Permittivity measurement of wood material over a wide range of moisture content

Permittivity measurement of timber structures is important to ensure that its physical property lies within acceptable ranges. For example, permittivity dependence on moisture content can be useful to assess physical condition of wood. Permittivity is also a critical parameter that is needed for timber diagnosis using ground-penetrating radar (GPR) nondestructive technique. Different methods based on microwave measurements of these electromagnetic properties have been used in the past, but measurements over a wide range of moisture content are still needed, especially in the GPR frequency (1–2 GHz). This work presents measurements of relative permittivity values of spruce, pine and beech wood samples over a wide range of moisture content (up to 120%) using weak perturbation method at 1.26 GHz. Effects of moisture content, density and direction of fibers are observed. The main parameter influencing permittivity value is the quantity of water in wood material.