Backwall Echo Attenuation 

BEABackwall Echo Attenuation is a flaw detection technique applied in ultrasonics to identify or confirm the presence of defects by observing a reduction in the amplitude of the echo reflected from the backwall. A typical example is in the inspection of forgings using a 0° probe. The amplitude of the echo from the backwall will remain approximately constant in clean material. The presence of defects between the probe and the backwall reduce the amount of sound reaching the backwall and, consequently, reduce the size of the backwall echo.

Planar laminar defects are likely to produce direct pulse-echo responses, which can be detected as signals observed in the range between the probe and the backwall echo. The BEA provides confirmation of the presence of such defects. Clusters of small defects, such as porosity, may not produce a reflected signal of sufficiently high amplitude to be detected by direct pulse-echo. However, depending on the number and density, they may scatter the sound sufficiently to be detected by BEA.

BEA is offered as a function on some flaw detectors. For an inspection of a forging, the flaw detector gain, required to detect the signals from potential defects, will be sufficiently high such that the backwall signal will be significantly greater than full-screen height. The BEA function allows a separate lower gain to be applied to a gate towards the end of the timebase, so that the backwall echo can be fully observed on the screen during the inspection and any changes in amplitude can be monitored.

For more information on BEA see:
The instruction manuals for flaw detectors offering the BEA function.

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