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Title: MICROWAVE MOISTURE SENSING IN CEREAL GRAINS AND OILSEEDS

Author
item Nelson, Stuart
item TRABELSI, SAMIR - UNIVERSITY OF GEORGIA

Submitted to: Microwave Power Symposium Proceedings
Publication Type: Proceedings
Publication Acceptance Date: 5/13/2005
Publication Date: 7/12/2005
Citation: Nelson, S.O., Trabelsi, S. 2005. Microwave moisture sensing in cereal grains and oilseeds. In: Proceedings of the 39th Annual Microwave Symposium, July 13-16, Seattle, WA, p. 101-104.

Interpretive Summary: Moisture content is the most important characteristic of cereal grains and oilseeds affecting their suitability for harvesting, storage, transport, and processing. It is also an important factor affecting the price paid for the commodity. Therefore, moisture content must be determined whenever grains and oilseeds are traded. If moisture content is too high at time of harvest, the grain kernels can be damaged in the mechanical harvesting process, leaving them more susceptible to infection by fungi. If they are stored at moisture contents too high for the prevailing environment, they can spoil because of the action of microorganisms, and the value is degraded or completely lost for human and animal consumption. Electronic moisture meters have been developed and used for many years to provide quick moisture determinations. However, instruments to monitor grain moisture content in moving grain for on-line applications have not been entirely satisfactory, because changes in the grain packing or grain temperature can give large errors in moisture content. Research on microwave measurements for sensing grain moisture content has provided means for determining moisture content independent of changes in packing and compensated for grain temperature. The general principles involved in using microwave measurements for sensing grain moisture are presented in this paper. The technique is illustrated with data on the microwave dielectric properties (electrical characteristics) of wheat, and it is shown that moisture content can be reliably sensed through measurement of these dielectric properties and use of moisture calibration equations that depend only on the dielectric properties. Thus, the measurement is independent of bulk density of the grain (degree of packing) and it can be compensated for variations in grain temperature. Further, research with corn, wheat, soybeans and oats has shown that a single moisture calibration equation works well for all grains, promising a universal calibration, which should encourage the commercial development of the technique for practical use.

Technical Abstract: The importance of moisture content in cereal grain and oilseed and principles for sensing moisture content by microwave measurements on such granular materials are discussed. Transmission measurements of attenuation and phase shift as the wave traverses a layer of material provides the information necessary to determine the dielectric properties, and from these properties the moisture content and bulk density can be determined independent of each other. A universal moisture calibration appears possible for grain and seed.