Dielectric properties of defects on wood surfaces Public Deposited

http://ir.library.oregonstate.edu/concern/graduate_thesis_or_dissertations/1j92g9360

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  • Raw material costs and limited material availability and quality have created significant interest in and opportunities for the application of nondestructive evaluation techniques to improve wood processing technologies. The incentives come from the desire to 1) manufacture the highest valued product, 2) conserve the amount of raw material used, 3) use lower priced and often, lower quality raw materials, and 4) meet future demands for wood products in an economy with stark contrasts of a declining wood supply and increasing pressure from environmental concerns. Developing appropriate non-destructive evaluation techniques requires research and development of new concepts and extending the usability of known principles. Dielectrics is one such technique that offers a number of potential applications in areas such as moisture detection, drying and re-drying, grading and sorting, defect detection, curing and gluing of engineered products, repairing and patching of laminated panel products, monitoring of adhesive curing, and manufacturing of aligned fiber products. The objective of this research was to fill the void in knowledge that existed about the dielectric properties of typical features found on Douglas-fir (Pseudotsuga menziesii) wood. Features investigated included clearwood, various sizes of loose and tight knots, knot holes, pitch pockets, pitch streaks, and blue stain. The dielectric constant and loss tangent were analyzed on a global (whole-feature) basis under a range of excitation frequencies and moisture content conditions typically found in wood processing. This research required the development of specialized instrumentation, because measuring the dielectric properties of wood over a broad full range of moisture and excitation frequency conditions is particularly challenging. Results suggested that there are optimal combinations of moisture and excitation frequencies suitable for applications where it is necessary to distinguish between certain wood features. Simple classifications of features measured at such optimal working conditions are presented in addition to global data on the expected dielectric properties of each feature. These results form a fundamental basis for the development of future stand-alone, dielectric-based applications or applications using dielectric-based in conjunction with and other sensing methods.
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