Effects of "Natural" Water and "Added" Water on Microwave Dielectric Properties of Shelled Corn at Microwave Frequencies

Authors: Trabelsi, Samir; Nelson, Stuart; Lewis, Micah

Submitted to: Journal of Microwave Power and Electromagnetic Energy
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/8/2009
Publication Date: 7/8/2009
Citation: Trabelsi, S., Nelson, S.O., Lewis, M.A. 2009. Effects of "Natural" Water and "Added" Water on Microwave Dielectric Properties of Shelled Corn at Microwave Frequencies. Journal of Microwave Power and Electromagnetic Energy.

Interpretive Summary: The electrical characteristics of grain known as dielectric properties are used by electronic grain moisture meters for rapid determination of moisture content. Moisture content is important in determining the potential for safe storage of grain, and it must be measured whenever a grain lot is sold. Recent research has shown that measurements on grain at microwave frequencies offer advantages for moisture testing compared to the lower radio frequencies currently used by commercial grain moisture meters. This research has also shown that the moisture content of grain can be rapidly obtained from microwave measurements that determine the dielectric properties of the grain independent of fluctuations in the bulk density (packing) of the grain, which causes errors in the moisture content indicated by currently used moisture meters if it is not taken into account. Therefore the microwave sensing of grain moisture content shows promise for on-line monitoring of moisture in grain and seed. Questions have been raised as to whether dielectric properties of grain of high moisture contents at harvest are different from those of the same grain to which water has been added, after drying, to bring it back to the original moisture level. In this study, microwave dielectric properties of shelled, yellow-dent hybrid field corn were measured at harvest and as the corn dried down to normal storage levels. Then, water was added to hybrid corn lots of normal storage moisture levels and the dielectric properties were measured as moisture content was increased to levels for corn at harvest. Comparing results of the measurements showed that there was no appreciable difference between the natural-moisture and added moisture-lots of shelled corn. Thus, the customary method for adding moisture in research studies does not introduce any complications in research on microwave methods for sensing moisture content in corn. The new information is useful to engineers developing new moisture meters and it will therefore contribute to the goal of providing high quality and healthful products for consumers.

Technical Abstract: Dielectric properties of samples of shelled corn of “natural” water content and those prepared by adding water were measured in free space at microwave frequencies and 23 oC. Results of measurements of attenuation, phase shift and dielectric constant and loss factor at 6 GHz show no difference between the samples with “natural” water and those in which water was added artificially. Also b ulk densities and moisture contents predicted from dielectric properties were good agreement.