Submitted to: Antennas & Propagation Society Symposium Digest Institute Electrical.......
Publication Type: Other
Publication Acceptance Date: 7/3/2006
Publication Date: 7/10/2006
Citation: Trabelsi, S., Nelson, S.O. 2006. Microwave sensing method for simultaneous and independent determination of bulk density and moisture content of shelled peanuts [CD-ROM]. IEEE AP-S Symposium and USNC/URSI and AMEREM Meetings. CD. pp. 3187-3190.
Interpretive Summary: Dielectric properties of materials are those electrical characteristics that determine how they interact with electromagnetic fields. For example, some materials are heated much more rapidly in a microwave oven than others. Those materials that heat rapidly have a higher dielectric loss factor than materials that do not absorb much energy from the microwave fields. The dielectric properties of materials such as grain and oilseeds are also closely related to the amount of water that they contain. Consequently, instruments can be designed to sense these dielectric properties and be calibrated to read moisture content. Such instruments, called moisture meters, are widely used in the grain and seed trade for rapid determinations of moisture content. Research has shown that microwave frequencies may offer advantages for the development of new reliable moisture meters. Moisture content is especially important in the sale and storage of peanuts so that spoilage and development of toxins can be avoided. This paper reports success in rapidly and nondestructively measuring both the moisture content and bulk density of shelled peanuts through microwave measurements. New moisture meters might be developed using these principles that would be helpful in preventing losses due to spoilage and provide useful tools to peanut farmers, handlers, and processors, thus providing high quality products for consumers.
Technical Abstract: Dielectric properties of shelled peanuts were measured with a free-space-transmission technique at 24 degrees C between 8.0 and 12.0 GHz over wide ranges of bulk density and moisture content. Resulting data for the dielectric constant and dielectric loss factor were each divided by bulk density and plotted in the complex plane. For any given frequency, data for all moisture contents and densities fell along a straight line with slope dependent only on frequency. From the equation of the straight line at any given frequency, bulk density was provided in terms of the dielectric properties. A density-independent moisture calibration equation was also obtained from which moisture content of the shelled peanuts can also be calculated in terms of the dielectric properties. Bulk densities were predicted from these microwave measurements with standard errors of 0.014 grams per cubic centimeter, and moisture contents were predicted with standard errors of 0.3 to 0.4 percent moisture content.