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United States Department of Agriculture

Agricultural Research Service

Title: Some Agricultural Applications for Dielectric Spectroscopy

Author
item Nelson, Stuart

Submitted to: International Conference on Broadband Dielectric Spectroscopy and Its Applications
Publication Type: Abstract Only
Publication Acceptance Date: September 2, 2002
Publication Date: September 1, 2002
Citation: NELSON, S.O. SOME AGRICULTURAL APPLICATIONS FOR DIELECTRIC SPECTROSCOPY. SECOND INTERNATIONAL CONFERENCE ON BROADBAND DIELECTRIC SPECTROSCOPY AND ITS APPLICATIONS, LEIPZIP, GERMANY. 2002. p. T60.

Technical Abstract: Dielectric properties of agricultural products are of interest for several reasons. These include the sensing of moisture content through its correlation with the dielectric properties, or permittivities, of cereal grain and oilseed crops, the influence of permittivity on the dielectric heating of products at microwave or lower radio frequencies, and the potential use of permittivities for sensing quality factors other than moisture content. Information on dielectric properties across broad ranges of frequency, which implies dielectric spectroscopy, has been of interest in assessing the best frequency range to use for selective heating of insects that infest grain and other products. Early measurements of the permittivity of adult rice weevils and hard red winter wheat were obtained at frequencies from 250 Hz to 12 GHz with an assortment of eight different frequency-domain measurement systems, each covering a narrow range of frequencies. The frequency range from about 10 to 100 MHz was identified as the optimum range for selectively heating the insects, where the loss factor of the insects was about five times greater than that of the wheat. Open-ended coaxial-line probe measurements were more recently obtained on four species of stored-grain insects from 200 MHz to 20 GHz. Open-ended probe permittivity measurements were also used to study the frequency dependence of the dielectric constant and loss factor of many fresh fruits and vegetables. The possibility of sensing maturity of fresh peaches was also explored,with some potential indicated for a permittivity-based maturity index, but much further work is required for proper assessment of the technique. Similar measurements, with a temperature controlled sample holder, were used to study the frequency and temperature dependence of the permittivities of some food materials from 10 MHz to 1.8 GHz. In the 0.2- to 20-GHz range, effects of ionic conduction and dielectric relaxation attributable to liquid water were evident in resulting data for apple juice. Time-domain reflectometry was also explored for permittivity measurements, and data were reported for rice weevils, wheat, and alfalfa seed from 30 MHz to 1 GHz. With further development of suitable sample holders for agricultural materials, permittivity data over wider ranges of frequency might be more efficiently obtained through time-domain spectroscopy for applications in agriculture

Last Modified: 12/21/2014
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