Non-destructive diagnosis of the integrity of green wood using ultrasonic computed tomography

Philippe Lasaygues (1) , Emilie Franceschini (1) , Eric Debieu (1) , Loïc Brancheriau (2)

1 LMA - Laboratoire de Mécanique et d'Acoustique [Marseille]
2 UPR Bois tropicaux - Production et valorisation des bois tropicaux

Ultrasonic computed tomography (UCT) was used to assess the integrity of green wood. Woods are heterogeneous air-coupled, orthorhombic materials. Because of the difference in acoustic impedance between the material and the surrounding medium (water or coupling gel), the ultrasonic wave propagation is greatly perturbed by physical processes such as the refraction, attenuation and scattering of the waves. UCT belongs to the inverse scattering class of problems and the aim of this study was therefore to present a strategy for simply, efficiently and accurately developing a reconstruction algorithm. UCT is based on several assumptions, such as the presence of a low contrast medium (the biological medium), a large frequency range (a broadband pulse), and dense and complete sets of projections. If these conditions are ideally fulfilled, we can reconstruct images of the impedance of the medium. This technique involves an algorithm based on first-order Born approximation methods. To date we have tested the qualitative aspects of this imaging technique and part of the quantitative aspects by performing numerical simulations and on our tomographic testing ground. The latter is composed of a base supporting a rotating and translating mechanical structure that can hold several transducers, and a numerical system and computing and recording the projections. When performing non-destructive assessments on wood, we would have liked to obtain quantitative images related to acoustic parameter of wood (impedance, speed of sound, attenuation). However, since the problem is non-linear, a low-frequency method involving signal and image processing was used.

Domaines: Acoustique [physics.class-ph]; Acoustique [physics.class-ph]

Philippe Lasaygues, Emilie Franceschini, Eric Debieu, Loïc Brancheriau. Non-destructive diagnosis of the integrity of green wood using ultrasonic computed tomography. International Congress on Ultrasonics, 2007, Vienne, Austria. CD-ROM(4 p.). ⟨hal-00440748⟩