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United States Department of Agriculture

Agricultural Research Service

Research Project: SENSING METHODS & INSTRUMENTATION FOR RAPID DETERMINATION OF MOISTURE CONTENT... AND OTHER QUALITY ATTRIBUTES OF GRAINS, SEEDS, & NUTS

Location: Quality and Safety Assessment Research Unit

Title: Dielectric properties of grain and seed and their usefulness in sensing physical properties

Authors
item Nelson, Stuart -
item TRABELSI, SAMIR

Submitted to: ASABE Annual International Meeting
Publication Type: Proceedings
Publication Acceptance Date: June 3, 2013
Publication Date: N/A

Interpretive Summary: Permittivities or dielectric properties of materials are electrical characteristics that determine how materials 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 their 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 when it is put into storage. In this paper, dielectric properties are defined, and data on dielectric properties of grain and seed are presented showing the dependence of those properties on moisture content, frequency, temperature and bulk density of these granular materials. 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 grain and seed moisture sensing and can also sense the bulk density of these materials. Therefore, 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 both producers and consumers.

Technical Abstract: The importance of moisture measurement in grain and seed is discussed, and the usefulness of grain and seed dielectric properties in sensing moisture content of these materials is presented. Data are presented graphically for the 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 in higher frequency and microwave measurements for moisture content and bulk density sensing are described and numerous studies are cited providing sources of information on these newer techniques. Measurement at microwave frequencies offers means for sensing both moisture content and bulk density, thus providing density-independent moisture sensing and sensing of bulk density independent of moisture and temperature. Sensing of kernel moisture content in unshelled peanuts is also possible with microwave measurements

Last Modified: 9/10/2014
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