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