Park, Choon-Su; Korea Research Institute of Standards and Science; Korea
Kim, J.-W.; KHNP Central Research Institute; Korea
Park, C.-S.; Korea Research Institute of Standards and Science; Korea
Session: Imaging - UT 2
Time: 09:40 - 10:00
It has been developed to improve spatial resolution of beamforming images with a phased array transducer. Cross-spectral beamforming is a promising way to make the resolution better by obtaining spatial impulse response, which is called point spread function or array pattern, from cross-spectral matrix. In particular, closed cracks are hardly detected by conventional ultrasonic testing, since most incident ultrasound passes through them thoroughly. Nonlinear ultrasound inspection using sub-harmonic frequency has been proved to be a promising way to detect the closed cracks. In addition, sub-harmonic phased array (PA) was proposed to visualize how far the closed cracks stretch out in solids. The sub-harmonic PA generally consists of a single transmitter and an array receiver to catch sub-harmonic waves generated from closed cracks. Oblique incidence for boosting sub-harmonic generation inevitably gives rise to various surface waves that contaminate the signals measured in the receiving array. The surface wave interference often degrades PA images severely, and then it is difficult to read closed crack position from the images. There might be various ways to prevent or get rid of the interference. In particular, Enhancing images by signal processing could be a highly cost-effective way. In other words, periodic patterns distributed in a PA image are a most frequent interference induced by surface waves, and they could be properly removed by spatial frequency filtering. Experiments clearly ensure that the spatial frequency filter improves PA images easy to delineate closed cracks.