Extraction of terahertz wave parameters that characterize woollen clothes

Wool is a natural fiber with a high price, making it practical in the recycled fiber market. To reduce the cost of sorting fibers, terahertz waves have been used to extract parameters within the spectral information that is characteristic of wool fiber. Differences due to the specific surface shape (scale shape) and the terahertz measurement area were utilized for the identification. Characteristic features of wool content were observed between 19.4 THz and 19.8 THz by Fourier transform infrared spectroscopy measurements. At 19.5 THz, the reflectance decreased from 2.0% to 0.85% as the wool content increased. This is due to the scale shape of the wool surface causing scattering. Samples with more than 80% wool could be identified by 1.4% or less reflectance at this frequency. A mathematical expression for a reflectance that decreases as the wool content increases can be successfully expressed as an exponential function. In addition, a correlation between the surface structure of the sample and its anisotropy due to weaving to the polarized terahertz wave was confirmed. Due to the structural characteristics of the sample, there is an anisotropy of 45° or 90° which could be identified by a transmittance of 40%.