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Soil Dielectric Spectra from Vector Network Analyzer Data

National Soil Tilth Lab., 2150 Pammel Dr., Ames, IA 50011

View larger version (15K): [in a new window]   Fig. 1. Dielectric spectra and Cole–Cole plots for water at 25°C.

View larger version (20K): [in a new window]   Fig. 2. Truncated coaxial sample holder used in this study.

View larger version (12K): [in a new window]   Fig. 3. The electrical sample length, determined as the slope of 2c/(4f1) as a function of expected a1/2 (square root of apparent permittivity), in which c is the speed of light and f1 is the measured frequency of the first minimum in the real scattering parameter (S11) (quarter wavelength).

View larger version (19K): [in a new window]   Fig. 4. Example spectra of real and imaginary permittivity for Weld soil at water content of 0.346 m3 m–3, after subtracting the electrical conductivity component from the imaginary permittivity. The hf is the real permittivity at the high frequency limit. The = is the component due to electrical conductivity.

View larger version (17K): [in a new window]   Fig. 5. Example resistivity spectra and Cole–Cole plots derived from the sample permittivity data (Weld at water content of 0.346 m3 m–3).

View larger version (32K): [in a new window]   Fig. 6. Example permittivity spectra at the lowest water content, with hygroscopic (bw) and free (fw) water contents given for the duplicate samples (separated by comma) of each soil. The Weld and Okoboji soils indicate a relaxation (bulge) within the measured frequency range (indicated by arrows).

View larger version (21K): [in a new window]   Fig. 7. Effect of water content and electrical conductivity on the real and imaginary components of permittivity (relaxation and electrical conductivity contributions) at 10 MHz.