An innovative tomographic technique integrated with acoustic-laser approach for detecting defects in tree trunk

In this study, we develop a tomographic technique based on the use of both mechanical wave (i.e. stress wave and acoustic wave) and electromagnetic wave (i.e. laser beam) for evaluating the defects in tree trunk. In the experimental work, the tomographic technique was used to inspect tree trunk with an air hole fabricated at the centric position and air gaps made at 5–50 mm near from surface. The result indicates that the internal air hole and the air gap located within 5–20 mm below the tree surface can be effectively detected and quantified. Compared to the results from conventional sonic tomography, our tomographic technique can achieve a more accurate and reliable detection of internal defect in tree system, especially if the internal defects are close to the free surface (i.e. critical defects associated with bending failure).