Liquid-Permittivity Measurements Using a Rigorously Modeled Overmoded Cavity Resonator

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 overmoded cavity resonator for liquid-permittivity measurements around 100 GHz. Mode-matching modeling of a four-port inhomogeneous waveguide junction removes the limits imposed by previous methods. A cavity with environmental controls was designed and tested. The parameters estimated from the modeling and measurement inputs are plausible and comparable to the literature.