Effect of Soil Composition on Complex Dielectric Properties.
Abstract
An industry-standard vector network analyzer system was used to measure the complex reflection and transmission coefficients of 12 different fine-grained soils over a frequency range of 45 MHz to 26.5 GHz. Measurement variables included sample temperature (10, 20, 30, and 40 C), the amount of distilled, deionized water added to each soil sample, and the dry density of the soil in each sample holder (an uncontrolled parameter because of the sample preparation procedure). Data are presented both as a function of frequency at fixed temperatures and moisture content and as a function of moisture content at fixed temperatures and frequencies. Complex results are expressed in numerous ways, including the real and imaginary parts of the complex relative dielectric constant, loss tangent, electrical conductivity (through its relationship to the imaginary part of the dielectric constant), phase velocity normalized to the speed of light in a vacuum, and power attenuation in decibels/meter. Data support earlier models of a critical moisture content. Furthermore, for all but the very lowest frequencies, the data demonstrate that the permittivity of the soils, when considered as a function of volumetric moisture content, can be viewed as independent of soil type. Low-frequency losses in the soil/water/air mixtures are attributed to Maxwell-Wagner effects and ionic conductivity. Soils containing expandable clays demonstrate losses due to bound water of hydration. High-frequency losses are the result of free water molecular dipole relaxation. While both bilinear and least-square polynomial fits to permittivity data for all soil types at selected frequencies are quite acceptable, exponential models do not fit the data well. (MM)
Document Details
- Document Type
- Technical Report
- Publication Date
- Dec 01, 1995
- Accession Number
- ADA304706
Entities
People
- Charles A. Weiss Jr.
- Joel B. Everett
- John O. Curtis