Free-space measurement of dielectric properties of cereal grain and oilseed at microwave frequencies

• Published in: Measurement science & technology Vol. 14; no. 5; pp. 589 - 600
• Main Authors: Trabelsi, Samir, Nelson, Stuart O
• Format: Journal Article
• Language: English
• Published: Bristol IOP Publishing 01.05.2003; Institute of Physics
• Subjects: Exact sciences and technology; Infrared, submillimeter wave, microwave and radiowave instruments, equipment and techniques; Instruments, apparatus, components and techniques common to several branches of physics and astronomy; Physics; Submillimeter wave, microwave and radiowave spectrometers; magnetic resonance spectrometers, auxiliary equipment, and techniques; Submillimeter wave, microwave and radiowave spectrometers; magnetic resonance spectrometers, auxiliary equipments and techniques; Sample holders; Error analysis; Oilseed; Permittivity measurement; Dielectric properties; Moisture; Corn; Measuring methods; Dielectric measurement; Soybean; Experimental study; Microwave devices; Wheat; Permittivity
• ISSN: 0957-0233; 1361-6501
• DOI: 10.1088/0957-0233/14/5/308

Principles of dielectric property measurement by microwave free space transmission line measurements are presented and the important sources of errors discussed. A system is described for such measurements that includes a vector network analyser, horn/lens antennas, a holder for grain and oilseed samples, and a radiation absorbing enclosure. The techniques and procedures followed to obtain reliable permittivity data for wheat, shelled corn (maize) and soybeans are outlined. Data illustrating linear relationships between microwave attenuation and phase shift per unit sample thickness, each divided by the bulk density of the granular materials, and frequency and moisture content, are presented graphically. The linear dependence of calculated permittivity components, dielectric constant and loss factor on bulk density is also shown. Permittivity components for wheat, corn and soybeans are listed at frequencies from 5 to 17 GHz at different densities and moisture levels at about 23DGC.