Detection of decay in wood using microwave characterization

The transparency of wood to microwave radiation is subject to changes in the wood´s properties caused by the fungal attack. A prototype microwave system that measures microwave attenuation and phase delay between two antennae was developed to detect fungal decay in wood at equilibrium moisture content. In this study Pinus radiata (D. Don) (softwood) and Eucalyptus regnans (F. Mueller) (hardwood) of the same dimensions were exposed to soil containing decay fungi for 12, 16, 20 and 24 weeks in an Accelerated Field Simulator Samples were washed and dried in an oven before testing with the prototype system. In order to get a preliminary set of microwave permittivity, a dielectric probe technique is used. A patch antenna set-up was used for detailed study. Orienting the antennae such that the microwave field was perpendicular to the wood grain could not distinguish between sound and decayed wood; however orienting the antennae so that the microwave fields were parallel to the wood grain and having the antennae pressed against the wood sample easily distinguished between sound wood and decayed wood. The phase delay data could not distinguish between sound or decayed wood.