Jr. Dickens et al., A CRITICAL-ANGLE ULTRASONIC TECHNIQUE FOR THE INSPECTION OF WOOD PARALLEL-TO-GRAIN, Wood and fiber science, 28(3), 1996, pp. 380-388
The objective of this paper is to present a critically refracted longi
tudinal wave (L(CR)) technique that allows localized ultrasonic inspec
tion of wood parallel-to-grain by accessing only a single side of the
material. The L(CR) technique has been widely applied to other materia
ls, but not to wood. The chief advantage of the L(CR) technique is tha
t ultrasonic waves can be transmitted through wood at frequencies much
higher than previously possible (up to 1.5 MHz), leading to potential
gains in sensitivity over lower frequency methods. The L(CR) techniqu
e was verified using southern pine lumber. Transducer beam characteris
tics were examined and the influence of growth ring angle was observed
. Ultrasonic wave energy was found to travel near to the inspection su
rface. Further, localized growth ring angle was significantly correlat
ed to signal amplitude and frequency.