Source Year: 1997

Dielectric constants of leaves of rubber (Hevea brasiliensis) and oil palm (Elaeis guineensis) were measured at microwave frequency. Using a microcomputer-based automated system consisting of a Wiltron 360B vector network analyser, measurements were conducted based on the waveguide thin sheet technique. Leaf saples were inserted within waveguide sections, and the dielectric constants were calculated from the complex reflection coefficients. The measurements covered a frequency range of 4-18 GHz. In general, the dielectric constant of a leaf sample was a function of water content and frequency. Theoretical calculations from 3 dielectric mixing models were compared with the measurements. From these comparisons, the Debye-Cole dual-dispersion model showed the most promise for prediction of dielectric constants, if proper physical parameters of the model, such as bound and free-water volume fractions, were used.