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 andmoisture content in granular materials. The first calibration method is based on measurement of attenuation and phase shiftthrough a layer of material in free space. The attenuation and phase shift were used to determine simultaneously bulk densityand moisture content, and the attenuation-to-phase ratio was used to determine moisture content independent of bulk densitychanges. For the second calibration method, relationships are established between the dielectric properties and bulk densityand moisture content. The dielectric properties were used to determine simultaneously bulk density and moisture content, anda calibration function, expressed in terms of these properties, was used to determine moisture content independent of bulkdensity. In addition, a complex-plane representation of the dielectric properties provided bulk density independent of temperatureand moisture content. Performance of these calibration methods in predicting bulk density and moisture content wascompared for wheat, corn, and soybeans at 10.0 GHz at room temperature. Bulk density and moisture content calibrationequations are given for each material along with corresponding standard errors of calibration.
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Trabelsi et al. (2004) studied this question.
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