MICROWAVE DIELECTRIC-PROPERTIES OF RUBBER AND OIL PALM LEAF SAMPLES -MEASUREMENT AND MODELING

This paper contains the results of measured dielectric constants of le aves of two tropical crops, rubber (Heavea brasiliensis) and oil palm (Elaeis guineensis) at microwave frequency region. Using a microcomput er-based automated system consisting of a Wiltron 360B vector network analyser, measurements are conducted based on the waveguide thin sheet technique. Leaf samples are inserted within waveguide sections, and t he dielectric constants are calculated from the complex reflection coe fficients. The measurements cover a frequency range of 4-18 GHz. In ge neral, the dielectric constant of a leaf sample is a function of water content and frequency. Theoretical calculations from three dielectric mixing models, i.e., the Debye-Cole Dual-Dispersion dielectric model by Ulaby and Rayes, Matzler's Model and Carlson's Model are compared w ith the measurements. From the comparisons, the dual-dispersion model is found to show more promise in prediction of the dielectric constant s, if proper physical parameters of the model, such as bound and free- water volume fractions, are used.