Universal calibration method for microwave moisture sensing in granular materials

A feasibility study of a universal calibration method for nondestructive re al-time sensing of moisture content in granular materials is described. The principle is based on measurement of the dielectric properties of granular materials at microwave frequencies and the use of a calibration function t hat is expressed in terms of these properties to predict moisture content f rom a single moisture calibration equation. Effectiveness of this method is shown for three granular materials exhibiting significant structural and c ompositional differences: wheat, oats, and soybeans. The resulting single m oisture calibration equation, based on measurements of the dielectric prope rties at 9.46 GHz and 24 degreesC, provides moisture content in all three m aterials with a standard error of calibration of 0.46% moisture content, we t basis.