Acoustic Scan
Propagation velocity governs how guided lamb waves travel through composite paperboard laminates during continuous production runs. Ultrasonic transducers inject high frequency mechanical stress pulses into moving webs to map hidden delaminations or structural thinning without contact. Transducer arrays mounted above the web launch Lamb waves into the substrate while receiving echoes from internal voids.
Signal attenuation profiles reveal bonding anomalies between layers as the material passes the inspection station. Frequency selection dictates penetration depth across heavier corrugated boards and delicate linerboards alike. Calibration routines adjust for varying moisture content prior to testing because baseline velocity shifts with humidity.
Signal Attenuation
Wave amplitude decays predictably as energy disperses through fibrous networks with uneven density. Defect detection relies on measuring energy loss relative to an undamaged reference standard established during setup. Scattering increases when high frequency wave fronts strike dispersed filler particles within the cellulose matrix.
Receiver sensitivity thresholds isolate true structural flaws from ambient mill vibration and roller noise. Microscopic air pockets trap acoustic energy and diminish transmission across the laminated interface.
Velocity Dispersion
Phase velocity varies continuously with excitation frequency and plate thickness across high speed converting lines. Mathematical dispersion curves correlate observed wave speeds directly with caliper measurements and structural stiffness parameters. High frequency modes concentrate energy near outer surfaces to detect skin cracks and coating flaws.
Low frequency modes penetrate the core of thick paperboard to verify internal bonding strength. Ultrasonic monitoring systems track these velocity shifts automatically to maintain strict caliper tolerances on finished products.
