Determining physical properties of grain by microwave permittivity measurements

Potential use of the complex permittivity measured at microwave frequencies for indirect nondestructive determination of physical properties of grain is discussed. Examples of extraction of bulk density and moisture content f rom permittivity measurements are shown for wheat and corn over wide ranges of frequency and temperature. Calibration equations for both entities are given along with their standard errors of performance (SEP). The bulk densi ty of wheat and corn, ranging from 720 to 880 kg/m(3) and 695 to 830 kg/m(3 ), respectively, can be determined without prior knowledge of the sample mo isture content or its temperature with, on average, SEP of 7.8 kg/m(3) and 12.9 kg/m(3), respectively. The moisture content of wheat and corn, ranging from 10.6 to 19.2% and 9.0 to 19.2%, wet basis, respectively, can be deter mined at a given temperature independent of density with SEP of less then 0 .27% and 0.46%, respectively. One of the attractive features of permittivit y-based methods is that they can be applied regardless of the measurement t echnique. One identified function of the complex permittivity provides mois ture content for both wheat and corn with the same calibration.