Models for the Dielectric Constants of Cereal Grains and Soybeans

The development of mathematical models for predicting the dielectric constants of grain as functions of frequency, moisture content, and bulk density is explained. The models are based on the linearity of the square and cube roots of the dielectric constant with bulk density and on measured dielectric constants of representative grain lots at specific frequencies and moisture contents over wide ranges of each variable. Empirical equations are presented for field corn Zea mays L., hard and soft red winter wheat, Triticum aestivum L., spring and winter barley, Hordeum vulgare L., spring oats, Avena sativa L., winterrye, Secale cereale L., and soybeans, Glycine max (L.). Equations for most of the commodities are valid over the frequency range from 20 to 2450 MHz and moisture-content ranges from about 8 to 25%, wet basis; however, equations for wheat cover the 5 MHz to 12 GHz frequency range and 3 to 24% moisture range. Average errors of prediction over the total ranges of both variables are about 3 to 4%.