Ultrasonic Wave Attenuation Basics for Paperboard Creasing Quality
Non-destructive ultrasonic wave attenuation evaluates paperboard crease quality by measuring acoustic energy loss caused by internal shear delamination.
Wave Time of Flight
Propagation Measurement
Non-destructive acoustic characterization calculates dynamic elastic properties by recording the precise duration required for an ultrasonic pulse to travel through a known material distance. In paperboard quality testing, wave time of flight measures the transit duration of longitudinal or shear waves propagating across the in-plane directions or through the out-of-plane thickness of a paperboard sample. The recorded transit time provides the raw experimental value needed to determine acoustic velocity, which directly correlates with the dynamic elastic stiffness tensor of the cellulose structure.
Modulus Calculation
Calculating dynamic stiffness constants requires combining this temporal measurement with accurate substrate thickness and density data. When evaluating a moving paperboard web, piezoelectric transducers emit nanosecond acoustic pulses and record the precise wave time of flight across a calibrated path length. Dividing the known distance by the measured transit time gives the acoustic velocity; squaring this velocity and multiplying it by the paperboard density yields the specific elastic stiffness modulus.
Because sound travels significantly faster along oriented cellulose chains than across open pore spaces, transit time measurements in the machine direction are consistently shorter than those recorded in the cross-machine direction. Measuring out-of-plane transit times through the sheet thickness evaluates the z-directional elastic modulus, providing a reliable prediction of internal bond strength without requiring destructive Scott bond testing.
Sensor Optimization
High-speed converting lines deploy non-contact laser ultrasonic or wheel-transducer arrays to monitor transit times continuously. Real-time time-of-flight tracking identifies localized stiffness variations, fibre orientation misalignment, and structural web anomalies prior to high-speed die-cutting and folding operations.