Guided Waves, Waveguides and Mode Converted Signals

In recent years many research papers were published in NDT journals like Materials Evaluation on use of Lamb waves or plate waves in ultrasonic NDT of long and wide structures like pipe lines, airplane fuselages etc. In the research papers, these elastic waves in the ultrasonic region are described sometimes as guided waves and as waveguides at other times. Indeed they are both. However in the ultrasonic NDT literature one finds many papers where elastic waves are guided by long structures like bolts, anchor studs without dispersion like the one present in testing of pipe lines where the thickness of the pipe wall is comparable to the ultrasonic wavelength. The distinction is made in this work between the guided wave region where the characteristic dimension of the structure is much larger than the ultrasonic wavelength used for NDT resulting in no dispersion phenomenon and the waveguide region with dispersion experienced. Moreover the presence of mode converted signals producing trailing pulses in the guided wave region is discussed and their applications in the practical industrial ultrasonic NDT were presented.

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