Back-Wall Echo
The back-wall echo is the ultrasonic signal reflected from the far surface of a test piece; its presence confirms sound transmission and its loss can indicate a major defect or coupling problem.
Definition
The back-wall echo is the first reflection from the back surface of the test piece — the signal that traveled through the full thickness and bounced back. Its time-of-flight equals 2 × thickness / velocity.
Technical Context
A strong back-wall echo confirms good coupling and a sound load path. A reduction or loss of the back-wall echo at certain positions indicates beam blockage by a large reflector — a 'loss of back-wall' indication.
Related terms
- Ultrasonic Testing (UT) — Ultrasonic Testing (UT) is an NDT method that uses high-frequency sound waves (typically 0.5–25 MHz) to detect internal flaws and measure thickness in metals, plastics, and composites by analyzing reflected echoes from a transducer.
- A-Scan — An A-scan is the basic ultrasonic display showing signal amplitude (vertical axis) versus time-of-flight (horizontal axis) from a single transducer position, used to identify, size, and locate reflectors.
- Attenuation (Ultrasonic) — Attenuation is the loss of ultrasonic energy as it propagates through a material due to absorption, scattering, and beam spread, expressed in decibels per unit path length and material-dependent.
More physics terms
Beam Spread · Near-Field · Far-Field · Dead Zone · Shear Wave · Longitudinal Wave · Surface Wave · Lamb Wave · Mode Conversion · Geometric Unsharpness
Where this comes up in practice
Terms like this one appear in three places that matter commercially: the written practice that governs how your personnel are qualified, the procedures and technique sheets that define how an examination is actually performed, and the evidence an auditor or client asks for when they want to know why an inspection was accepted. Getting the terminology right is the easy part; being able to produce the qualification record, the calibration traceability and the procedure revision that applied on the day of the inspection is the part that decides audits.
Atlantis NDT provides NDT training and certification against ASNT SNT-TC-1A and ISO 9712, ASNT Level III consulting for written practices and procedure approval, inspection management software that holds qualification, calibration and procedure-revision evidence in recoverable form, and an asset integrity platform that binds inspection results to the asset they describe. Browse the full NDT glossary or ask a Level III directly.