Dielectric Behavior of Douglas-Fir At Various Combinations of Temperature, Frequency, and Moisture Content

Dielectric constant and loss tangent are given here for the longitudinal direction in Douglas-fir, at temperatures from -20? to 90?C, at moisture contents from ovendry to saturated, and at frequencies from 20Hz to 50 MHz. A theory based on a physically plausible model and assumptions demonstrates that wood and wood-based materials consist of polarizable elements with a continuous and nearly uniform distribution of time constants within each of three major segments. The theory and model are shown to account for the observed effect of frequency on the dielectric properties of Douglas-fir. The influences of frequency and moisture content were shown to be greater than the influence of wood species. The data presented will be useful for electrical design where wood is subjected to alternating electric fields.

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