Determination of density and moisture content of wood using Terahertz time domain spectroscopy.

Terahertz time-domain spectroscopy was used to simultaneously predict the density and moisture content of four wood species (Aspen, Birch, Hemlock and Fir). Using a fixed value for the dielectric function of water, it was found that moisture content was systematically underestimated at low moisture contents, which results from changes in the dielectric function of water as it goes from free to bound in nature. The variation of the dielectric function of water with moisture content was studied further, and the results show that the dielectric function of water does indeed change with moisture content. The results are a large step forward in our understanding of wood-water interactions at Terahertz frequencies, and therefore useful for applications in wood science. --Leaf i.