Author
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Nelson, Stuart |
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Submitted to: Journal of Microwave Power and Electromagnetic Energy
Publication Type: Peer Reviewed Journal Publication Acceptance Date: 4/1/2004 Publication Date: 1/20/2005 Citation: Nelson, S.O. 2004. Agricultural applications of dielectric spectroscopy. Journal of Microwave Power and Electromagnetic Energy. 39(2):75-85. Interpretive Summary: Dielectric properties of materials are those electrical characteristics of the materials that determine their interaction with electric fields. If the electric fields are of sufficiently high frequency and of sufficient intensity, many materials can be rapidly heated. The use of microwave ovens for heating foods is a familiar example of such applications. These same dielectric properties of materials can be sensed by appropriate instruments using very low level electric fields for purposes of measurement. The correlation of the dielectric properties with moisture content of the materials can be used with appropriately designed instruments for rapidly determining the material moisture content. This is the principle used in grain moisture meters, which can provide instantaneous readings for moisture content. Such instruments generally use only one or two frequencies at which the sensing is done. By studying the variation of the dielectric properties of agricultural products over wide ranges of frequency, correlations between dielectric properties and quality factors other than moisture content may be found. The study of the dielectric properties variation over broad ranges of frequency is termed dielectric spectroscopy. Several applications for dielectric spectroscopy in agriculture are presented in this paper, and data are presented that show the usefulness of the technique. These studies provide background data for potential new applications that include sensing the quality of fruits and vegetables. Technical Abstract: A brief review is presented of dielectric spectroscopy applications in agriculture. Included are wide frequency range (250 Hz to 12 GHz) permittivity, or dielectric properties, measurements on adult rice weevils and hard red winter wheat, for the purpose of assessing selective dielectric heating of the insects, and broadband (200 MHz to 20 GHz) permittivity measurements on tissues of fresh fruits and vegetables. Similar measurements are shown for tree-ripened peaches, which were obtained to assess possibilities for a permittivity-based maturity index. Broadband (10 MHz to 1.8 GHz) permittivity measurements are shown for several fruits and vegetables as a function of temperature from 5 to 95 degrees C. Measurements over the same frequency range and similar temperature ranges are presented for two other food products, whey protein gel and apple juice. A few comments are offered on likely future dielectric spectroscopy applications in agriculture. |
