How does ultrasonic reflection testing differ from ultrasonic through-transmission testing?

In the field of nondestructive testing, ultrasonic inspection utilizes sound waves above the human hearing range to evaluate material integrity. The primary difference between reflection and through-transmission testing lies in the placement of the equipment and how the sound signal is analyzed.1

Ultrasonic Reflection Testing

In the reflection technique, both the transmitter and the receiver are located on the same side of the sample. A sound wave is sent into the material, reflects off the far side, and returns to the receiver. If the wave encounters a flaw or crack, it reflects prematurely, and the change in travel time allows for the precise mapping of the flaw's location and geometry.1

Ultrasonic Through-Transmission Testing

In the through-transmission method, the transmitter and receiver are positioned on opposite sides of the material. Instead of measuring echoes, this method monitors the passage of sound waves through the sample. Flaws are identified by detecting interruptions or attenuation in the sound signal as it travels from the transmitter to the receiver. This process often involves immersing the transmitter, sample, and receiver in a water medium.1