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Title: FREE-SPACE MEASUREMENT OF DIELECTRIC PROPERTIES OF MOIST GRANULAR MATERIALS AT MICROWAVE FREQUENCIES

Author
item Nelson, Stuart
item TRABELSI, SAMIR - UNIV. OF GEORGIA

Submitted to: Instrumentation and Measurement Technology Conference Record
Publication Type: Proceedings
Publication Acceptance Date: 5/1/2003
Publication Date: 5/19/2003
Citation: NELSON, S.O., TRABELSI, S. FREE-SPACE MEASUREMENT OF DIELECTRIC PROPERTIES OF MOIST GRANULAR MATERIALS AT MICROWAVE FREQUENCIES. INSTRUMENTATION AND MEASUREMENT TECHNOLOGY CONFERENCE RECORD. 20th IEEE TECHNOLOGY CONFERENCE, VAIL, COLORADO. 2003. p. 518-523.

Interpretive Summary: Interpretive Summary Free-Space Measurement of Dielectric Properties of Moist Granular Materials at Microwave Frequencies Samir Trabelsi and Stuart O. Nelson Moisture content of cereal grains and oilseeds is the most important factor determining suitability for storage. If these commodities are stored at unsuitably high moisture levels, spoilage by fungi and insects can result in severe losses of economic value. Microwave measurements offer potential for improving the reliability of moisture sensing in on-line applications for grain and seed. These new techniques for more reliable moisture measurement could be applied on combine harvesters and in grain handling, drying and processing equipment. The technique involves the correlation between moisture content of the material and its electrical characteristics known as dielectric properties. Thus, reliable measurement of the dielectric properties of grain and oilseed can result in accurate determination of moisture content. This paper reports methods for highly reliable determination of the microwave dielectric properties of wheat, shelled corn, and soybeans and explains the use of these properties in determining moisture content. It also provides tabulated data on the dielectric properties of these materials at microwave frequencies of 5 to 15 GHz over ranges of moisture content of practical interest. The new technique, when developed for practical use, can provide farmers and those working in the grain handling and processing industries new tools for maintaining grain quality and improving the safety and quality of grain products for consumers.

Technical Abstract: Calibration of dielectric-based sensors for reliable on- line monitoring and control of physical properties of moist granular materials requires accurate permittivity measurement. For this purpose, a free-space transmission technique, in which the main sources of errors were minimized, was used to determine the dielectric properties of three major commodities wheat, shelled corn and soybeans. Data collected at room temperature for different moisture levels and wide bulk density ranges are provided over a broad microwave frequency range. An example of the use of dielectric properties for simultaneous moisture content and bulk density is given. Dielectric properties, adjusted for a medium density value through the use of the Landau and Lifshitz, Looyenga dielectric mixture equation are listed for all three materials.