What does a typical back-wall echo indicate in a defect-free region?

What does a typical back-wall echo indicate in a defect-free region?

• A. Reflection from the near surface.
• B. Reflection from the far surface.
• C. A signal from an internal flaw.
• D. Electronic noise.

Answer: (B)

The back-wall echo is the reflection coming from the far surface of the material. When the ultrasonic pulse travels through the piece and reaches the far boundary, it reflects back to the transducer, producing this echo. In a defect-free region, this signal appears as a clean, discrete peak after the initial near-surface reflection and is typically the strongest signal used to determine the piece’s thickness because it represents the wave traveling to and from the far boundary without being interrupted by internal flaws. If there were a flaw inside, you’d expect additional echoes within the path or a distorted back-wall signal; a true electronic noise pattern would be irregular and not tied to the material’s boundaries.

The back-wall echo is the reflection coming from the far surface of the material. When the ultrasonic pulse travels through the piece and reaches the far boundary, it reflects back to the transducer, producing this echo. In a defect-free region, this signal appears as a clean, discrete peak after the initial near-surface reflection and is typically the strongest signal used to determine the piece’s thickness because it represents the wave traveling to and from the far boundary without being interrupted by internal flaws. If there were a flaw inside, you’d expect additional echoes within the path or a distorted back-wall signal; a true electronic noise pattern would be irregular and not tied to the material’s boundaries.