The effect of frequency and temperature on dielectric properties of wood with high moisture content

Abstract Dielectric sensors are a popular choice for determining wood moisture content. However, the output of these devices, especially when measuring high moisture content, may be significantly affected by the moisture content itself, by sensor frequency (f) and by environmental temperature (T). This study investigated the effect mechanism of f and T on dielectric properties of wood with different moisture contents. Dielectric constant (ε) and dielectric loss factor (tan δ) for Populus nigra, Tilia tuan, Abies fabri and Fraxinus mandshurica wood samples of various moisture contents were measured from 1 to 107 Hz and from – 40 to 25 °C. The results show that wood ε increases with increasing moisture content and temperature, and decreases with increasing f. The dielectric constant depends significantly on f when T exceeds 6 °C, the rate of ε decreases with increasing f. At room temperature, tan δ of wood with moisture content >50% were not related, and peaked between 103 and 104 Hz. The change of tan δ with T is complex. The results provide a basis for in-depth research on the dielectric properties of wood with high moisture content and a theoretical basis for the measurement and calibration of the moisture content of standing trees.