Multiple virtual source aperture imaging for non-destructive testing

Virtual source aperture image processing methods for non-destructive testing

“…When combined with a 'receive on elements' strategy, sufficient time domain signals may be acquired to allow for the generation of fully-focused imagery [3] . For an array of N elements, VSA requires just a single ultrasonic transmission, with N time domains collected.…”

“…VSA may be used to acquire data with a single transmission, or a sub-aperture defined to allow for linear or angular sweeping over the array [3] . The latter allows for additional time domain signals to be acquired by synthesising a virtual array from a series of virtual point sources.…”

“…It is a trivial step to expand these equations to work through a refractive boundary by considering Fermat's principle of least time [3] . Accounting for the refractive boundary allows for VSA to be used for practical weld inspections, immersion testing and to compensate for the geometry of an irregular profile.…”

“…While some compromise in image quality in terms of SNR may be present with regards to a comparison of VSA+TFM and FMC+TFM, some improvement can be achieved with additional signal processing [7] or through additional VSA firings [3] .…”

“…Previous work has sought to address this issue by limiting transmission cycles [2] . By combining a phased array-type transmitting strategy (where all elements transmit in parallel to a predefined focal law) with an FMCtype receive strategy (where all elements receive data individually), VSA has the advantage of limiting the transmission cycles significantly compared to those of FMC, PAUT and conventional ultrasound, while allowing sufficient time domain information to be captured to facilitate in the generation of fully-focused ultrasonic imagery [3] . Unlike PAUT, focusing is not carried out within the material; instead an unfocused divergent beam is transmitted.…”