TWI Industrial Member Report Summary 313/1986
By J L Turner
This report contains the results of an experimental study into the use of Axicon and toroidal focusing elements for improving the beam characteristics of ultrasonic transducers used in non-destructive testing (NDT). It is shown, firstly, how this technique can result in improved resolution over longer ranges than can be achieved with conventionally focused probes, and from the results obtained, a new method has been developed for characterising Axicon and toroidal focusing elements. The benefits such focusing elements offer are clearly illustrated in their application to focused shear wave angle beam probes of the type used in the assessment of weld defects. These methods of focusing can be applied across the range of ultrasonic transducers used in NDT, e.g. immersion probes and compression and shear wave contact probes. The ease with which Axicon-type focusing elements can be manufactured also opens up new possibilities for transducer design, as illustrated, for example, by their application to line focused probes for immersion and contact shear wave inspection. Such probes can be constructed (and encapsulated) using virtually identical constructional techniques to those employed in mass-produced, commercially available unfocused transducers, thereby opening up the possibility of wider exploitation within the NDT industry.