Application of Time-of-Flight Near-Infrared Spectroscopy to Wood with Anisotropic Cellular Structure

Abstract

The newly constructed optical measurement system, which was mainly composed of a parametric tunable laser and a near-infrared photoelectric multiplier, was introduced to clarify the optical characteristics of wood with anisotropic cellular structure on the basis of the time-of-flight near-infrared spectroscopy (TOF-NIRS). The combined effects of the cellular structure of the wood sample, the wavelength of the laser beam, and the detection position of transmitted light on the time-resolved profiles were investigated in detail. The substantial optical pathlength calculated from the time-resolved profile was outstandingly larger than the sample thickness. The substance of the wood was directly related to the time delay of light propagation. In applying TOF-NIRS to the cellular structural materials, it is very important to give attention to the difference in the light scattering within the cell wall and that caused by the multiple specular-like reflections between cell walls. The newly proposed empirical equation, considering the effects of optical parameters, could well express the wavelength and sample thickness dependency of the time delay of the peak maxima. The time-resolved profile was intensively governed by the combination of light-absorbing and -scattering conditions and the degree of anisotropy. These basic data will be essential for this system to put an in-process measurement system in the wood industry to practical use.

Optical characteristics of wood investigated by time-of-flight near infrared spectroscopy

“…(3) n w where c indicates the speed of light, and n w is the refractive index of wood (1.5) (Tsuchikawa and Tsutsumi 2002). The nominal optical path length (NOPL) should be the same as sample thickness d. From these results, a parameter of effective optical path length R E/N (Tsuchikawa and Tsutsumi 2002) is calculated:…”

“…The nominal optical path length (NOPL) should be the same as sample thickness d. From these results, a parameter of effective optical path length R E/N (Tsuchikawa and Tsutsumi 2002) is calculated:…”

“…The simulated value is obtained from the forward model that is defined by calculating the time-resolved profile as a measurement value using known absorption and scattering coefficient in advance (Okada and Delpy 2003a,b). The anisotropy factor, absorption, and scattering coefficient of wood at wavelength of 840 nm are 0, 0.04, and 6.65, respectively (Tsuchikawa et al 1996, Tsuchikawa andTsutsumi 2002). Figure 7 shows normalized simulated (solid line) and actual time-resolved profiles (broken line) at wavelength of Brought to you by | University of Arizona Authenticated Download Date | 5/30/15 7:39 AM 840 nm (ds6.0 mm, a; ds8.5 mm, b; ds11.5 mm, c; ds14.5 mm, d).…”

“…By means of TOF-NIRS, it was possible to predict both sugar and acid contents in fruits (Tsuchikawa et al , 2003Tsuchikawa and Hamada 2004). Tsuchikawa and Tsutsumi (2002) investigated the effect of anisotropy of wood fiber on the timeresolved profile, which was intensively governed by the combination of light-absorbing and -scattering condition and the degree of anisotropy.…”

Vis–NIR spectroscopy for the on-site prediction of wood properties

“…Recently, NIR spectroscopy has been used to measure several properties of wood and paper products (Thygesen and Lundquist 2000, Gindl et al 2001, Tsuchikawa and Tsutsumi 2002, Meder et al 2003, Schimleck et al 2007. The potential use of NIR as an on-site monitoring tool for manufacturing processes has been further spurred by its application in wood composite manufacture (So et al 2004).…”