Figure 5-73 shows the principle of this method. The A-scans in the figure represent the outline of multiple echo
signals from the skin that cannot be individually resolved. This method is most sensitive to unbonds between a single
layer of skin and the adhesive layer. An unbond between the adhesive and the core or another layer of skin or a doubler
will often not produce a ringing signal, because the adhesive bonded to the top sheet dampens the signal. Because of
this limitation, it is recommended that this method be applied only when one of the other methods is not applicable. A
good application for this method is the inspection of core-to-closure-member bonds.
Figure 5-73. Ringing Method.