City Research Online

Abstract

With the use of ultrasonic transducers, the relation between defect sizes and ranges with their echo amplitudes has been investigated both theoretically and experimentally. It is demonstrated that this relation is affected by diffraction effects which also complicate the interpretation of echo signals. These diffraction effects are interpreted in terms of compression plane and edge waves together with mode-converted shear edge waves emanating from a circular compressional transducer.

The investigation has been established with the aid of a model that predicts echo responses for flat-bottomed holes (FBH) in isotropic lossless solids interrogated by uniformly excited sources. The results predicted by the model are in good agreement with experimentally measured results obtained using commercially available wide and narrow band circular transducers.

It has been shown experimentally and theoretically that, using transducers excited with multi-cycle pulses produces large fluctuations with range in echo amplitudes for small targets. These fluctuations might results in misinterpretations of target size. The fluctuations disappear when a short pulse is used to excite the transducer.

The model is also used to obtain new distance-gain-size (DGS) diagrams that can predict the significant response variations in both the near and the far fields of a transducer. Calculated DGS diagrams have shown good agreement with experimentally obtained curves for small FBH targets positioned mostly in the near field of the transducer.

Factors like the transducer radius, excitation-pulse shape, and the method of calculating the echo amplitude have been shown to affect DGS diagrams, especially for the case of small targets in the near field. The new model provides the explanation of these effects.

A comparison between the new curves and curves produced using an earlier fluid model showed that there are significant differences between both curves, especially for small targets. Therefore, care should be taken when the fluid model is used to estimate target size in a solid medium.

Publication Type:	Thesis (Doctoral)
Subjects:	Q Science T Technology > TK Electrical engineering. Electronics Nuclear engineering
Departments:	School of Science & Technology > School of Science & Technology Doctoral Theses Doctoral Theses School of Science & Technology > Engineering

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