Microwave nondestructive evaluation of timber using a metal - backed reflection technique/ Razimah Abdul Rahim

Dielectric properties of timber are determined by its moisture content, slope-ofgain and density. So, they can be used for nondestructive evaluation of timber. Dielectric properties will be deduced from complex reflection coefficient measurements of metal-backed Malaysian timber specimens. A free-space microwave measurement system is used for reflection coefficient measurements in the frequency range of 7.5-14.5 GHz. The key components of the measurement system are a pair of spot-focusing horn lens antennas, the microwave network analyser and computer. The inaccuracies in free-space measurements due to diffraction and multiple reflections are minimized by the use of spot-focusing antennas and free-space LRL ( Line, reflect and line ) calibration technique. Experimental results will be reported for dry and wet specimens of different types of Malaysian timber. Also, dielectric constant and loss tangent values will be measured when the electric field is parallel and perpendicular to the grain direction.