Author
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Nelson, Stuart |
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Trabelsi, Samir |
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Submitted to: Book Chapter
Publication Type: Book / Chapter Publication Acceptance Date: 5/26/2010 Publication Date: 12/15/2014 Citation: Nelson, S.O., Trabelsi, S. 2014. Dielectric properties of agricultural products – fundamental principles, influencing factors, and measurement technirques. Book Chapter. p. 39-68. Interpretive Summary: Dielectric properties of materials are those electrical characteristics that determine their interaction with electric fields. In radio-frequency and microwave heating of foods, and other dielectric materials as well, it is the interaction of the materials with the electric field component of the electromagnetic waves that produces the desired heating effects. In this chapter, definitions of dielectric properties, or permittivity, of materials and a brief discussion of the fundamental principles governing their behavior with respect to influencing factors are presented. The basic physics of the influence of frequency of the electric fields and temperature of the materials on the values of the dielectric properties are also discussed. The influence of density, particularly the bulk density of granular and particulate materials, is discussed and equations are provided for correcting the relative complex permittivity (dielectric constant and loss factor) for variations in bulk density. A brief history of the dielectric properties of agricultural products is included and applications for such data are discussed. Tabulations and sources of information on the dielectric properties of agricultural products are cited. Many references for the dielectric properties of grain and seed and fresh fruits and vegetables and a few for poultry products are cited. Examples of dielectric properties data for these materials are presented graphically, most of which show the variation of the dielectric constant and loss factor with frequency and many show the dependence on temperature as well. The final major section is on measurement techniques used for the determination of the dielectric properties described and presented, spanning the frequency range from audio frequencies through radio frequencies well into the microwave frequency range. References are cited for detailed information on the many measurement techniques described. Technical Abstract: In this chapter, definitions of dielectric properties, or permittivity, of materials and a brief discussion of the fundamental principles governing their behavior with respect to influencing factors are presented. The basic physics of the influence of frequency of the electric fields and temperature of the materials on the values of the dielectric properties are also discussed. The influence of density, particularly the bulk density of granular and particulate materials, is discussed and equations are provided for correcting the relative complex permittivity (dielectric constant and loss factor) for variations in bulk density. A brief history of the dielectric properties of agricultural products is included and applications for such data are discussed. Tabulations and sources of information on the dielectric properties of agricultural products are cited. Many references for the dielectric properties of grain and seed and fresh fruits and vegetables and a few for poultry products are cited. Examples of dielectric properties data for these materials are presented graphically, most of which show the variation of the dielectric constant and loss factor with frequency and many show the dependence on temperature as well. The final major section is on measurement techniques used for the determination of the dielectric properties described and presented, spanning the frequency range from audio frequencies through radio frequencies well into the microwave frequency range. References are cited for detailed information on the many measurement techniques described. |
