High Frequency Acoustic Profiling for Multilayer Board Barrier Integrity
Inline high-frequency acoustic profiling measures micro-scale barrier delamination and polymer layer thickness across dynamic paperboard converting webs.
Acoustic Scattering Loss
Physical Origin
Reduction in the energy of a high frequency sound wave as it passes through a paper or board substrate occurs due to the structural boundaries within the sheet. This phenomenon of acoustic scattering loss occurs when the ultrasonic wave encounters fibers and microscopic air pockets that redirect the energy away from the receiver. Such dispersion prevents the wave from propagating in a straight path, indicating the degree of internal uniformity.
High density sheets show minimal disruption of the signal.
Measurement Protocol
Evaluation of the energy reduction requires a pair of ultrasonic transducers positioned on opposite sides of the moving web or paper sample. Instrumentation calculates the difference between the emitted signal amplitude and the received signal amplitude to determine the acoustic scattering loss in decibels. This measurement depends on the frequency of the sensor and the caliper of the paperboard.
Converting Influence
Control of the internal structure of paperboard ensures that subsequent converting steps like creasing and folding proceed without unpredictable cracking. Fluctuations in the acoustic scattering loss correlate with variations in internal bond strength and fiber alignment, which directly affect the stiffness of the material. If the scattering is too high, the paperboard may possess excessive air voids that weaken the structural integrity during mechanical manipulation.
Converting plants monitor these values to maintain uniform folding resistance across different batches of paperboard. By keeping the signal drop within specified limits, the risk of delamination on the folder gluer is minimized.