Experimental measurement of acoustic guided wave propagation in logs

The stiffness of wood can be estimated using acoustic velocity. For standing trees, velocity measurements are generally obtained by driving two pikes into the tree stem, hitting one with a hammer, and measuring the time for the signal to first reach the second transducer. This time of flight method only uses the start time of the signal. This paper investigates if additional information that can be obtained from the acoustic signal could be used to measure wood properties. Wave propagation was investigated using shear transducers. These transducers were initially attached to spikes. It was found that the angle and orientation of the spikes significantly affected the received signal. Measurements were also made with transducers attached directly to the logs. The alignment of the transducers allowed different guided wave modes, such as longitudinal and torsional wave modes, to be excited and measured.