Ceramic Electromagnetic Bandgap Structures for Microwave and Millimetre Wave Applications

We have investigated defect resonances in two-dimensional electromagnetic bandgap structures made from sintered alumina ceramics. The particular emphasis of our studies was the analysis of quality factors of different types of defect resonances and the search for novel geometries aiming towards their controlled excitation. For the case of a two-dimensional hexagonal dielectric rod structure we have analysed the quality factors of resonant TM modes in an extended defect. We have identified modes with dielectric filling factor of less than thirty percent indicating the possibility of high Q values. In addition, we have demonstrated a defined excitation of such defect resonances by external waveguides. As a step toward a novel millimetre wave integrated circuit technology, we have demonstrated the defined excitation of 3D confined modes of a line defect in an air-suspended dielectric slab. Our results could pave the way to novel types of integrated millimetre circuits based either on LTCC or high temperature ceramics. Possible future applications are integrated low-phase noise oscillator circuits with potential use for optical communication networks, radar systems and point-to-multipoint communication links. (C) 2003 Elsevier Ltd. All rights reserved

Integrated approach for the development of advanced, coated gas turbine blades

This paper describes a through-process modelling on a microstructural level of the production of a coated turbine blade, including its in-service properties and degradation, accompanied by the actual production and testing of a CMSX-4 single crystal turbine blade dummy. The following steps are dealt with by modelling and experiment: solidification of the blade alloy during casting, microstructural changes during homogenization and aging heat treatments, chemical vapour deposition of an Al2O3 diffusion barrier coating, physical vapour deposition (sputtering) of a (Ni,Co)CrAlY bond coat, atmospheric plasma spraying of an Y2O3 stabilized ZrO2 thermal barrier coating and microstructural changes and development of critical stresses at in-service conditions. This work forms a part of the Collaborative Research Centre 370 (SFB370) "Integrative materials modelling"