Ian D. Hartley

Origin of Birefringence in Wood at Terahertz Frequencies

In the wood products industry, terahertz (THz) radiation is showing promise for new types of sensing and imaging applications, which depend on the ability of THz radiation to probe the gross fiber structure of wood. The sensitivity to this gross fiber structure is a result of the strong birefringence of wood at THz frequencies. Wood is a complex structure, and the large birefringence observed may be due to either intrinsic or form birefringence. In this paper, the origin of birefringence in wood at THz frequencies is examined in detail. Although the source of birefringence varies according to species, the trend shows contributions from both types of birefringence. This has implications for application development in the wood products industry, where the possibility of probing both the gross physical structure of wood and wood products, and the intrinsic properties of wood such as crystallinity and microfibril angle, simultaneously may allow for nondestructive noncontact strength testing of wood and composite wood products.

Birefringence of wood at terahertz frequencies

Fibre content of solid wood plays an important role in the wood products industry in terms of value. Additionally, fibre structure in composite wood products such as Oriented Strand Board (OSB) and paper products plays an important role in terms of strength properties. The effect of moisture content on wood properties is important in the manufacturing process and final product performance, and therefore its effect on the birefringence is of considerable interest. Since solid wood exhibits strong birefringence at terahertz frequencies, there may be potential applications of terahertz spectroscopy to fibre content and structure sensing. There are two potential sources for this strong birefringence: (i) form birefringence resulting from the porous structure of solid wood and (ii) intrinsic birefringence resulting from the dielectric properties of the material itself. In this report, the variability of birefringence within and between species, the dependence of the birefringence on moisture content and the relative contributions from form and intrinsic birefringence are examined. In order to clarify the role of these contributions to the measured birefringence, polarized terahertz reflection spectroscopy is examined and compared to the results obtained in a transmission geometry. Comparison of the birefringence measured in transmission and reflection geometries suggests that form birefringence may dominate.

The Acoustic Properties of Water Submerged Lodgepole Pine (Pinus contorta) and Spruce (Picea spp.) Wood and Their Suitability for Use as Musical Instruments

Wood is a common material used for the manufacture of many products, and submerged wood, in particular, has been used in niche markets and musical instruments. In order to examine if submerged wood in British Columbia, Canada, would be appropriate for use as musical instruments, a study was performed in 2007 on submerged wood from Ootsa Lake, British Columbia, Canada. The results of that study showed the wood was not suitable for musical instruments. In this paper, the wood samples were allowed to age untouched in a laboratory setting and were then retested under the hypothesis that physical acoustic characteristics would improve. It was shown, however, that acoustic properties became less adequate after being left to dry over time. This article describes the density, speed of sound, acoustic constant and characteristic impedance properties for submerged wood and a comparison is made for different applications for musical instruments.

1H Nuclear Magnetic Resonance of Lodgepole Pine Wood Chips Affected by the Mountain Pine Beetle

In this study, wood-water interactions of mountain pine beetle affected lodgepole pine were found to vary with time since death. Based on an analysis of magnetization components and spin-spin relaxation times from 1H NMR, it was determined that the mountain pine beetle attack does not affect the crystalline structure of the wood. Both the amorphous structure and the water components vary with time since death, which could be due to the fungi present after a mountain pine beetle attack, as well as the fact that wood from the grey-stage of attack cycles seasonally through adsorption and desorption in the stand.

Evaluation of Compatibility between Beetle-Killed Lodgepole Pine (Pinus Contorta var. Latifolia) Wood with Portland Cement

The compatibility of wood from mountain pine beetle (Dendroctonus ponderosa) killed lodgepole pine (Pinus contorta var. latifolia) with Portland cement was investigated based on time-since-death as a quantitative estimator, and the presence of blue-stained sapwood, brown rot, or white rot as qualitative indicators. The exothermic behavior of cement hydration, maximum heat rate, time to reach this maximum, and total heat released within a 3.5–24 h interval were used for defining a new wood-cement compatibility index (CX). CX was developed and accounted for large discrepancies in assessing wood-cement compatibility compared to the previous methods. Using CX, no significant differences were found between fresh or beetle-killed wood with respect to the suitability for cement; except for the white rot samples which reached or exceeded the levels of incompatibility. An outstanding physicochemical behavior was also found for blue-stained sapwood and cement, producing significantly higher compatibility indices.

Terahertz applications in the wood products industry

Abstract: An overview of terahertz (THz) technology for the wood products industry is presented. The basic application areas that are amenable to exploiting emerging THz technology are examined. In doing so, the basics of wood structure are presented so that THz–wood interactions can be discussed. This will set the context for discussing a THz scanner that was deployed in a successful pilot study in 2008, which measured oriented strand board (OSB) mat density in the production process, and allowed mill operators to adjust the process based on real-time feedback provided by the THz scanner.

The Differential Thermal Response of Knots and Clear Wood Following Rapid Heating

This study correlated the differential clear wood versus knot wood thermal response to rapid heating for 12 wood species to differences in specific gravity, equilibrium moisture content, extractives content, and microfibril angle. It was found that the relative levels of these variables explain much of the observed difference in clear vs. knot wood temperature following rapid heating. Rapid heating resulted in cooler knot wood temperatures which differ from hotter knot wood temperatures found by previous researchers for longer-term heating.