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Journal of Sensors
Volume 2017, Article ID 3520967, 14 pages
https://doi.org/10.1155/2017/3520967
Research Article

Enhanced Measurement of Paper Basis Weight Using Phase Shift in Terahertz Time-Domain Spectroscopy

1School of Mechatronic Engineering, China University of Mining and Technology, Xuzhou 221116, China
2School of Information and Control Engineering, China University of Mining and Technology, Xuzhou 221116, China
3School of Electrical and Electronic Engineering, Newcastle University, Newcastle upon Tyne NE1 7RU, UK

Correspondence should be addressed to Binghua Cao; nc.ude.tmuc@auhgniboac

Received 10 February 2017; Accepted 13 April 2017; Published 16 May 2017

Academic Editor: Dzung Dao

Copyright © 2017 Mengbao Fan et al. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

Abstract

THz time-domain spectroscopy has evolved as a noncontact, safe, and efficient technique for paper characterization. Our previous work adopted peak amplitude and delay time as features to determine paper basis weight using terahertz time-domain spectroscopy. However, peak amplitude and delay time tend to suffer from noises, resulting in degradation of accuracy and robustness. This paper proposes a noise-robust phase-shift based method to enhance measurements of paper basis weight. Based on Fresnel Formulae, the physical relationship between phase shift and paper basis weight is formulated theoretically neglecting multiple reflections in the case of normal incidence. The established formulation indicates that phase shift correlates linearly with paper basis weight intrinsically. Subsequently, paper sheets were stacked to fabricate the samples with different basis weights, and experimental results verified the developed mathematical formulation. Moreover, a comparison was made between phase shift, peak amplitude, and delay time with respect to linearity, accuracy, and noise robustness. The results show that phase shift is superior to the others.