THz Properties of Typical Woods Important for European Forestry
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THz Properties of Typical Woods Important for European Forestry K. Krügener 1 & S. Sommer 2 & E. Stübling 2 & R. Jachim 1 & M. Koch 2 & W. Viöl 1 Received: 4 February 2019 / Accepted: 13 May 2019 / Published online: 6 June 2019 # The Author(s) 2019
Abstract Terahertz (THz) properties of seventeen types of wood typically growing within the European area are investigated. The samples include both coniferous and deciduous timbers. The determined properties can be useful for further THz studies on samples consisting completely or partially of wood, for example, art objects. Especially in the field of art conservation, THz spectroscopy is an excellent non-destructive evaluation method, which shows considerable analysis potential. Keywords THz spectroscopy . Wood . Coniferous . Deciduous For many centuries, wood has been one of the most used basic materials to construct furniture or buildings. In addition, many important art objects have been made out of wood. Considering the value and uniqueness of such objects, the use of non-invasive methods is desired for the investigation of these objects. THz spectroscopy has this non-invasive character. However, only a few THz studies on wood exist. For example, damage or moisture has been examined on lumber [1, 2], and also, the possibility of tree ring and wood density analysis has already been demonstrated [3–6]. The wood structure is partly of the same dimension as the THz wavelengths. This will lead to scattering of the THz waves; a fact that could make potential applications difficult, as the attenuation of THz waves could be caused by scattering or absorption. As this cannot be distinguished through a simple transmission or reflection measurement, the “real” dielectric parameters will be affected with an uncertainty. This could complicate experiments where knowledge of the dielectric properties of wood is crucial. Possible THz applications on wooden objects include, for example, THz tomography on panel paintings or feeding damages on wood [7, 8]. In order to be able to estimate the success of such an application and to be able to tomographically reconstruct the THz data, knowledge
* K. Krügener [email protected]
1
Faculty of Natural Sciences and Technology, HAWK University of Applied Sciences and Arts, Von-Ossietzky-Str. 99, 37085 Goettingen, Germany
2
Department of Physics, Philipps-Universität Marburg, Renthof 5, 35032 Marburg, Germany
Journal of Infrared, Millimeter, and Terahertz Waves (2019) 40:770–774
771
of the refractive index and the absorption coefficient in the THz range of the involved materials is important. Here, we study the THz properties of different wood specimens in the THz range using THz time-domain spectroscopy in transmission geometry. The samples selected are typical timber materials of trees growing within the European area. They are commonly used for art objects, furniture, as well as construction materials for buildings. Based on this data, we can estimate the application potential of THz radiation for the investigation of wooden ob
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