Dielectric Properties of Wood and Hardboard: Variation with Temperature, Frequency, Moisture Content, and Grain Orientation.

The dielectric constant and loss tangent of white oak, Douglas-fir, and four commercial hardboards were measured at frequencies from 20 HertzHz to 50 MegahertzMHz, moisture conditions from ovendry to complete saturation, temperatures from -20 to 90C., and, for the natural wood, with the electric field alined with three principal structural orientations. The hardboard was measured with the electric field perpendicular to the faces of the board. The behavior of all materials studied was qualitatively similar. The dielectric constant increased with increasing moisture content or temperature, and decreased with increasing frequency.