Use of a Chirp-coded Excitation Method in Order to Improve Geometrical and Acoustical Measurements in Wood Specimen

Methods for measuring ultrasonic wave velocity in an elastic material require knowledge of the thickness of the sample. In general, the precision of this knowledge determines the accuracy of the experimental technique for measuring velocity. With the same restriction, measuring thickness of a material require a knowledge of the time-of-flight of the wave propagating. This problem is particularly acute in measuring parameters in wood specimen with an acoustical impedance contrast higher than the surrounding media. The aim of the present study was to compare chirp-coded excitation methods to determine time-of-flight, and to evaluate the precision of the measurement in function of several temporal durations. The apparent thicknesses and ultrasonic wave velocities in parallelepipedic plates of resin and wood material were measured using the method, and using, as reference, a pulse-mode approach. The relative errors of thickness measurement comparing to the results from caliper measurements are 0.1% to 6.81%. For velocity, the chirp-coded excitation method shows differences with reference method, from 0.78% to 3.64%.