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
Dual frequency microstrip antenna with V slot
A dual-frequency (C- and X- band) microstrip antenna is proposed and the simulation results of its performance are reported. The antenna unit can be incorporated into arrays, and offer the possibility of a compact, light-weight and cost effective antenna array design for various applications such as television broadcasting, wireless communications and radar systems.
Neutron Residual Stress Measurements on Rail Sections for Different Production Conditions
Rail sectioning with subsequent neutron diffraction experiments has been used to assess residual stresses in the rails. In this study we present the results of neutron stress measurements performed at the NIST Center for Neutron Research (NCNR) on rail sections from rails that were produced under various conditions. Specifically, these are air-cooled, air-cooled and roller-straightened, head-hardened and head-hardened and roller-straightened. More significantly, a head-hardened and roller-straightened rail was also studied after service to elucidate evolution of the service-induced residual stresses. In the latter case both a transverse-cut slice and the central region of a 0.53 m long piece were studied. Measurements on this piece are the first in which triaxial stresses have been determined for an intact rail. Neutron strain measurements with 3×3×3 mm3 spatial resolution were successfully employed for transversally cut slices to verify the difference in the stress state depending on the production process. Although examination of slices allows determination of only two-dimensional stresses in the plane of the slice, additional measurements on obliquely-cut slices, which were also carried out, and utilization of FEM gives the possibility of reconstructing the full triaxial stress distribution. Together, these approaches provide a better understanding of rail fabrication and the possibility of improving the durability and safety of rails in the future.Copyright © 2004 by ASME