Abstract
About the ultrasonic reflection behaviors at micro air gap several papers had been discussed using optical Newton's ring specimen. However quantitative behaviors of ultrasound at the micro gap remain unsolved until now. Since these behaviors directly relate to the accuracy of the ultrasonic crack sizing and also to the basic behaviors of subharmonic wave. Using highly focused acoustic lens with the quantitative performances of spatial resolutions and accurate experimental setups, we investigate the accurate ultrasonic behavior at the micro gap in this study. As a result, ultrasonic transmission began to occur with 60-70 nm air gaps for all the measurements which relate to the surface roughness of contact glass plates. Using this micro gap specimen, we also investigated the subharmonic imaging of micro gap. However the subharmonic image was not able to be obtained.
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