Dielectric properties of biomass by-products generated from wood and agricultural industries in Finland.

Knowledge of the dielectric properties (complex permittivities) of biomasses is critical for understanding their behaviors in a microwave field and for designing large-scale microwave systems. The present research was focused on determining the dielectric properties of different types of biomasses (sawdust, bark, fiber reject, grass, and straw) at temperatures from 25 to 700 °C and frequencies in the range of 397 to 2985 MHz, using cavity perturbation technique. The dielectric properties decreased during the drying (25 to 200 °C) and the pyrolysis stages (200 to 400 °C), but sharply increased during the biochar formation stage (400 to 700 °C).