Ultrasonic Properties in Woods

Abstract

Ultrasonic velocity and absorption were observed at 1∼4 MHz in nine different kinds of woods. They showed a strong anisotropic feature: the direction of growth (L) has the fastest velocity and smallest absorption; the direction perpendicular to annual rings (R) has the second; and the direction tangential to them (T) has the slowest velocity and largest absorption. The fastest velocity ranges 5000∼6000 m/s and V L : V R : V T ≃1:0.4:0.3. Absorption shows a linear increase with frequency up to 4 MHz. Velocity was also observed as a function of the moisture content of woods. It decreases rapidly with the moisture content up to a certain point around 30% and thereafter the decrease is very slow. This point gives the fiber saturation point of wood.