Temperature dependence of the dielectric properties of rubber wood

The effect of temperature on the dielectric properties of rubber wood were investigated in three anisotropic directions-longitudinal, radial, and tang ential, and at different measurement frequencies. Low frequency measurement s were conducted with a dielectric spectrometer, and high frequencies used microwave applied with open-ended coaxial probe sensors. Dielectric constan ts and dielectric loss factors were measured at temperatures from 25 to 100 degreesC. A large dielectric dispersion occurred at frequencies less than 10 Hz and at temperatures more than 60 degreesC. The minimum peak value of the dielectric loss factors shifted towards higher frequencies at higher te mperatures in all three grain directions. The tangential direction showed t he highest activation energy. The dielectric constant decreased as frequenc y increased from 1 to 10 GHz, and thereafter remained unchanged with additi onal frequency increases. The dielectric constant exhibited higher values a t higher temperatures. The dielectric loss factor showed a peak value at ar ound 10 GHz at 25 degreesC.