18 Microwave Properties of Dielectric Materials
In recent years, the study of newer types of dielectric materials and compositions has been of great interest. The quest for new, innovative and easily obtainable dielectric materials that yield predictable and controllable permittivity and permeability values with very low dielectric loss has always been fruitful. New ideas and designs to implement these materials in microwave devices and structures with the most efficiency and performance are also of equal importance. The book chapter covers the synthesis and characterization of new dielectric material compositions and the design, implementation and testing of a prototype dielectric resonator antenna and filter utilizing the fabricated dielectric material. It also covers the use of different design and testing techniques in this research. By studying different methodologies and new material types that were previously published in cited technical journals such as Science Direct, different types of materials and synthesis methods were able to be identified. The appropriate materials and method of synthesis were then derived and utilized in the fabrication of the new type of dielectric ceramic substrate material. After extensive literature reviews, research and analysis, various methods used in dielectric resonator designs were studied and analyzed. An overview of the synthesis process associated with the fabrication of the new dielectric composition will be discussed. Next, with the primary objective of investigating the microwave properties of a new composition of high permittivity ceramic dielectric substrate at microwave frequencies, research is then carried out on designing an electrical model in order to utilize the newly fabricated dielectric material in a microwave environment. The electrical model that is proposed will be of dielectric resonator devices which will incorporate the new dielectric material type. Tests and measurements will also be carried out at various microwave frequencies in order
Electromagnetic Scattering by Mixed Conducting/Dielectric Objects Using Higher-Order MoM
In this paper, the higher order hierarchical basis functions are employed to solve the electric field integral equation for computing electromagnetic scattering from three-dimension bodies comprising both conducting and dielectric objects. In higher-order methods of moments (HO-MoM), the equivalent surface electric and magnetic currents are usually expanded by the same basis functions, which are not appropriate in our problem here. The pointwise orthogonal basis functions respectively for electric and magnetic currents are proposed in our improved HO-MoM. Quadrilateral patches are used in curvilinear geometry modeling since they result in the lowest number of unknowns. Numerical solution procedure is particularly analyzed, and numerical results are given for various structures and compared with other available data lastly.
SR topography of plastically deformed Fe-Si bicrystals - observation in situ and post mortem
SR reflection topography was applied to study the interaction of slip dislocations with the grain boundaries in Fe-4at%Si bicrystals deformed by compression. Three experimental settings with either a white or monochromatic beam were used and the corresponding orientation contrast analysed. Dislocation transmission through the grain boundary was observed in bicrystals with favourable geometry of the slip systems.