THE MEASUREMENT OF WOOD DENSITY BY MICROWAVE SENSOR

This paper presents the first results of wood density measurement using a microwave sensor. The information given by the sensor are amplitude variations and phase variations of the transmitted wave. This work concerns the calibration of the sensor. To eliminate the problem of wood anisotropy we used boards made from glued and pressed sawdust. There are 5 kinds of sawdust and from each five different board densities were prepared. The first measurements concerned the geometry and the reliability of the sensor. The results show that the sensor does not present defect geometry and that its readings are reliable. Then we looked for a relationship between board density and the variations of the microwave parameters. An accurate linear relationship was found, but it appears to be necessary to consider each sawdust type separately. Based on these results we prepared other samples with different glue contents to control the influence of glue on microwave parameters. The results show that in our ranges of densities (0.55-0.75 g/cm3) and glue contents (6-12%) the influence of glue is negligible. Further on, it appears that measuring the amplitude variation may be a means for controlling the granulometry of particle boards.