Focal Law Sequencing
As noted previously, phased array beams are generated by pulsing the individual probe elements or groups of elements in a particular pattern. Phased array instruments will generate these patterns based on information that has been entered by the user.
Software known as a focal law calculator establishes specific delay times for firing each group of elements in order to generate the desired beam shape through wave interaction, taking into account probe and wedge characteristics as well as the geometry and acoustical properties of the test material. The programmed pulsing sequence selected by the instrument's operating software then launches a number of individual wave fronts in the test material. These wave fronts in turn combine
constructively and destructively into a single primary wave front that travels through the test material and reflects off cracks, discontinuities, back walls, and other material boundaries like any conventional ultrasonic wave. The beam can be dynamically steered through various angles, focal distances, and focal spot sizes in such a way that a single probe assembly is capable of examining the test material across a range of different perspectives. This beam steering happens very quickly, so
that a scan from multiple angles or with multiple focal depths can be performed in a small fraction of a second.
