Knowledge

Угловой S-скан

Of all imaging modes discussed so far, the Sectorial scan is unique to phased array equipment. In a linear scan, all focal laws employed a fixed angle with sequencing apertures. Sectorial scans, on the other hand, use fixed apertures and steer through a sequence of angles.

Two main forms are typically used. The most familiar, very common in medical imaging, uses a zero degree interface wedge or shoe to steer longitudinal waves at relatively low angles, creating a pie-shaped image showing laminar and slightly angled defects.

The second format employs an angled plastic wedge to increase the incident beam angle for generation of shear waves, most commonly in the refracted angle range of 30 to 70 degrees. This technique is similar to conventional angle beam inspection, except that the beam sweeps through a range of angles rather than a just single fixed angle determined by a wedge. As with the linear scan, the image presentation is a cross-sectional picture of the inspected area of the test piece.

The actual image generation works on the same stacked A-scan principle that was discussed in the context of the linear scans introduced in the previous section. The end user defines the angle start, end, and step resolution to generate the sectorial image. You will notice that the aperture remains constant, with each defined angle generating a corresponding beam with characteristics defined by aperture, frequency, damping and the like. The waveform response from each angle (focal law) is digitized and plotted related to color at the appropriate corresponding angle, building a cross sectional image.

In actuality, the sectorial scan is produced in real time so as to continually offer dynamic imaging with transducer movement. This is very useful for defect visualization and increases probability of detection, especially with respect to randomly oriented defects, as many inspection angles can be used at once.

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Combined Image Formats >>