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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: Techniques for Measuring the Dielectric Properties of Agricultural Products

Authors
item Nelson, Stuart -
item TRABELSI, SAMIR

Submitted to: ASABE Annual International Meeting
Publication Type: Proceedings
Publication Acceptance Date: June 18, 2012
Publication Date: July 29, 2012
Citation: Nelson, S.O., Trabelsi, S. 2012. Techniques for Measuring the Dielectric Properties of Agricultural Products. ASABE Annual International Meeting. Paper No. 121338238.

Interpretive Summary: Dielectric properties of materials are electrical properties that determine how materials interact with electric fields such as those of high-frequency and microwave electromagnetic energy. Therefore, the dielectric properties of materials determine how rapidly they will heat in microwave ovens and lower radio-frequency dielectric heating equipment. Dielectric properties are also important in low power applications, such as the rapid measurement of moisture content in grain and other commodities. Therefore it is often important to measure the dielectric properties of materials at the frequencies of interest in any application. In this article, dielectrics as a class of substances, along with the dielectric properties of materials are defined generally. Principles for measuring the dielectric properties and techniques that have been successfully used in measuring the dielectric properties of different agricultural products at frequencies ranging from audio frequencies through radio frequencies and well into the microwave range are briefly described, and references are cited for more detailed information on those techniques. Citations are provided where the dielectric properties of grain and seed, fruits and vegetables, insects, food materials, coal, minerals, limestone and other materials are presented. The information presented is of interest to engineers and scientists in developing instruments that can provide important tools for improving agricultural production, product processing, product quality preservation, and marketing for the benefit of growers, processors and consumers.

Technical Abstract: Dielectrics and dielectric properties of materials are defined generally, and methods for measuring dielectric properties of agricultural products are described for several frequency ranges from audio frequencies through microwave frequencies. These include measurement with impedance and admittance bridges, resonant circuits, and transmission-line and free-space methods in the frequency domain and time-domain and broadband techniques. Many references are cited that describe the methods in detail and provide data on the dielectric properties or permittivities of agricultural products.

Last Modified: 8/19/2014
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