Microwave Dielectric Sensing of Moisture Content in Shelled Peanuts Independent of Bulk Density and with Temperature Compensation

Authors: Trabelsi, Samir; Nelson, Stuart

Submitted to: IEEE Sensor Applications Symposium
Publication Type: Proceedings
Publication Acceptance Date: 12/31/2007
Publication Date: 2/12/2008
Citation: Trabelsi, S., Nelson, S.O. 2008. Microwave Dielectric Sensing of Moisture Content in Shelled Peanuts Independent of Bulk Density and with Temperature Compensation. IEEE Sensor Applications Symposium.

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 determination of moisture content. Research has shown that microwave frequencies may offer advantages for the development of new moisture meters. Moisture content is especially important in the sale and storage of peanuts so that spoilage and development of toxins can be avoided. Microwave dielectric properties at a frequency of 10 GHz of shelled peanuts of different moisture contents were measured over a range of temperatures and bulk densities, or packing densities. Results were used to develop calibration equations for kernel moisture content, which predict moisture content independent of the bulk density of the shelled peanuts from their dielectric properties. This paper reports details of the microwave measurements of the dielectric properties and reveals that moisture content can be sensed by such measurements with accuracies of better than one percent moisture. With further development the microwave measurements offer good potential for saving time and labor in the moisture testing required when drying peanuts and testing them for safe storage and marketing. Microwave moisture meters 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: A dielectric method for rapid and nondestructive sensing of moisture content in shelled peanuts from free space measurement of attenuation, phase shift, and their corresponding dielectric properties at microwave frequencies is presented. Results of moisture prediction with three density-independent calibration functions are compared. For each function, the moisture calibration equation with temperature compensation is given.