Dielectric properties of clays in microwave frequency
2008
Miyamoto, H.(Saga Univ. (Japan)) | Shimomachi, T. | Chikushi, J. | Yasunaga, E.
Time domain reflectometry (TDR), measuring dielectric properties, has widely been applied to monitor volumetric water content (theta) and bulk electrical conductivity (sigmasub(b)) 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 (epsilon') and imaginary (epsilon'') part of complex permittivity in the frequency of 0.1 to 3.0 GHz for kaolinite and bentonite having different theta-values. Besides the distinct epsilon''- and epsilon''-spectra for theta, for kaolinite we found that the relation of epsilon' versus theta can be given by a unique expression within a range of examined frequency, and sigmasub(b) can be estimated from epsilon''-values at around 0.3 GHz with relatively small errors. Although the sigmasub(b) values for the bentonite, estimated by the present method, included unacceptable large errors, the relations of epsilon' versus theta were adequately determined in whole examined frequencies. Judging from the gradient of epsilon'-theta relations for bentonite, we suggested that the signals with higher frequency should provide more sensitive determination of theta than that with lower frequencies.
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