Seawater dielectric measurement by using a cavity technique: Exit-hole effect analysis

The resonant cavity technique is considered as one of the most accurate methods for determining dielectric constants of liquids. Using this technique, the sample is introduced into the cavity through a hole in a glass tube centered on the cavity's axis. The glass tube enters and leaves the cavity through a small hole in each end plate. These exit-holes have an effect on the electromagnetic fields inside the cavity and change its resonant frequency. The effect of these exit-holes has concerned investigators for years. In this paper, the exit-hole effect has been analyzed using waveguide theory. Higher order modes have been taken into account to increase the accuracy of the method. In addition, a special experimental setup has been designed to validate this theory.