Factors affecting the dielectric properties of grain
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ABSTRACT THE influences of various factors that affect the di-electric properties of grain are discussed, based on information in the literature. Moisture content of the grain and frequency of the applied electric field are the two most important factors. Bulk density of the grain and temperature also affect the dielectric properties. The moisture sorption-desorption history of the grain and its chemical composition have lesser influences on the dielectric properties. Nonhomogeneity of the grain as a dielectric can affect the measured dielectric properties when kernel dimensions are an appreciable fraction of the distance between electrodes in the sample holder. The dielectric constant increases with increasing moisture content and decreasing frequency, whereas the loss tangent and loss factor may increase or decrease with changes in these two variables, depending upon the range of each. The dielectric constant has positive bulk-density and temperature coefficients, but the cor-responding coefficients for loss tangent and loss factor may have either sign, depending upon moisture content and frequency. Sources of information on the dielectric properties of grain are identified, and contour plots of the dielectric properties of wheat and corn are presented as functions of frequency and moisture content.