Factors affecting the complex permittivity spectrum of soil at a low frequency range of 1 kHz-10 MHz

Abstract

To establish the factors affecting the permittivity spectrum of soil in the low frequency range, the complex permittivities of soils were measured at the frequency range of 1 kHz-10 MHz. The effects of frequency, water content, soil types and heavy metal contamination on the dielectric response were evaluated and their theoretical mechanisms were discussed. Measurement distortions such as electrode polarization in the low frequency measurements were identified. The permittivity of the soil was analyzed at frequencies above 100 kHz, which was experimentally determined to be the limiting lower frequency. The real permittivities of the soils were strongly related to the volumetric water content, since it is determined by the polarizability of the free water. The effective imaginary permittivities of soils increased with volumetric water content due to the increase in conduction losses. The spatial polarization and conduction loss were found to be the main mechanism in the real and effective imaginary permittivity, respectively. Since such mechanisms are influenced by the specific surface area of the soil particles, the presence of particles with high specific surface area in the soil matrix was found to affect the permittivity of soil. Contamination of saturated soil by cationic species resulted in decreases in the real permittivity due to the decreased orientation polarization of water molecules caused by hydration of ions, but increases in the effective imaginary permittivity due to ionic conduction.