Model-Based Characterization of Planar and Focused Immersion Ultrasonic Transducers

摘要

Advanced ultrasonic nondestructive evaluation techniques require well characterized transducers. This need may arise, for example, because modern, cost-efficient fabrication procedures necessitate high reliability inspection through non-planar surfaces and for which careful control of the beam pattern in needed. An example of this is the developing procedure for inspection of titanium billet material for subtle flaws, such as hard-alpha inclusions [1]. Large aperture, bicylindrical focusing transducers are being developed, and characterization procedures are also being formulated for that activity. Methods are required to relate design parameters, such as crystal and lens shape, to the ultrasonic fields that will be generated in the billet. Advanced signal processing methods, such as characterization of noise due to ultrasonic scattering from grains, require precise knowledge of probe characteristics, as well. For example, model-based approaches to calculating a grain scattering “figure of merit” [2] require the ability to deconvolve transducer effects from measured noise signals. Knowledge of transducer characteristics is also essential for the application of ultrasonic measurement models [3,4] to the prediction of flaw signal amplitudes as measured through curved component surfaces and in a variety of materials. This geometry and material transferrability issue is of great importance in new methods applied to designing for inspectability.