Research on Ultrasonic Imaging for Arbitrarily Shaped Interface Based on Virtual Source

When the components with arbitrarily shaped are detected by the ultrasonic imaging test, the coupling medium such as immersion or wedge is unavoidable used for ensuring the coupling condition. In this state ultrasonic wave will propagate in the arbitrarily shaped two-media interface between coupling medium and component. For the traditional ultrasonic imaging method which the sound velocity is considered constant, the above condition would cause the wrong position of defects in the image. To overcome the problem, a method combining virtual source (VS) and synthetic aperture focusing technique (SAFT) was applied. Firstly, the sound propagation time of the first interface echo of each elements were measured. Then a series of virtual sources at the two-media interface were created by the time of flight (TOF) of two consecutive elements. Secondly, in virtue of the virtual sources, the two-segment sound propagation path from emitting elements to virtual sources and from here to focus points were respectively calculated. Last each point of the imaging region was focused by the delay and sum process of SAFT. The result showed the defect location of component were displayed accurately in the VS-SAFT image.