Acoustic microscopy technique to precisely locate layer delamination

In this paper, the synthetic aperture focusing technique (SAFT) is applied to extend the depth of focus for spherically focused ultrasound transducers. This technique uses a virtual source element in the geometrical focus of the transducer. Initial experiments with a 90-mu m copper wire are conducted to investigate the efficacy of SAFT processing for positive and negative defocus. Furthermore, delamination of two glued together transparent Perspex plates is investigated. Compared to the common B-mode ultrasonic imaging that can only detect the presence of layer delamination, the proposed SAFT can accurately locate the position of delamination and visualize its extension.