Microwave Dielectric Properties of Cereal Grains

Abstract

Dielectric properties of five cereal grains (wheat, corn, barley, oats, and grain sorghum) were measured at 23C over a range of moisture contents and over microwave frequencies from 5 to 15 GHz with a free-space transmission technique. Resulting dielectric constants and loss factors are tabulated for each material for moisture ranges of interest to the grain industry at bulk densities that are close to the corresponding test weight of those cereal grains. Bulk densities of all grain lots decreased linearly with increasing moisture content. Both the dielectric constant and loss factor of all grain lots increased nearly linearly with increasing moisture content at all frequencies. For given moisture contents, the dielectric constants of all grains tested decreased with increasing frequency, and the loss factor changed relatively little over the frequency range. The new data will be useful in grain moisture sensing work and in microwave heating applications.