Dielectric Properties of Typical Australian Wood-Based Biomass Materials at Microwave Frequency

Recent progress in microwave characterization of wood based materials has created a need for better understanding of dielectric properties of these materials, which influence the absorption of electromagnetic energy. In the present study the dielectric measurements were carried out for typical Australian wood species such as Slash pine (Pinus elliottii, a softwood species), and Spotted gum (Eucalyptus maculata, a hardwood species), based on Von Flippers transmission line method. The influence of extractive removal was also studied and compared with the virgin wood samples. Measurements were performed at 9.47 GHz for both virgin and extractive-free wood samples. Experiments were carried out at atmospheric pressure under a range of ambient temperatures between 20 and 25 degrees C. The dielectric properties of wood species were determined as a function of controlling factors such as density, moisture content, and fiber directions. Moisture content varied from 0% to 13% for virgin wood samples at atmospheric equilibrium conditions. Results indicated that the dielectric properties of both wood species were affected by density, moisture content, and fiber directions. In general, for virgin wood samples, the dielectric property was found to increase with density and moisture content. The values of the dielectric property in parallel direction to the stem were generally higher than those in the perpendicular direction for virgin sample of both wood species. However, such a trend was not observed for extractive-free wood samples.