Dielectric properties of fruits and insect pests as related to radio frequency and microwave treatments

Information on dielectric properties of commodities and insect pests is needed in developing thermal treatments for postharvest insect control based on radio frequency (RF) and microwave energy. Dielectric properties of six commodities along with four associated insect pests were measured between 1 and 1800 MHz using an open-ended coaxial-line probe technique and at temperatures between 20 and 60degreesC. The dielectric loss factor of fresh fruits and insects decreased with increasing frequency at constant temperatures. The loss factor of fresh fruits and insects increased almost linearly with increasing temperature at 27 MHz radio frequency, but remained nearly constant at 915 MHz microwave frequency. Both dielectric constant and loss factor of nuts were very low compared to those of fresh fruits and insects. The temperature effect on dielectric properties of nuts was not significant at 27 MHz. The large difference in the loss factor between insects and nuts at 27 MHz suggests possible differential heating of insects in nuts when treated at the same time in a RF system. (C) 2003 Silsoe Research Institute. All rights reserved Published by Elsevier Science Ltd.