The design and calibration of a complex permittivity measurement device for
undisturbed and compacted soils is presented. The system consists of an au
tomatic network analyzer, a sample holder, coaxial cables, and software to
process data. The design of the sample holder and the limitations and sourc
es of errors in the measurement system are discussed. The complex permittiv
ities 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 vol
umetric water contents showed a linear trend that was independent of the so
il type. It was found that when performing the complex permittivity measure
ments the soil specimen length should be kept constant and as short as poss
ible while ensuring that the sample is representative of the in-situ soil f
abric and grain-size distribution.