Non-destructive coaxial transmission line measurements for dielectric soil characterization

A high-frequency electromagnetic measurement technique is employed to investigate dielectric properties of a fine-grained soil. As a case study, a standardized compacted fine-grained soil was investigated using a coaxial transmission line cell in combination with vector network analyzer technique in a frequency range from 1 MHz to 3 GHz. The measurement results indicate that this type of sensor enables the broadband determination of soil dielectric spectra, i.e. the frequency dependent relative effective complex permittivity. Hence, with the introduced coaxial transmission line setup the dielectric relaxation behavior of the investigated soil can reliably characterize defined structural states. Moreover, it was found that dielectric material parameters at high frequencies are mainly related to the volume fractions of the soil phases, i.e. water content whereas at low frequencies to soil structure and density due to interface processes.