What is meant by "differential focusing" in phased array ultrasonic testing (PAUT)?

Differential focusing in phased array ultrasonic testing (PAUT) refers to techniques that adjust the focal length dynamically to enhance defect detection at various depths within the test material. This method allows for the manipulation of the focal point of the ultrasonic beam, enabling the inspection of areas that may be at different depths from the probe. By focusing the sound waves precisely at different depths, the technician can improve the sensitivity to flaws, ensuring better detection and characterization of defects.

Using this focusing approach is crucial in applications where materials have varying thicknesses or where defects may lie at different depths. It enhances the ability to capture clear echoes from defects, leading to a better evaluation of their size and nature.

Contrarily, relying on a fixed focal length would limit the inspection's effectiveness, especially if defects occur at various depths. Techniques that depend solely on operator skill may introduce inconsistencies and biases, making mathematical or algorithmic methods more reliable. Measuring defect sizes does not pertain directly to differential focusing but could be a result of its application.