OUT-OF-PLANE ULTRASONIC TESTING OF PAPER MATERIALS USING FLUID-FILLEDRUBBER WHEELS

A dry-contact ultrasonic technique using two fluid-filled rubber wheel s is used to probe the thickness and Z-direction sound traveling time in paper materials. The Z-direction longitudinal velocity and specific stiffness are determined from these raw measurements. In addition to time domain measurements, frequency domain analysis of ultrasonic puls es is used to evaluate the dispersion and attenuation of sound in the Z-direction. Since these phenomena depend upon the dimensions of sound scattered sites inside a material, they can be used to further probe down the fibrous and porous structure of paper. The fluid-filled wheel s technique can also be used to investigate the reflection of sound on both sides of paper, and establish a relationship to surface roughnes s. Results are presented for fine papers, corrugating mediums, liner b oards, and heavy hoards. The potential of the technique for off-line a nd on-line monitoring of various paper physical properties is discusse d.