ARS | Publication request: Microwave Permittivity Determination in Agricultural Products

Submitted to: Journal Of Microwave Power And Electromagnetic Energy
Publication Acceptance Date: April 22, 2004
Publication Date: August 10, 2004
Citation: Kraszewski, A.W., Nelson, S.O. 2004. Microwave Permittivity Determination In Agricultural Products. Journal Of Microwave Power And Electromagnetic Energy. 39 (1): 41-52.

Interpretive Summary: There is a need in modern agriculture for new methods of sensing physical and other properties of products to determine when they are ready for harvest, to measure rapidly certain quality aspects of the products, and to measure their condition at various points in the processing and storage operations. The microwave dielectric properties (electrical characteristics) of products such as grain and seed can be rapidly sensed with proper instruments, and since these properties are well correlated with moisture content, microwave measurements provide a rapid means of determining moisture content. Other quality factors of agricultural products can likely be sensed through the dielectric properties of the products. For studying these potential new methods of quality sensing, it is important to measure the dielectric properties, or permittivity, of products and correlate these properties with quality factors of importance for particular products. This paper reviews the various techniques for measuring the microwave permittivities of agricultural products, such as grain, seeds, plants, fruits, vegetables, meats and other foods. Dielectric properties data obtained by such measurements are shown for several different products, and their variation with moisture content, temperature, frequency of the applied microwaves, and density of the products are illustrated. The review provides useful information to those scientists interested in research for the development of new sensors for better quality control and utilization of agricultural products that will provide new tools for managing grading and processing of such products for competetive advantages in the global market place.

Technical Abstract: Applications of microwave measurement techniques, including frequency-domain and time-domain methods, for determining the permittivity of agricultural products (seeds, plants, grains, fruits, meat, etc.) are reviewed. Graphical data illustrating the dependence of the dielectric constants and loss factors of such products on moisture content, frequency of the applied fields, temperature, and bulk density of granular materials are provided for selected materials. Finally, recommendations are offered for further study and applications of permittivity measurements.