In Situ Microwave Measurements of Dielectric Properties and Moisture in Materials

摘要

The accurate nondestructive evaluation of dielectric properties of materials is important for quality control, safety, liability, and economic reasons. A significant problem is the determination of water content in low-loss dielectric materials, since the presence of water will notably alter the value of the materials' permittivity and physical properties. An open-ended coaxial resonator incorporated in a microwave homodyne detection system may be used to measure changes in its resonant frequency and quality factor resulting from changes in permittivity and hence water content. This paper describes such a system and presents results that prove it is capable of measuring water content in reference samples to less than 100 parts per million (ppM). System improvements are also described which will result in measurement accuracies of less than 50 ppM water in low-loss dielectric materials. (ERA citation 10:019030)