Ultrasonic Through-Transmission Testing
Ultrasonic testing method where transmitter and receiver are positioned on opposite sides of the component to detect reductions in acoustic energy caused by internal defects.
In through-transmission testing, you send sound waves through the component. If the sound hits a flaw like a crack or porosity, it is reflected or attenuated. From the echo, you can infer the location and size of the flaw. You always need two probes, a transmitter and a receiver. Best to place them opposite each other so the sound passes completely through the component. The coupling must be clean, so apply plenty of couplant, otherwise you lose too much sound. Choose the frequency and instrument settings based on material and wall thickness. Important: don't overinterpret the indications – not every echo is a flaw, sometimes it's just the geometry of the part.