Moisture-Dependent Structural Behavior and Permittivity Model for Granular Materials

Basic structural investigations on rape-seed as an example of a natural granular material with spherical shape are presented. Moisture dependent structure coefficients such as bulk and kernel density were measured in an especially developed apparatus. It was found, that density independence of a microwave moisture measurement could be obtained by applying a properly defined pre-pressure to a layer of material, thus obtaining moisture independent porosity and density. Furthermore, a permittivity model for rape-seed is presented, which relates dielectric constant, moisture content and structure coefficients. The various binding states ofwater as well as moisture dependent swelling of the seeds are included. The permittivity model was substantiated by dielectric measurements in X-band.