FACTORS AFFECTING ULTRASONIC MEASUREMENTS IN SOLID WOOD

The basis of the ultrasonic evaluation of the viscoelastic behaviour o f wood is associated with measurements of velocities and of attenuatio n coefficients. The dispersion equation for anisotropic solids relates the complex elastic constants, the velocities and attenuations. The n umerical significance of attenuation coefficients depends on the speci fic measurement situation. In this article we discuss the method of at tenuation measurement in wood with the through-transmission technique and we relate some experimental factors that can affect the determinat ion of attenuation coefficients. The factors affecting attenuation mea surements are related to the geometry of the radiation field, and to t he scattering and absorption of ultrasonic energy by the solid. The at tenuation coefficients increase with frequency (from 0.1 to 1.5 MHz) e ither for longitudinal or shear waves. The lowest attenuation was obta ined in the longitudinal direction and the highest attenuation was mea sured in the tangential direction.