THz-imaging: a new method for density mapping of wood

This paper presents a new technique for fast and non-intrusive density mapp ing of wood based on far-infrared spectroscopy. The transmission of a piece of beech 1.7 mm thick is investigated between 0.1 and 2.5 THz. In this spe ctral range we find wood to be fairly transparent, but density inhomogeneit ies and structural details such as annual rings become visible in the trans mission profile. The measured absorption correlates well with the wood dens ity independently obtained by the gravitometric-volumetric method. Thus it finally becomes possible to transform the THz images into 2-dimensional den sity maps.