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Abstract
Dielectric spectroscopy data from
measurements on tissue samples of nine fresh fruits and vegetables were used
to study their dielectric behavior over the
frequency range from 10 MHz to 1.8 GHz at 5 to 65 °C. Dielectric constant
and loss-factor 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 on the order of one thousand at 10 MHz to less
than 20 at 1.8 GHz. The dielectric loss factor increased consistently with
increasing temperature at frequencies below 1 GHz. The dielectric constant
increased with temperature at lower frequencies, but it decreased with
temperature at the higher frequencies. This reversal of the sign of the
temperature coefficient occurred at some point in the frequency range between
20 and 120 MHz where the temperature dependence of the dielectric constant
was zero. At frequencies below this point, ionic conduction dominates the dielectric
behavior, but above that point dipolar relaxation
appears to control the behavior. Multiple linear
regression provided equations for calculation of the loss factor in the
frequency range from 10 to 300 MHz at temperatures from 5 to 65 ° C. 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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