Terahertz-based identification of waste paper for improved recycling in Japan

The identification of different types of wastepaper is important during recycling. In this study, we demonstrate the effectiveness of nondestructive diagnostic testing using terahertz waves. Seven types of paper, including contraband paper, were irradiated with terahertz waves of multiple frequencies over a wide bandwidth, and their transmission characteristics evaluated and contrasted. The experimental results show a negative correlation between the basis weight of the samples and the transmittance of paper pulp, which allows to identification of paper pulp types. These results suggest that terahertz waves can be an effective method for identifying different types of paper pulp. Based on these results, we believe that Terahertz transmission measurements can significantly contribute to the improved recycling of recovered paper resources.