Appendix C – Glossary
Part # 910-250C
165
Appendix C – Glossary
Term Definition
Acoustic Impedance A material property defined as the product of sound
velocity (C) and the material’s density (d).
Acoustic Interface The boundary between two media of different acoustic
impedance.
Acoustic Zero The point on the CRT display that represents the entry
surface of the specimen.
Amplifier An electronic device that increases the strength of a
signal fed into it by obtaining power from a source
other than the input signal.
Amplitude Referring to an indication on the CRT screen, the
vertical height of an indication measured from the
lowest to the highest point on the indication. In wave
motion, the maximum displacement of the particles of
the material.
Angle Beam Transducer A transducer that transmits or receives the acoustic
energy at an angle to the surface to set up shear waves
or surface waves in the part being inspected.
A-Scan Pulse-echo format wherein the CRT display shows the
pulse travel time in the horizontal direction (left to
right) representing the corresponding sound paths. The
vertical direction (bottom to top) displays the
maximum value of the acoustic pressure echo
amplitude received by the probe.
Attenuation The loss in acoustic energy that occurs between any
two points of travel. This loss may be due to
absorption, reflection, and other phenomena.
Attenuation (M.L.A.) The loss of sound pressure in a travelling wavefront
caused by the scattering of some of the wave’s sound
pressure by the grain structure and/or porosity of the
medium, and by absorption, a conversion of sound
energy into heat.
Back or Backwall Echo The echo received from the side of the specimen
opposite the side to which the transducer is coupled.
This echo represents the thickness of the specimen at
that point.
Background Noise Extraneous signals caused by sources within the
ultrasonic testing system and the material being tested.
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