|Hansen, James D|
Submitted to: Biosystems Engineering
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/25/2003
Publication Date: 4/29/2003
Citation: Wang, S., Tang, J., Johnson, J.A., Mitcham, E., Hansen, J.D., Hallman, G.J., Drake, S.R., Wang, Y. 2003. Dielectric properties of fruits and insect pests as related to radio frequency and microwave treatments. Biosystems Engineering. 85:201-212. Interpretive Summary: There has been an increasing interest in using radio frequency and microwave energies as new heat treatments for control of postharvest insects in agricultural commodities. Electromagnetic energy interacts directly with commodities to raise interior temperatures and significantly reduce treatment times from those needed with conventional hot water dips and hot forced air methods. Heat treatments for insect control using radio frequency and microwave systems leave no chemical residues on products and have minimal impacts on the environment. Consequently, radio frequency and microwave treatments are being considered as alternatives to chemical fumigants for the control codling moth in cherries, and codling moth and navel orangeworm in walnuts. Knowledge of dielectric properties of insects and commodities is necessary when developing radio frequency and microwave treatment protocols. Dielectric properties of six commodities and four associated insect pests were measured from 1 - 1800 MHz and at temperatures between 20 and 60°C. Both dielectric constant and loss factor of nuts were very low compared to those of fruits and insects. The large difference in the loss factor between insects and nuts at 27 MHz suggests that insects may heat faster than nuts when treated in a radio frequency system, resulting in rapid kill of infesting insects without causing damage to the product. Dielectric properties of fruits may be used in designing saline water solutions that allow uniform heating of fruit core and surface.
Technical Abstract: 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 60 degrees C. 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 27MHz. The large difference in the loss factor between insects and nuts at 27MHz suggests possible differential heating of insects in nuts when treated at the same time in a RF system.