Air-coupled ultrasonic assessment of wood veneer.

Air-coupled ultrasound (ACU) provides a tool to evaluate wood samples of small or moderate thickness (<30 mm) thereby avoiding direct contact or liquid coupling. Results of through-transmission ACU measurements on wood veneer samples and related products are reported with respect to a wide variety of quality aspects. Fluctuations in the averaged received signal levels appear to be correlated to the presence of natural or machine-induced thickness and density variations, flaws and grain damage, errors produced by the manufacturing process, insufficient bonding on a substrate, etc.

Recent observations with air-coupled NDE in the frequency range of 650 kHz to 1.2 mHz.

An air-coupled NDE-system has been used for the inspection and imaging of discontinuities and inhomogenities in different kinds of materials, such as coating variations on tissue, spot welds on steel, and air inclusions in metal plates and welds. The measurement system operates in either continuous or pulse mode at sound frequencies between 0.65 and 1.

On the polarization of light diffracted by ultrasound.

If light is diffracted by ultrasound in an isotropic medium with acoustically induced birefringence, the state of polarization is modified in each order of diffraction with respect to the initial state of polarization of the incident light wave. In the present paper, some polarization effects are discussed in the case of normal light incidence. In general a rotation of the main polarization plane occurs, together with a change of the ellipticity.