Acoustic Tomography for Tension Wood Detection in Eucalypts

Abstract

The last two decades of the 20th century have been characterized by an extraordinary development of different methodologies for nondestructive evaluation of wood products, which has succeeded in the imaging of the internal structure of wood at both macroscopic and microscopic levels. The efforts devoted towards the development of nondestructive technologies for the evaluation of wood properties of trees, stems, logs and lumber are summarized in reference books (Pellerin and Ross 2002: Bucur 2003) and in the proceedings of the international symposia on non-destructive testing of wood. At the present time the predominant attention of the forest industry is oriented through imaging techniques development of the internal structure of wood or wood products, based on the propagation of different types of waves (electromagnetic or mechanical ). Given the hierarchical structure of wood, it is obvious that one should seek multi-scale characterization tools. The ultrasonic waves have a resolution between 10−3 and 10 −2 m, or more, depending on frequency (> 20 kHz) used for wood inspection. The ultrasonic waves propagated in wood are related to its elastic properties. The most common waves for ultrasonic imaging are the longitudinal waves. The resolution of ultrasonic imaging techniques is very much limited by the frequency, the wave length and by the size of the transducers. The main benefits of using acoustic techniques for wood quality assessment are that they are non-invasive and safe at a relatively low energy levels.