Cylindrical Microwave Resonator Sensors for Measuring Materials under Flow

Dissertation for the degree of Doctor of Science in Technology to be presented with due permission for public examination and debate in Auditorium S4 at the Helsinki University of Technology (Espoo, Finland) on the 26 th of May, 2000, at 12 o'clock noon. I wish to express my gratitude to Hans-Olav Hide, Arnstein Wee, and my other colleagues at Multi-Fluid/Roxar, who gave me the opportunity to work with the development of microwave sensors for the oil industry and fuelled my interest by providing research and development challenges, and for many interesting discussions regarding the applications. Especially I am grateful to Årstein Bringsvor, Jörn Bolstad, Jone Mellemstrand, and Stein Rörtveit, who have participated in the projects in various ways, and to Frode Knudsen, who initially asked the question that ignited the research on sectorial and semisectorial waveguides and their applications. Finally, I wish to express my deep gratitude to my parents Marita and Börje, and my wife Brit and our children Malin and Emil for their support and patience. ABSTRACT In this thesis the various possibilities of implementing microwave sensors for measureing materials flowing in pipes are studied, with special emphasis on full-bore resonator sensors. With such resonator sensors a method to confine the electromagnetic energy in the sensor must be used. Two main principles are studied in detail, the principle of resonance below cutoff , and the design using end grids. The first principle is shown to allow sensors with fairly open, or even completely nonintrusive structures to be designed. The second often involves sectorial or semisectorial structures. The waveguide modes in sectorial and semisectorial waveguides are therefore analyzed. From the analysis of the sectorial waveguides came the idea for a new type of resonator sensor based on the principle of resonance below cutoff , the cylindrical fin resonator sensor (CFR). Various design aspects of this sensor are studied based on calculations, measurements, and simulations using the Hewlett-Packard HFSS software. A sensor suitable for measuring the composition of mixtures of hydrocarbons and water is developed based on the discussion. The sensor has a simple mechanical structure and is less expensive to manufacture than the end grid sensors. Various designs of end grids are compared based on theoretical considerations, simulations, and measurements, and recommendations for optimized designs are given. The ring grid with eight sectors and a ratio of radii of roughly 40% is shown to provide the best isolation for …