We proposed to utilize terahertz (THz) waves for the measurement of moisture content of pulp injection molding (PIM) pellets. We developed an automatic and non-destructive THz measurement system with a 0.1 THz source, pyroelectric detector, load cell, and step motor stage. As a first step, the correlation between THz transmittance and moisture content of the PIM product was studied. The results strongly suggest that the proposed method should be applicable to moisture content analysis of PIM products with better than 1% resolution and accuracy, which is much better than the previous studies with more expensive THz sources. Since the contents of pellets and products are the same, it is possible to estimate the moisture content in the pellets by designing similar apparatus. It should be noted that this method is applicable not only to PIM but also has many other applications.

1. [1] H. Yokoi, K. Matsuzaka, and M. Maruno, “Study on pulp injection molding (Part-1 ) – Measurement of Flow Behavior of Molding Compounds Using Bar-flow Cavity and Characteristics of Molded Products –” Seikei-Kakou, Vol.22, pp. 645-651, 2012 (in Japanese).
2. [2] K. Sundara-Rajan, L. Byrd, and A. V. Mamishev, “Moisture content estimation in paper pulp using fringing field impedance spectroscopy,” IEEE Sensors J., Vol.4, pp. 378-383, 2004.
3. [3] W. J. Batchelor, Z. Q. Wu, and R. E. Johnston, “Measurement of z-direction moisture transport and shrinkage in the drying of paper,” Appita J., Vol.57, pp. 107-111, 2004.
4. [4] W. M. Seaman, W. H. Mccomas Jr., and G. A. Allen, “Determination of water by Karl Fisher Reagent,” Analytical Chemistry, Vol.21, pp. 510-512, 1949.
5. [5] R. Neimanis and R. Eriksson, “Diagnosis of moisture in oil/paper distribution cables-part I: Estimation of moisture content using frequency-domain spectroscopy,” IEEE Trans. Power Delivery, Vol.19, pp. 9-14, 2004.
6. [6] W. L. Chan, J. Deibel, and D. M. Mittleman, “Imaging with terahertz radiation,” Rep. Prog. Phys., Vol.70, pp. 1325-1379, 2007.
7. [7] M. Tonouchi, “Cutting-edge terahertz technology,” Nature Photonics, Vol.1, pp. 97-105, 2007.
8. [8] H. Yoshigoe, S. Kadoya, S. Takahashi, and K. Takamasu, “Fabrication and composition control of three-dimensional dielectric metal microstructure using photocatalyst nanoparticles,” Int. J. of Automation Technology, Vol.8, pp. 523-529, 2014.
9. [9] C. Jördens, S. Wietzke, M. Scheller, and M. Koch, “Investigation of the water absorption in polyamide and wood plastic composite by terahertz time-domain spectroscopy,” Polymer Testing, Vol.29, pp. 209-215, 2010.
10. [10] D. Banerjee, W. von Spiegel, M. D. Thomson, S. Schabel, and H. G. Roskos, “Diagnosing water content in paper by terahertz radiation,” Optics Express, Vol.16, pp. 9060-9066, 2008.
11. [11] D. Grischkowsky, S. Keiding, M. van Exter, and C. Fattinger, “Far-infrared time-domain spectroscopy with terahertz beams of dielectrics and semiconductors,” J. Opt. Soc. Am. B, Vol.7, pp. 2006-2015, 1990.
12. [12] M. C. Beard, G. M. Turner, and C. A. Schmuttenmaer, “Terahertz spectroscopy,” J. Phys. Chem. B, Vol.106, pp. 7146-7159, 2002.
13. [13] K. Kawase, Y. Ogawa, Y. Watanabe, and H. Inoue, “Non-destructive terahertz imaging of illicit drugs using spectral fingerprints,” Opt. Express, Vol.11, pp. 2549-2554, 2003.
14. [14] M. Picollo, K. Fukunaga, and J. Labaune, “Obtaining noninvasive stratigraphic details of panel paintings using terahertz time domain spectroscopy imaging system,” J. of Cultural Heritage, Vol.16, pp. 73-80, 2014.