Dielectric properties of soils at UHF and microwave frequencies

The complex dielectric constant of four soils, including a sand, a silt, and two clays, was measured over the frequency range from 0.1 × 109 Hz to 26 × 109 Hz. The water content of the soils was varied from 0.0 g H2O/g soil to 0.15 g H2O/g soil, and the temperature from 24°C to 20°C. The dielectric relaxation spectrum of water in soils was found to be displaced to lower frequencies than the dielectric relaxation spectrum of water in bulk. The results showed that the relation between volumetric water content and the complex dielectric constant is relatively independent of soil type. At temperatures above freezing the complex dielectric constant of water in soils, at the water contents investigated, decreases with temperature, a type of behavior normally found only in solids. Below the freezing point the phase composition of water in soils determines the temperature dependence of the complex dielectric constant.