FACTORS AFFECTING ULTRASONIC MEASUREMENTS IN SOLID WOOD

The basis of the ultrasonic evaluation of the viscoelastic behaviour of wood is associated with measurements of velocities and of attenuation coefficients. The dispersion equation for anisotropic solids relates the complex elastic constants, the velocities and attenuations. The numerical significance of attenuation coefficients depends on the specific measurement situation. In this article we discuss the method of attenuation measurement in wood with the through-transmission technique and we relate some experimental factors that can affect the determination of attenuation coefficients. The factors affecting attenuation measurements are related to the geometry of the radiation field, and to the scattering and absorption of ultrasonic energy by the solid. The attenuation coefficients increase with frequency (from 0.1 to 1.5 MHz) either for longitudinal or shear waves. The lowest attenuation was obtained in the longitudinal direction and the highest attenuation was measured in the tangential direction.