Dielectric resonators and applications in electromagnetics

In this thesis, all-dielectric absorber designs based on dielectric resonator (DR) structures and sensor applications, the effects of boundary conditions and excitation signals on the absorption spectrum, and time-varying DR applications have been studied. In the first part of this thesis, all-dielectric absorbers with DRs were designed, and sensor applications were realized using the designed absorber structures. In the first study, a cylindrical DR-based all-dielectric absorber was designed with chemical liquids, and the chemical liquid sensing application was realized by changing the material used as DR. In the second study, to investigate the effects of DR geometry on sensitivity, the all-dielectric absorber structures were designed using cylindrical, elliptical, square, rectangular, hexagonal, and octagonal DR structures. For each structure, the dielectric constant and loss tangent values of the DR were varied, and the behaviors of the absorption spectrum were investigated. The results show that the shift in the resonance frequency was nearly similar for all DR geometries, and the change in the absorption spectrum with respect to the loss tangent variation was identical. In the third study, to investigate the effects of absorption mode on the sensitivity, elliptical DR-based all-dielectric absorber structures having dipole and quadrupole absorption modes were designed, and sensitivity analyses were performed by varying the dielectric constant and loss tangent values of DRs. The results showed that the amount of shift in the resonance frequency for the quadrupole absorption mode was larger and the change in the absorption peak level with the variation of the loss tangent was smaller. In the fourth study, an all-dielectric absorber was designed with a cylindrical DR, and by loading analyte material around the DR, chemical liquid sensing application and concentration sensing application of ethanol-water mixture were realized. In this study, a sensor design for materials with dielectric constant ranging from 1 to 81 and loss tangent ranging from 0 to 1 was proposed. The simulation and experiment results were in good agreement. In the last study, an all-dielectric absorber was designed with an elliptical DR and moisture sensing applications of grounded coffee and soil, and sensing application of salinity in water was realized by loading analyte material around the DR. In this study, we aimed to design a sensor with higher sensitivity by increasing the amount of analyte material loaded around the DR. From the results, it was evaluated that the sensitivity increases with the increase in the amount of analyte material, and thus the designed structure could be used for moisture sensing applications where the change in the dielectric constant was less. In the second part of this thesis, the effect of boundary conditions and excitation signals on the absorption spectrum of all-dielectric absorber structures was investigated. Since all simulations and experiments were performed with a waveguide setup, the absorption behavior of the designed absorber structures under free space setup was investigated. In the first study, simulations were performed for a cylindrical DR-based all-dielectric absorber structure under a free-space setup. When the obtained absorption spectra were analyzed, it was observed that the absorption modes were separated. It was evaluated that this may be due to the differences in wavelength and wave impedance between the waveguide medium and the free-space medium. The change according to the DR geometry was analyzed in the second study. In this study, simulations were performed for cylindrical, elliptical, square, rectangular, rectangular, hexagonal, and octagonal DR-based absorber structures under free-space setup. It was observed that the behavior was similar for DRs with different geometries. Finally, the change according to the absorption mode was analyzed. In this study, free-space simulations were performed for all-dielectric absorber structures with dipole and quadrupole absorption modes. Separation of absorption modes was observed for the dipole absorption mode, while for the quadrupole absorption mode, no significant separation of absorption modes was observed. In the last part of this thesis, time-varying DR applications were realized. Within the scope of this study, two different applications were made. In the first application, the effects of the amount of time-varying material on the resonance characteristics were investigated. In this context, cylindrical DRs were designed with chemical liquids that can evaporate at room temperature and excited with a microstrip transmission line. It was observed that as the chemical liquid evaporates over time, the resonance characteristic changes due to the change in the height of the DR. In the second application, the effects of time-varying temperature on the resonance characteristics were investigated. In this study, a cylindrical DR was designed with deionized water whose electrical permittivity values change with the temperature change and excited with a microstrip line. It was observed that the resonance characteristic changed with the change in the water temperature. From the results obtained, it is believed that the studies carried out within the scope of this thesis will make an important contribution to the related literature.