Dielectric Study of Water Binding in Grain

Abstract

Dielectric properties of wheat samples, in which moisture equilibrium was upset by adding water, were tracked versus time in the frequency range between 5 GHz and 15 GHz at room temperature (23 oC). Results presented at 10 GHz show an initial drop in the dielectric constant and loss factor, which reflects the initial stages of water binding, followed by a plateau indicating the final binding level of the water molecules in the wheat kernels. With application of a density-independent calibration algorithm, the apparent moisture content was predicted in each sample from measurement of the dielectric properties. As expected, for each wheat sample, the predicted initial moisture content was higher than the reference oven moisture content and decreased as time increased. This study shows that dielectric-based moisture sensors require correction when used for sensing moisture content in nonequilbrated materials.