Macroscopic Considerations of Ultrasonic Propagation in Wood - Attenuation

Measurement of ultrasonic longitudinal and transverse transmittion loss have been made on specimens of Horse Chesnut, Maple and Norway Spruce. Five frequencies between 100kHz and 1.5MHz were chosen, while the direction of propagation of the waves was varied in seven equal steps between the principals axes of the wood in each of the three principal planes. The problem of mode conversion, interference, transduction, and phase cancellation require the measurements along the principal axes to be interrupted with great care, while the lack of pure mode propagation off-axis can enhance these problems. Nevertheless differing frequency and angular responses were foung for the different species, with the loss increasing with frequent being typically in the range 12-30 (or more) dB/cm in this frequency range.