Experimental analysis of surface detection methods for two-medium imaging with a linear ultrasonic array

Area of Science:

• * Ultrasonic Nondestructive Testing (NDT)
• * Acoustic Imaging
• * Materials Science

Background:

• * Accurate imaging of objects with nonplanar surfaces using ultrasonic linear array transducers requires knowledge of the object's surface shape to compensate for refraction.
• * Coupling media are essential for transmitting ultrasonic waves between the transducer and the object in immersion testing.

Purpose of the Study:

• * To propose and evaluate two new methods for detecting the surface shape of convex objects in immersion using a single ultrasonic linear array transducer.
• * To compare the accuracy and performance of these novel surface detection methods against an existing technique (pitch-catch).
• * To implement and assess a new technique for calculating delays in Synthetic Aperture Focusing Technique (SAFT) image formation based on Fermat's principle.

Main Methods:

• * Development of two surface detection methods: one based on imaging techniques and another utilizing the time-of-flight of echoes from ultrasonic signals.
• * Experimental comparison of the proposed methods with the pitch-catch method for accuracy and performance.
• * Implementation of a novel delay calculation technique for SAFT image formation, adhering to Fermat's principle, and image combination using the effective aperture technique.

Main Results:

• * The proposed surface detection methods demonstrated smaller errors in certain tested configurations compared to the pitch-catch method.
• * The novel methods exhibited slower performance relative to the pitch-catch method.
• * The developed techniques enabled interactive two-medium SAFT image formation executable on a general-purpose CPU.

Conclusions:

• * The developed surface detection and SAFT imaging techniques are effective for characterizing nonplanar surfaces in ultrasonic NDT.
• * The trade-off between accuracy and speed was observed, with the proposed methods excelling in accuracy for specific scenarios.
• * The study successfully demonstrated interactive image formation capabilities on standard computing hardware.