Wood As An Orthotropic Dielectric Material

Richard T. Lin


When wood is treated as an orthotropic dielectric material, the relation between electrical displacement vector {D} and electrical field intensity vector {E} can be expressed as {D} = ϵ0 [k] {E}, where [k] is diclectric constant matrix. The transformation of the permittivity matrix then is [k] = [A] [k] [A]', where [A] and [A]' are the rotational matrix and its transpose.

The validity of the transformation equation was tested on western hemlock (Tsuga heterophylla [Raf.] Sarg.) specimens of various grain angle in the longitudinal-radial (LR), longitudinal-tangential (LT), and radial-tangential (RT) planes at 1 kHz and room temperature from green to oven-dry. The transformation equation applied to wood below 15% moisture content with a negligible error. The maximum dielectric constant of wood appears at the grain angle of 30 degrees in the LR plane and 15 degrees in the LT plane.

Discontinuity in the plot of the logarithm of dielectric properties versus moisture content was observed at 6 to 10% and 30 to 40% moisture content. Density of wood has little effect on dielectric properties of wood.


Tsuga heterophylla;grain angle;moisture content;AC resistivity;moisture meter

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