FREQUENCY AND TEMPERATUREDEPENDENT PERMITTIVITIES OF FRESH FRUITS AND VEGETABLES FROM 0.01 TO 1.8 GHZ

Abstract

The relative complex permittivity, consisting of the dielectric constant and loss factor, were measured for samplescut from nine fresh fruits and vegetables over the frequency range from 10 MHz to 1.8 GHz at temperatures ranging from 5.Cto 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 GHzand loss factors of several hundred to a few thousand at 10 MHz to much less than 100 at 1.8 GHz. The dielectric loss factorgenerally 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 and100 MHz where temperature dependence of the dielectric constant was minimal. At frequencies below this point, ionicconduction 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 poorcorrelation was observed between these characteristics and the dielectric properties across the selection of fruits andvegetables. The data provide new information useful in understanding dielectric heating behavior and evaluating dielectricproperties of such agricultural products for quality sensing applications.