The Effect of Dielectric Relaxation Processes on the Complex Dielectric Permittivity of Soils at Frequencies From 10 kHz to 8 GHz—Part I: Experimental

This is the first of two articles that present experimental spectra of six soil samples with varying clay contents ranging from 0 to 55% and organic carbon levels ranging from 0 to 3.9%, measured at a small step of moisture change at a temperature of 25°C. The study was carried out using a method that enables measurements of the same sample over a wide frequency range of 1 kHz to 8.5 GHz, and in some cases up to 20 GHz. The relative effective complex dielectric permittivity (RCP) is strongly influenced by dielectric relaxation processes due to the Maxwell-Wagner effect in the frequency range of 10 kHz to 8.5 GHz, as demonstrated. These processes are aided by the presence of clay in the soil. Up to frequencies of 4-5 GHz, these processes have a weak influence, mainly on the imaginary part of the RCP. This explains why in the dielectric models of Dobson and Mironov, where relaxation processes are ignored, free and physical bound water have high specific conductivity. We demonstrated that organic carbon, even at low content, reduces the real and imaginary parts of the RCP when all other factors are equal. Part II will present the results of using the Debye and Cole-Cole formulas to model relaxation processes.