A technical note on the relationship between ultrasonic velocity and moisture content of Brazilian hardwood (Goupia glabra)

This paper reports the application of ultrasound waves in Brazilian hardwood Goupia glabra with the purpose of evaluating the sensitivity of the ultrasonic technique to the moisture content of wood. The velocity of ultrasonic wave is sensitive to the material quality-determining factors; hence, this technique is an important industrial tool to improve the quality control of processes. The nature of the response of velocity of sound to moisture content changes in Goupia glabra led us to conclude that moisture gradients during drying have a dominating effect. The ultrasonic velocity was measured both parallel and perpendicular to the grain during drying from green to 7% moisture content. It was demonstrated that the ultrasonic velocity is sensitive to changes in moisture content of lumber during drying. The FSP can be determined analytically from data related to the velocity perpendicular to the grain and moisture content. The intersection point of the regression line calculated for moisture content variation between 7-20% and 20-55% corresponds to the FSP.