Virtual source aperture image processing methods for non-destructive testing

Until recently, the processing of ultrasonic array data has been based on parallel transmission strategies enabling beam forming to occur within the material, with summing of the time domain signals performed in hardware on reception. These time domain signals are then typically stacked in software to produce B-scan images. Since the introduction of full matrix capture there has been advancement in post-processing algorithms, allowing for fully-focused inspections to be undertaken by dividing the area to be inspected into a grid of pixels and treating each as a focal point (the total focusing method). However, due to the large number of time domain signals associated with this approach, processing speed is often a limiting factor. Virtual source aperture (VSA) is an ultrasonic technique in which a highly divergent beam is generated using a focal law to simulate emission from a virtual point positioned some distance behind the transducer. When combined with each element of the array acting as a receiver, sufficient time domain signals may be acquired to allow B-scan images to be generated in real-time. In this paper, various imaging algorithms are presented, where the ability to image a series of point-like reflectors is demonstrated. Due to its high data acquisition speed, low computational requirement and reduced data size, VSA is shown to offer significant performance advantages over other advanced ultrasonic techniques, such as FMC