US Patent 7849747 Flaw detection in exhaust system ceramic monoliths

Ultrasonic detection of flaws in ceramic monoliths such as are commonly used in diesel particulate filters is made possible by beaming ultrasound into the monolith from an inlet or outlet face thereof and analyzing the reflected ultrasound from the same face. The monolith is preferably rotated during the scan, or the scan may be repeated from several rotational positions relative to the face of the monolith. Even small flaws which are hard to detect may be identified.