Recognition of geometric echoes in ultrasonic hollow axle testing

Ultrasonic testing is based on mechanical waves above 20 kHz. Unlike electromagnetic waves, sonic waves can only propagate in a medium with particles like solid state bodies, fluids or gas. A vacuum contains no particles and therefore no wave propagation is possible. Based on this fact, I will first give an overview of particle movement in a solid state body, refraction on a bounding surface and mode conversion. Technical implementation details like construction and operation of transducer and transceivers or the measurement chain will be skipped by me for reasons of number of pages and could be reffered in