Submitted to: Microwave Power Symposium Proceedings
Publication Type: Proceedings
Publication Acceptance Date: 6/17/2010
Publication Date: 7/14/2010
Citation: Nelson, S.O., Trabelsi, S. Microwave Sensing of Density and Moisture in Granular Materials. Proceedings of the 44th Annual Microwave Power Symposium, Denver, CO, July 14-16, 2010, pp. 228-232. Interpretive Summary: Dielectric properties of materials are electrical characteristics that determine how they interact with electric fields. For example, these properties determine how rapidly the material will heat in a microwave oven. The dielectric properties of grain and seed are highly correlated with moisture content, so electronic instruments have been designed to sense these properties for rapid measurement of grain and seed moisture content. Such grain and seed moisture meters have long been used for determination of grain moisture content when it is traded and going into storage. Improvements in grain moisture meters and grain moisture monitoring equipment are desirable, because moisture content is such an important factor in determining safe storability of grain and seed. The historical development of grain and seed moisture meters is outlined in this paper, and a review of the pertinent literature reporting grain and seed dielectric properties is included. Fundamental definitions of dielectric properties are given, and a discussion of the factors, such as frequency, moisture content, grain bulk density, and temperature, is included. Currently used moisture meters use frequencies between 1 and 20 MHz for sensing the dielectric properties and providing moisture contents of grain and seed. Microwave frequencies well above those in current use have shown promise for improving the reliability of such instruments. Therefore, those studies are reviewed and the fundamental principles in simultaneously sensing moisture content and grain and seed bulk density as well are presented. The microwave measurements can be used for reliable measurements of grain and seed moisture content in static and flowing grain, so they offer promise for improved monitoring of moisture in granular materials. These advances will aid the commercial development of new techniques for practical use and provide new tools for managing moisture content and quality of grain and oilseed and their products for the benefit of both producers and consumers.
Technical Abstract: The importance of moisture measurement in grain and seed is discussed, and a brief history of the development of moisture sensing instruments, based on sensing of dielectric properties of these materials, is presented. Data are presented graphically on the permittivities or dielectric properties of grain and seed showing their variation with frequency, moisture content, temperature, and bulk density, and references are cited for further information. More recent developments on microwave measurements for moisture content and bulk density sensing are briefly described, and numerous studies are cited providing sources of information on these promising techniques.