The effect of thermal treatment temperature on the dielectric properties of beech (Fagus sylvatica L.) and spruce (Picea abies L.) was investigated. Wood disks with a diameter of 45 mm and a thickness of 5 mm were thermally treated at seven different temperatures (50 to 200 °C) before measurements were performed. Dielectric properties of the wood disks were measured at nine various frequencies (2 to 10 MHz) at room temperature. The impedance analyzer HP 4191A RF and the micrometer screw method with circular aluminum electrodes were used. The results indicate that the dielectric constant and the loss tangent of wood decrease as the temperature of the thermal treatment increases, provided the temperature is higher than 100 °C. The dielectric constant also decreases with increasing weight loss of the specimen
