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Title: SOME APPLICATIONS FOR DIELECTRIC SPECTROSCOPY IN AGRICULTURE

Author
item Nelson, Stuart

Submitted to: National Radio Science Meeting
Publication Type: Abstract Only
Publication Acceptance Date: 5/25/2005
Publication Date: 7/3/2005
Citation: Nelson, S.O. 2005. Some applications for dielectric spectroscopy in agriculture [abstract]. URSI Digest, USNC/CNC/URSI North American National Radio Science Meeting, July 3-9, Washington, DC. Session 105-4 CDROM.

Interpretive Summary:

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 has been of interest in assessing the best frequency range to use for selective dielectric heating of insects that infest grain and other products. Early measurements of the permittivity of adult rice weevils and hard red winter wheat at frequencies from 250 Hz to 12 GHz identified the frequency range from 10 to 100 MHz as the optimum range for selectively heating the insects. In this range, the dielectric 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. Similar 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 efficiently obtained through time-domain spectroscopy for applications in agriculture.