Extracting Soil Permittivity Using Uncalibrated, Thickness and Position-Independent Hollow Coaxial-Probe Techniques

Accurate soil-moisture content measurement is crucial for agricultural productivity and environmental monitoring, driving extensive research into measurement techniques that are both precise and adaptable to varying soil conditions. Among the various methods, microwave-based sensing methods have garnered research interest owing to their high sensitivity and contactless sensing, but require frequent calibration and precise information on the position and thickness of the soil samples. This work presents and investigates a mathematical framework for the accurate determination of the dielectric permittivity using a hollow coaxial line for the calibration-free position-independent measurement of soil moisture content. The presented framework utilizes a mathematical model consisting of wave-cascading-matrix presentation to eliminate the thickness-, position-, and calibration-dependencies of a typical hollow coaxial line. The developed method is validated by dielectric permittivity measurement of both solid and granular soil samples with different conductivities and moisture content, post which calibration curve models are plotted. The curve models are compared with other similar models created through existing methods for accuracy analysis. The developed method can find applications in agriculture, environmental monitoring, and civil engineering, where accurate characterization and monitoring and adaptability to varying soil conditions are critical for effective decision-making and resource management.