Abstract
A low-cost microwave sensor for nondestructive, rapid sensing of bulk density and moisture content in grain and seed has been built and tested. The sensor operates at a single frequency of 5.8 GHz and uses the principle of free-space-transmission measurement of the relative complex permittivity. Results of complex permittivity measurements with this sensor compared very well to those taken with a vector network analyzer and a pair of horn-lens antennas. Three different calibration algorithms were used to determine bulk density and moisture content from the two components of the relative complex permittivity. With the first calibration algorithm, bulk density and moisture content were determined simultaneously. The second algorithm allowed bulk density determination without knowledge of moisture content and temperature of the sample from a complex-plane representation. Finally, a unified calibration algorithm was used for moisture determination independent of bulk density and independent of the kind of material. Results of bulk density and moisture content prediction from complex permittivity measurement with a low-cost microwave sensor are reported here for wheat and soybeans.
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