Principles of microwave moisture measurement in grain

The importance of cereal grain moisture content in determining time of harvest and in preserving grain quality is described. Techniques for moisture measurement, including electronic moisture meters, are also discussed briefly, and the need for better moisture sensing techniques for modern agricultural on-line moisture monitoring is described. Principles of microwave free-space measurements involving attenuation and phase determination are explained, and density-independent functions of the grain permittivity are presented that permit reliable moisture sensing applicable to moving grain in which bulk, density variation occurs. A new moisture calibration function, based on complex-plane plots of the density-normalized dielectric constant and loss factor, is described, which promises a universal calibration for different types of grain and seed. This important advantage should encourage commercial development for practical use.