Wood NDT-2000 Session VI.: Microwave and Miscellaneous
Microwave Polarimetry Dased Wood Scanning
Anders Kaestner Halmstad University, Box 823, S-301 18 Halmstad, Sweden email:anders.kaestner@ide.hh.se
ABSTRACT
We describe a method to detect knots and faults in wood logs based on microwave measurements and the depolarising properties of wood. The depolarisation is an effect of the anisotropy in the dielectric properties of wood, which is caused by the fibre structure. The measurements are made in the frequency domain where a discrete reflec-tion spectrum is sampled. By transforming the frequency spectrum into the time domain the spatial distribution of the reflections appear. The wave is transmitted in a pure linear polarisation, tilted to 45° For each discrete frequency all available information is measured for the reflected wave and therefore it is possible to calculate the complex polarisation ratio and the state of polarisation which are the quantities containing the most visible information. The measurements are one dimensional and by combining measurements from different directions we create tomographic slice images of the inner structure of a log. Our measurements has showed the possibility to follow the extension of knots in a log using only a iso-surface visualisation. The used equipment is working at low intensity and is therefore virtually harm-less to human beings, furthermore it is portable and can be operated by one single person.
Publication Source: Proceedings of the 12th International Symposium on Nondestructive Testing of Wood University of Western Hungary, Sopron, 13-15 September 2000, ISBN 963 7180 88 5 Publisher: University of Western Hungary, H 9400 Sopron, P.O.Box 132, FAX: +36 99 311 103
