Guided Vibration
Guided elastic vibrations propagate through thin plates and membranes with boundaries that constrain the wave motion. In paper science, lamb waves are used to analyze the mechanical properties of a moving web without physical contact. These waves travel along the entire thickness of the sheet and respond to changes in density or stiffness.
Wave Mode
Two primary modes exist where the particles move either symmetrically or asymmetrically relative to the center of the plate. The velocity of lamb waves depends on the frequency of the excitation and the specific elastic constants of the paper grade. By measuring the time of flight between two points, sensors calculate the modulus of elasticity in both the machine and cross directions.
This non-destructive approach allows for continuous quality control on the paper machine. Advanced algorithms distinguish between the different modes to provide a detailed map of the sheet structure.
Material Feedback
Information gathered from the wave propagation helps operators adjust the refining or pressing sections to hit target specifications. Because lamb waves interact with the internal structure of the sheet, they detect flaws that surface inspections might miss. Modern transducers operate in the ultrasonic range to avoid interference from the audible noise of the factory.
