Progress in ultrasound lockin thermography

Ultrasound lock in thermography (UL T) is based on thermal wave imaging as a local response to periodical heat deposition. The substantial difference as compared to photothermal imaging and optical lockin thermography (OL T) is that the heat source generating a thermal wave is provided by the defect itself due to the attenuation of amplitude modulated ultrasound. While friction effects heat areas with defects selectively, the slow amplitude modulation provides a periodicity of heating that results in the emission of long ranging thermal waves from defects. This way one has a dark field method to display defects in various materials even in the presence of complicated structures related with intact samples.