A 10 GHz microwave bridge measurement system has been developed to automatically measure the electromagnetic field parameters transmitted through a dielectric material. These parameters are used to calculate the complex dielectric constant with the free-space transmission technique. The system is used to measure the field parameters transmitted through dimension lumber and a correlation is made with two strength determining factors of lumber: specific gravity and moisture content. Hemlock and Douglas Fir wood samples were tested and a grading technique was implemented. The system is capable of estimating the specific gravity to ±0.05 accuracy and the moisture content to ±3.0% accuracy. / Applied Science, Faculty of / Electrical and Computer Engineering, Department of / Graduate

The focus of this research is to develop a prototype expert system for softwood lumber grading. The grading rules used in the knowledge base of the system are based on Western Lumber Grading Rules 88 published by the Western Wood Products Association. The system includes 27 grades in Dimension, Select/Finish, and Boards categories. The system is designed to be interactive and menu-driven. The user input to the system consists of lumber size, grade category, and type, location and size of defects for each face. The system then infers the grade corresponding to each face, and an overall grade for the lumber. The system provides limited explanation capabilities. Evaluation of the system was performed using 85 samples of pre-graded Siberian larch 2x4x12s in Structural Light Framing category. The initial evaluation was performed using the two wide faces of boards. Results indicated a 60 percent match between the grade assigned by the human expert and the system. The largest cause of deviation was exclusion of defects on the two narrow faces. The knowledge base was expanded to include the two narrow faces; the match rate improved to 76.5 percent. Evaluations for other grading categories need to be conducted in the future to assess the adequacy of the knowledge base. The prototype development concentrates on selected defect characteristics for each grade. These characteristics are clearly defined and described in the rule book, and are usually the most frequently encountered defects on softwood lumber. The knowledge base needs to be refined and expanded if additional factors such as knot positions relative to each other, warp, manufacturing imperfections and clustering of defects are to be considered. / Graduation date: 1993