Understanding Acoustic Emission Testing- Reading 1 Part B-A

Ultrasonic and acoustic emission testing contrasted
An arbitrary mechanical excitation applied to a plate will generate a
multiplicity of Lamb waves carrying energy across a range of frequencies.
Such is the case for the acoustic emission wave.
In acoustic emission testing, the challenge is to recognize the multiple Lamb
wave components in the received waveform and to interpret them in terms of
source motion.
This contrasts with the situation in ultrasonic testing, where the first challenge
is to generate a single, well-controlled Lamb wave mode at a single frequency.
But even in ultrasonic testing, mode conversion takes place when the
generated Lamb wave interacts with flaws, so the interpretation of reflected
signals compounded from multiple modes becomes a means of flaw
characterization.
Plate or Lamb waves are similar to surface waves except they can only be
generated in materials a few wavelengths thick.
Charlie Chong/ Fion Zhang