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United States Department of Agriculture

Agricultural Research Service

Title: Resonant Cavity Perturbation - Some New Applications of An Old Measuring Technique

Authors
item Kraszewski, Andrzej
item Nelson, Stuart

Submitted to: Journal of Microwave Power and Electromagnetic Energy
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: August 21, 1996
Publication Date: N/A

Interpretive Summary: New techniques are needed for rapidly sensing the quality characteristics of agricultural products. The electrical or dielectric properties of such products as grains and seed can be very rapidly sensed by electronic instruments to measure their moisture contents. Knowledge of moisture content is critical to safe storage and maintenance of good quality. When grain lots of different moisture contents are blended in the trade, spoilage in transit or in storage can occur when such lots are improperly mixed. Therefore, techniques for testing the moisture content of individual kernels or seeds in grain, soybean, and peanut samples could be helpful in preventing quality deterioration. Microwave resonant cavity measurements can provide the moisture contents of individual seeds and kernels. In addition, weight of these single objects can be determined at the same time by the microwave measurements. The measurements of moisture content and weight are fast, nondestructive, and could be developed for continuous monitoring. The results will be of interest to manufacturers supplying new measurement equipment for the agricultural trade. The technique has demonstrated potential for monitoring other properties of plastics and other dielectric objects, such as electrical permittivity and density. It would therefore be applicable in other industries as well as in agriculture.

Technical Abstract: Microwave resonators have been used as sensors for determining material properties of dielectric objects, including permittivity, density, moisture content, and mass from measurements of frequency shift and change in cavity transmission characteristics when a small dielectric object is inserted into a microwave resonant cavity. Fundamental principles of the shape- and size-independent measurements are discussed, and experimental results for moisture content and mass measurement of individual soybeans, peanuts and grain kernels, as well as for mass determinations on irregularly shaped objects of common plastic materials are presented. Measurements are fast, nondestructive, contactless, and have a potential for continuous operation.

Last Modified: 7/25/2014
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