A Critical-Angle Ultrasonic Technique for the Inspection of Wood Parallel-to-Grain

James R. Dickens, Donald A. Bender, Don E. Bray


The objective of this paper is to present a critically refracted longitudinal wave (LCR) technique that allows localized ultrasonic inspection of wood parallel-to-grain by accessing only a single side of the material. The LCR technique has been widely applied to other materials, but not to wood. The chief advantage of the LCR technique is that 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 LCR technique was verified using southern pine lumber. Transducer beam characteristics were examined and the influence of growth ring angle was observed. Ultrasonic wave energy was found to travel near to the inspection surface. Further, localized growth ring angle was significantly correlated to signal amplitude and frequency.


Critically refracted longitudinal waves;beam profile;growth ring angle

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