A Complex Permittivity Measurement System for Undisturbed/Compacted Soils

The design and calibration of a complex permittivity measurement device for undisturbed and compacted soils is presented. The system consists of an automatic network analyzer, a sample holder, coaxial cables, and software to process data. The design of the sample holder and the limitations and sources of errors in the measurement system are discussed. The complex permittivities of two natural clayey soils were measured over the frequency range of 0.3 MHz to 1.3 GHz. For the soils tested, the dielectric constants and volumetric water contents showed a linear trend that was independent of the soil type. It was found that when performing the complex permittivity measurements the soil specimen length should be kept constant and as short as possible while ensuring that the sample is representative of the in-situ soil fabric and grain-size distribution.