Microwave nondestructive testing for classification of Malaysian timber using free-space techniques

Microwave nondestructive testing methods are fast, contactless, accurate and continuous techniques for the evaluation of moisture content, slope-of-grain, density of knots and specific gravity of timber. Dielectric properties of timber are determined by these factors. We describe how the dielectric properties were deduced from reflection and transmission coefficient measurements of Malaysian timber specimens using a free-space measurement system in the frequency range 8-12.5 GHz. Dielectric properties were evaluated over different angles between the electric field and the direction of grain. Relationships between density, modulus of elasticity, strength, grain angle (angle between the direction of grain and electric field) and dielectric properties of Malaysian timber were established.