Measurement and Analysis of Stiffness Properties in Moving Paper Using Noncontact Laser Ultrasonics, 1999 International Paper Physics Conference Proceedings

J.H. Jong, P.H. Brodeur, J.P. Gerhardstein

An experimental investigation has been conducted to measure real time paper stiffness properties on moving paper using noncontact laser ultrasonics. The generation and detection of Lamb waves by laser ultrasonics were performed previously on static paper to relate the wave phase velocity with the corresponding paper stiffness [1,2]. The current study is focused on the detection and analysis of the two fundamental Lamb wave modes, A0 and S0, on moving paper, using photo-induced electromotive force (Photo-EMF) interferometer technology [3]. As the Lamb waves propagated in the plane of paper from the generation point, the two wave modes, A0 and S0, were detected in the signal. Each mode represented different stiffness properties of paper. The S0 mode is a fast-moving fundamental dilatational mode and is used to predict longitudinal stiffness properties in any direction with respect to MD. The A0 mode is dispersive and is sensitive to out-of-plane shear stiffness properties at high frequency while the low frequency A0 mode is mostly related to bending stiffness. The A0 mode analysis is performed using an analyzing technique described by Jong et al. [2]. A new approach to resolve a correction of phase angle at low frequency is also suggested. The analysis is performed using the results obtained by a copy paper sample (80 g/m 2 ). Nevertheless, the analysis technique should be applicable to other paper grades. The sample was tested above production speeds using a web simulator developed at the Institute of Paper Science and Technology. The experimental results show that the use of on-line laser ultrasonic method is a promising technology to predict real time paper stiffness properties.