Cavity Resonator for Permittivity Measurements of Liquids at Millimeter-wave Frequencies

Abstract

Permittivity data of liquids is necessary for applications such as dielectric heating, remote sensing, and moisture detection, and is also used for molecular characterization. Dispersive molecular mechanisms occur for field excitations of frequencies mainly above 10 GHz and extending into terahertz and optical frequencies. Around 100 GHz there is less data, due to the frequency limits of microwave and quasi-optical techniques. This work presents an over-moded cavity resonator for liquid permittivity measurements. Novel full-wave modeling of a four-port inhomogeneous waveguide junction removes the limits imposed by previous methods. A cavity with environmental control was designed and tested. The parameters estimated from the modeling and measurement inputs are plausible and comparable to literature. Based on repeatability measurements and a sensitivity analysis, recommendations are made for future cavity designs that will enable permittivity measurements at frequencies previously little measured. i I would foremost like to thank Dr. Scott Barker for his guidance, encouragement, and patience, particularly while I wrestled with the modeling. His observations and advice always helped to keep me afloat. I would also like to thank Dr. Robert Weikle III for providing helpful consultations with the modeling, along with Dr. Brooks Pate, Dr. Tatiana Globus, and Dr. Avik Ghosh for serving on my committee and for their helpful knowledge with regards to spectroscopy and liquid measurement. I also want to thank all of the former and present members of MiRFTech and the FIR lab for all of their thoughtful instruction and advice, as well as crucial camaraderie. In particular, Dr. Lihan Chen was always willing to answer my random questions, Matthew Bauwens was of great help with the block design, and Dr. Alex Arsenovic was influential with the Python programming. Thanks must also go the staff of the ECE department for their aid and friendliness. Much gratitude to my friends Alex, Robert, Nii, and Vishal for fun trips and non sequitur e-mails, all of which never failed to amuse and recharge me. And last but not least, the deepest appreciation to my parents for their eternal love and support. I dedicate this work to them.