Development of a Method for Non-Destructive Diagnosis of Near Surface Defects Using the Phase of Ultrasonic Echoes

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  • 超音波エコーの位相を用いた物体表面近傍の異常診断法の開発

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<p>In non-destructive testing using ultrasound, a reliable signal processing method which separates the superimposed echoes is needed to detect defects. In this study, we propose a new signal processing method using the phase of ultrasonic echoes. When defects are located near the surface of the inspected object, it is difficult to detect defects because the echoes reflected by the defect are superimposed on ones reflected by the surface of the inspected object. To separate the superimposed echoes, the authors focused on points on the phase distribution of the wavelet transform of the echoes. This point can be used to estimate the location and size of defects, but its applicability is limited. However, there is not theoretically the limitation when using the short-time Fourier transform. In this paper, some samples with a hole were prepared and superimposed echoes were measured by using ultrasonic waves. The depth and diameter of the hole were estimated by applying wavelet transform and short-time Fourier transform to the superimposed echoes. It provides that the use of the short-time Fourier transform enabled estimation over a wider range.</p>

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