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

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.

Defect feature extraction of marine protective coatings by terahertz pulsed imaging

“…Furthermore, phase shift, which has been verified to be associated with sample thickness, can be deduced from phase spectra of sample signal and reference signal [46]. As can be seen from Fig.5 (a) and (b), although there were some differences in amplitude and phase spectrums between the four samples, it was hard to get directly the relationship between the amplitudes spectrums and coating thicknesses of the multilayered structures.…”

“…The signal had been normalized to the maximum reference signal. Usually, THz signal feature in frequency domain was extracted to help characterizing materials, such as single layer coatings [12] and paper basis weight [46]. Fig.…”

“…As can be seen from Fig.5 (a) and (b), although there were some differences in amplitude and phase spectrums between the four samples, it was hard to get directly the relationship between the amplitudes spectrums and coating thicknesses of the multilayered structures. Moreover, the phase shift method was suitable for single layer structure characterization [46], however, it is difficult to provide directly the relationship between phase shift and the four multilayered coating structures.…”

Time Segmented Image Fusion Based Multi- Depth Defects Imaging Method in Composites With Pulsed Terahertz

“…In their work, the multi-resolution statistical analysis method combining wavelet transform and principal component analysis (PCA) was presented improving the information of thermal image to distinguish defects, and the detectability of damage caused by different impact energy was discussed [3]. Fan et al proposed a noise-robust phase-shift based method to enhance measurements of paper basis weight, the result shows that is superior to the others [4]. Wang et al used advanced thermal image algorithms processing thermal data obtained by three different thermographic methods, they found that principal component analysis applied to long pulse thermography provides accurate imaging results over traditional pulsed thermography and step heating thermography [5].…”

Pencil-on-Paper Sensor for Water Detection

“…Extensive research is being carried out into the development of affordable and adaptable sensing gadgets [1][2][3][4][5]. Owing to their minimalism, affordability, and the rapidity with which they can be manufactured, paper sensors have been garnering more attention [6][7][8][9]. For instance, Gandhiraman et al are working on scalable and inexpensive single-use paper sensors for use in the field of DNA detection on the basis of chemical vapor deposition [9].…”