A C-scan from a phased array system is very similar to the one from the conventional probe seen above. With phased array systems however, the probe is typically moved physically along one axis while the beam electronically scans along the other according to the focal law sequence. Signal amplitude or depth data is collected within gated region of interest just as in conventional C-scans. In the case of phased arrays, data is plotted with each focal law progression, using the programmed beam
aperture.
Below is an actual scan of the same test block showed in the previous section using an encoded 5 MHz, 64 elements linear array probe with a straight wedge or show. Each focal law uses 16 elements to form the aperture, and at each pulsing the starting element increments by one. This results in forty-nine data points that are plotted (horizontally in the image below) across the transducer's 37 mm (1.5") length. As the transducer is moved in a straight line forward, a planar C-scan view
emerges. Encoders will normally be used whenever precise geometrical correspondence of the scan image to the part must be maintained, although non-encoded manual scans can also provide useful information in many cases.
While the graphic resolution is not fully equivalent to the conventional C-scan because of the larger effective beam size, there are other considerations. The phased array system is field portable, which the conventional system is not, and costs about one-third the price. Additionally, the phased array image was made in a few seconds, while the conventional immersion scan took several minutes. Real time generation of the C-scan is shown below.
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Cross Sectional B-Scan >>