Abstract:
This thesis presents analytical and numerical studies on the effects of shapes and permittivities of embedded defects in epsilon-near-zero (ENZ) metamaterials based waveguides on their electromagnetic wave propagation characteristics. These studies enable new methods for controlling transmission, reflection, focusing and filtering of electromagnetic waves through these devices. Firstly, an isotropic ENZ metamaterial-based waveguide embedded with rectangular defects is investigated in the microwave regime. It is found that its transmission coefficient can be adjusted over 90 percent simply by adjusting the permittivity of the defect over a wide range, like 1.5 to 2.5 and even total transmission can be achieved. It is seen that the transmission co-efficient of the waveguide goes to zero and then to one for a very small change of defect permittivity. The characteristics can be improved by introducing a rectangular and a circular defects together. This particular structure, combining both rectangular and circular defects, also appears to be useful as a tunable filter. The operating frequencies of the filter are found to be tunable by varying the defect geometries and their permittivities. A frequency selector built by a rectangular defect at the ENZ medium has also been studied. Analytical expressions for the transmission co-efficient of such devices with a single rectangular defect and a combination of rectangular and circular defects have been derived. It is found that better tuning of transmission co-efficient (above 90 percent) is possible for structures with combination of defect shapes. The propagation characteristics are also obtained by solving the Maxwell's equations numerically. The analytical expressions are thus validated, and the developed analytical equations can provide a valuable design insights for the metamaterial based guiding structures that include defects in them.
