CALIBRATION METHODS FOR NONDESTRUCTIVE MICROWAVE SENSING OF MOISTURE CONTENT AND BULK DENSITY OF GRANULAR MATERIALS

摘要

The principles of a nondestructive multiparameter microwave sensor operating at a single frequency are presented. Two calibration methods are reviewed and compared for simultaneous, independent determination of bulk density and moisture content in granular materials. The first calibration method is based on measurement of attenuation and phase shift through a layer of material in free space. The attenuation and phase shift were used to determine simultaneously bulk density and moisture content, and the attenuation-to-phase ratio was used to determine moisture content independent of bulk density changes. For the second calibration method, relationships are established between the dielectric properties and bulk density and moisture content. The dielectric properties were used to determine simultaneously bulk density and moisture content, and a calibration function, expressed in terms of these properties, was used to determine moisture content independent of bulk density. In addition, a complex-plane representation of the dielectric properties provided bulk density independent of temperature and moisture content. Performance of these calibration methods in predicting bulk density and moisture content was compared for wheat, corn, and soybeans at 10.0 GHz at room temperature. Bulk density and moisture content calibration equations are given for each material along with corresponding standard errors of calibration