Ultrasonic retrieval of anisotropic stiffness tensor for trees

Acoustic non-destructive testing techniques have been developed to measure properties, such as stiffness, of standing trees and logs. Previous work using this technique to measure the stiffness of standing trees provides results that are biased towards the outerwood stiffness, which is higher than the average through the cross-section of the stem. In this paper, we explore a multipath acoustic technique for measuring components of the anisotropic stiffness matrix of tree stems, which describes the mechanical properties of wood. This technique uses anisotropic ultrasonic wave propagation velocity measurements made across a log, allowing calculation of an average stiffness through the log’s cross-section. This result was compared with those obtained using the traditional acoustic technique for standing tree and acoustic resonance techniques for logs.