Preparatory Notes for ASNT NDT Level III Examination - Ultrasonic Testing, UT

Two significant applications of Spread Spectrum Ultrasonics are:
1. Large Structures that allow ultrasonic transducers to be "permanently"
affixed to the structures, eliminating variations in transducer registration
and couplant. Comparisons with subsequent acoustic correlation
signatures can be used to monitor critical structures such as fracture
critical bridge girders. In environments where structures experience a
great many variables such as temperature, load, vibration, or
environmental coupling, it is necessary to filter out these effects to obtain
the correct measurements of defects.
In the example below, simulated defects were created by setting a couple of
steel blocks on the top of the bridge girder.