Examination of objects made of wood using air-coupled ultrasound

Abstract

The authors describe an experimental air-coupled, ultrasonic measurement system that can be used to study the propagation of megahertz signals in wooden plates ranging in thickness from 3 to 25 mm. They also report experimental measurements of the amplitude of transmitted, narrowband, 0.5-MHz signals as a function of the angle of incidence for different grain orientations. They compare the experimental results for balsa and poplar with results obtained on plates made of polymethyl methacrylate (PMMA). They interpret the results using a slowness-surface approach.<>