Qualitative Characterization of Granular Materials and Moisture Measurements

This chapter focuses on broadband microwave reflectometry (BMR) applications for monitoring water content (θ) and static electrical conductivity (σ 0) of granular materials, with particular emphasis on applications for soil measurements. First, a TDR-based method for inferring θ from measurements of the apparent dielectric permittivity is presented. This approach, which relies on the individuation of so-called calibration curves, is discussed in detail and the related metrological assessment is provided. Successively, a more accurate method that takes into account the frequency-dependence of the dielectric permittivity of the moistened granular material (considering the permittivity of each single constituent) is presented. This application is also used as test-case for validating an innovative calibration procedure that is particualrly useful when the traditional short-open-load (SOL) calibration cannot be performed. Furthermore, the adoption of antennas in place of the traditional probes is discussed (thus assessing the possibility of guaranteeing a noninvasive approach). Finally, two innovative strategies for enhancing and simplifying TDR-based measurements of static electrical conductivity σ 0 (typically used in soil science) are presented.