of Electric and magnetic fields to specific input impedance and this input impedance can further be matched to free space impedance for maximum absorption. This complete absorption of electromagnetic wave is realised by minimisation of reflection coefficient. This properties can be utilized for various strategic and important engineering applications. The need of low profile absorber in microwave frequency range results in motivation towards metamaterial absorbers for applications demanding isolation in engineering applications. The thesis work was cantered on the attainment of two objectives, the first being design, development, and characterization of the multiband and wideband absorber and the second one is the application part involving the designed absorber in attaining isolation for MIMO setup. The work completed in various stages is summarized as follows; a. The design of first structure in multiband category focusses on the attainment of multiband absorption with the design and development of a metasurface-based microwave absorber having polarisation insensitivity, broad angle of incidence, low profile, and compactness in the microwave frequency range. b. The second structure focuses on the design of super compact polarization insensitive with wide angular stability, ultrathin triple-band metamaterial absorber. The unit cell comprising patches achieves almost perfect absorption (close to 100%) at C-, X-, and Ku-bands. c. The third structure is a wideband absorber designed and developed with the attainment of more than 99% absorption for ultra-wideband covering a bandwidth of 8.23 GHz from 11.17 GHz to 19.40 GHz. The structure exhibits polarization insensitive behaviour with wide angular stability. d. The application part is completed with the incorporation of metasurface based absorber as an isolator. The mutual coupling of unwanted fields between MIMO antenna elements acts as a major deterrent to exploiting the optimum performance of the MIMO antenna. The work focus on the design and development of MIMO elements and then incorporation of metasurface-based isolator (acting as absorber) clearly with an intention to provide high order optimum isolation levels between two antenna elements. The work succeeded in incorporating a designed absorber in a practical designed MIMO setup with the attainment of good isolation results. newline