Air Coupled Ultrasonic Guided Wave Measurement for Board Crease Integrity
Air-coupled ultrasonic guided waves quantify paperboard crease ply delamination and micro-cracking non-destructively, preventing box compression failure.
Piezocomposite Transducer
Ultrasonic Sensor
Electromechanical device composed of a piezoelectric ceramic combined with a polymer resin converts electrical energy into high frequency sound waves. The piezocomposite transducer provides a high degree of sensitivity and bandwidth for testing the internal structure of paper and board. It operates by vibrating when an electric field is applied, sending a pulse through the substrate to measure thickness or stiffness.
This construction reduces the mechanical impedance mismatch between the sensor and the air.
Material Composition
Pillars of lead zirconate titanate are embedded in a soft epoxy matrix to create the active element of the probe. In the piezocomposite transducer, this structure allows for a higher coupling coefficient and lower acoustic impedance compared to monolithic ceramics. The flexible nature of the polymer reduces internal ringing and shortens the pulse duration.
This results in a better resolution for detecting delamination or small voids in the middle ply of a folding boxboard. By varying the volume fraction of the ceramic, the manufacturer can tune the sensor to a specific frequency range. This customization ensures that the wave penetrates the full thickness of the material without being scattered by the individual fibres.
Reliable data is required for determining the modulus of elasticity in different directions of the sheet.
Signal Sensitivity
Enhanced signal-to-noise ratios allow for measurements on highly attenuative materials like recycled fibre or heavy linerboard. The piezocomposite transducer maintains its performance even when the surface of the paper is rough or uneven. It functions well.
This makes it suitable for continuous monitoring in the dry end of a paper machine.