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Radio-Frequency and Microwave Dielectric Properties of Fresh Fruits and Vegetables

Published by the American Society of Agricultural and Biological Engineers, St. Joseph, Michigan

Citation:  Paper number  036196,  2003 ASAE Annual Meeting . (doi: 10.13031/2013.13923) @2003
Authors:   Stuart O. Nelson
Keywords:   Dielectric constant, Dielectric loss factor, Fresh fruits, Fresh vegetables, Permittivity

The relative complex permittivity, consisting of the dielectric constant and loss factor, were measured for samples cut from nine fresh fruits and vegetables over the frequency range from 10 MHz to 1.8 GHz at temperatures ranging from 5 to 95 C. Permittivity data are presented graphically for apple, avocado, banana, cantaloupe, carrot, cucumber, grape, orange, and potato, showing dielectric constants ranging from values of several hundred at 10 MHz to less than 100 at 1.8 GHz and loss factors of several hundred to a few thousand at 10 MHz to much less than 100 at 1.8 GHz. The dielectric loss factor generally increased with increasing temperature. The dielectric constant increased with temperature at lower frequencies, but it decreased with temperature at the higher frequencies. There was a point in the frequency range between 10 MHz and 100 MHz where temperature dependence of the dielectric constant was minimal. At frequencies below this point, ionic conduction dominated the dielectric behavior, but above that point dipolar relaxation appeared to control the behavior. Moisture content, density, and total soluble solids content of the fruit and vegetable samples were measured, but poor correlation was observed between these characteristics and the dielectric properties across the selection of fruits and vegetables. The data provide new information useful in understanding dielectric heating behavior and evaluating dielectric properties of such agricultural products for quality sensing applications.

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