4.1 General Concepts of Transducer Selection
Transducer Selection
In many cases, the type of transducer used in a particular test will be determined by established inspection code or procedural requirements that the inspector needs to follow. Codes such as AWS D1.1 and ASTM E-164 detail recommended transducers and wedges, and in some cases transducer selection will be governed by past practices in the same test. If there is no code or procedure in place, then the inspector must select an appropriate transducer based on the specific test requirements, and using his or her knowledge of common test practices and general ultrasonic theory. In some cases this will involve experimentation with several different types of transducers on reference standards representing the part to be tested, to determine which one provides the best response.
The transducers used in ultrasonic flaw detection generally fall into five categories:
Once a transducer type has been selected, other important factors affecting performance are frequency, diameter, and bandwidth. These were reviewed in Section 3. Optimizing these factors in a given test often requires balancing advantages and disadvantages.
Frequency: Higher frequency transducers can resolve smaller flaws due to their shorter wavelength, while lower frequency transducers will penetrate farther in a given material because attenuation decreases with frequency.
Diameter: Larger diameter transducers can scan a given area more quickly, while smaller diameters will have better response to small reflectors and couple more efficiently into curved surfaces.
Bandwidth: Narrowband transducers have greater penetration but reduced near surface resolution, while broadband transducers have better near surface resolution but less penetration.
