Measurement of sand effective dielectric constant

Abstract

The effects of soil water content on dielectric constant are being examined through experimental time-domain-reflectometry (TDR) and frequency-domain reflectometry (FDR) methods in parallel with electromagnetic simulations. The effective relative permittivity (dielectric constant) of the soil, water, and air mixture is highly dependent on the soil's moisture content. Both TDR and FDR methods are performed on a coaxial transmission line filled with a soil/water/air mixture. Water flowing through the mixture creates an active situation in which the soil/water/air electrical impedance changes over time. The resulting mixture has a heterogeneous water content, creating varying electrical impedance along the length of the coaxial line. The effective dielectric constant is found from the data collected from TDR and FDR measurements, and the values are compared with the predictions by the Hendrickx effective dielectric constant model. The Hendrickx fits within three standard deviations of the mean of the measured dielectric constants. A computer simulation technology (CST) Microwave Studio is used to supplement measured observations of a varying mixture moisture contents in a coaxial cell. Simulations validate that the change in dielectric constant, through the medium (Active Region), is a result of the heterogeneous moisture distribution. Physical measurements and modeling showed that soil moisture content has a significant impact on the resulting dielectric constant. In the coaxial cell device, the moisture migration in the mixture during the testing period results in a heterogeneous moisture system and a temporal dielectric constant. This is especially overstated for high hydraulic conductivity soils such as sand. The tenability of the Hendrickx effective dielectric constant model results in a sufficient representation of the measurements.