Laser Spectroscopy & Applied Materials Group

Laser Ultrasonics

Laser ultrasonics (LUS) is a non-contact, non-destructive method we have applied to analysis of paper mechanical properties. Ultrasound can be used to probe tensile and bending stiffness and other mechanical properties in paper. These properties correlate with the speed of ultrasonic plate waves along the paper sheet. A measurement of the time-of-flight of an ultrasonic wave over the known distance between two detection points permits determination of the propagation velocity.

To date, in order to measure stiffness using ultrasonic techniques, industry analysts have relied on measurements on samples cut from the ends of large paper rolls because measurements cannot be made on the moving sheet in the papermaking machine. Excess fiber is therfore used in papermaking to ensure that minimum stiffness specs are maintained. Otherwise, a roll of paper weighing several tons may be recycled or sold as an inferior grade if it does not meet stiffness specifications. A monitor of paper stiffness installed on the papermaking machine would allow real-time feedback control of the papermaking process, resulting in valuable savings in feedstock and energy.

• Laser material interaction generates acoustic waves (out-of-plane displacement) in material
• Wave velocity related to material properties (stiffness, thickness, density, vicosity,...)
• Non-contact, on-line, real-time measurement of physical propoerties
• Applications in paper, steel, glass, plastics,...
• Measured bedning stiffness on-line, real-time at process speed of 5000 feet/minute
• On-line LUS sensor: reduces energy and materials (pulp) use, minimizes recycling through real-time monitoring of paper properties!