The forestry industry is a valuable part of the New Zealand economy. Timber exports rely on methods to reliably produce high quality timber | timber that is both stiff and stable. Wood is a complex, anisotropic, material in which the material properties vary considerably between species and within the same species. The New Zealand School of Forestry at the University of Canterbury is particularly interested in the selective breeding of Pinus radiata and Eucalyptus quadrangulata for the production of high quality construction timber. To assist foresters, this thesis presents improved instrumentation for the TreeTwist: a tool for the non-destructive, acoustic, time of flight measurement of stiffness and spiral grain characteristics in increment cores.

A previous iteration of the TreeTwist was hampered by electrical interference and noise issues. These issues limited the study of Eucalypts due to a higher stiffness and acoustic speed compared to Radiata pine. To remedy these issues, new, low noise electronic hardware was designed, simulated and developed for the measurement of wood stiffness using high impedance, capacitive, piezoelectric transducers. A lumped element model was used to characterise a piezoelectric accelerometer from impedance data. Using this model new stress wave generator and measurement hardware was developed. A 95V con gurable slew rate pulse generator was designed to generate stress waves while minimising electrical interference. A high impedance, high gain, low noise (3:5 nVpHz, embedded system was designed for stress wave measurement. Device driver and stress wave onset detection software was written for the TreeTwist increment core scanner.

The upgraded TreeTwist with improved instrumentation shows promise for the nondestructive, acoustic measurement of wood properties. In a study of Pinus radiata and Eucalyptus quadrangulata stiffness was measured with an estimated 7.6% stiffness measurement uncertainty.