2008 Volume 110 Pages 13-23
Time domain reflectometry (TDR), measuring dielectric properties, has widely been applied to monitor volumetric water content (θ) and bulk electrical conductivity (σb) in soil. TDR is, however, not applicable to clays due to the inadmissible energy loss of emitted microwave signals. To reveal the response of the clays to the signals, by using a vector network analyzer we measured the spectra of real (ε') and imaginary (ε") part of complex permittivity in the frequency of 0.1 to 3.0 GHz for kaolinite and bentonite having di erentθ-values. Besides the distinctε"- and ε"-spectra for θ, for kaolinite we found that the relation of ε' versus θ can be given by a unique expression within a range of examined frequency, and can be estimated from ε" -values at around 3.0 GHz with relatively small errors. Although the σb values for the bentonite, estimated by the present method, included unacceptable large errors, the relations of ε' versus θ were adequately determined in whole examined frequencies. Judging from the gradient of ε' - θ relations for bentonite, we suggested that the signals with higher frequency should provide more sensitive determination of than θ that with lower frequencies.
