Microwave techniques to determine the average conductivity of tank pad rubber

The conductivity of the rubber composition used in tank pads is an indication of consistency and quality. Two simple, nondestructive procedures to obtain the approximate average electrical conductivity of rubber at microwave frequencies are investigated. One system involves two horn antennas obliquely angled toward the rubber pad. Conductivity is inferred from measurement of the received power reflected from the rubber as compared to received power from a flat metal conductor. Although the model is mathematically simple, the system is difficult to implement due to the very small power level of the received signal,The other system consists of an open-ended waveguide terminated with a large flange and placed at normal incident flush against the sample. The measured complex reflection coefficient of the rubber at the waveguide aperture is the quantity used to infer conductivity. This system is easier to implement, but interpretation of the measured reflection coefficient is computationally intensive. In addition, the interpreted value of conductivity are very sensitive to phase measurement error