Simulation on Improving Imaging Resolution of SAFT

Concrete is one of the main construction materials in civil engineering. Among the existing Nondestructive Testing (NDT) methods, the imaging techniques that can give a graphic display of the inner structure of the concrete elements have received great attention. Because of several kinds of disturbing signals in the concrete structures imaging by low frequency ultrasound, low signal-noise ratio and poor resolution are engendered. Synthetic Aperture Focusing Technique (SAFT) is one of effect methods in the ultrasonic NDT area, and can focus effectively to reflected waves, and improve the reconstructed image's resolution through rough B-scan method. For low-frequency excitation signal, however, wavepacket distortion is produced during the focusing process, which decreases test resolution. Therefore, Wavepacket Decomposition Technique (WDT), which can put the whole reflected wavepacket into focusing calculation, is introduced here to improve the reconstructed resolution. This technique solves the problem of wavepacket distortion, and better focusing effect and resolution are obtained. Furthermore, calculating velocity is increased because the points joined into SAFT calculation are cut down greatly. The presented technique has been verified by the simulation experiment. From the results, the method can improve more the ability of localizing object and give better imaging effect.