[논문]An Efficient Ultrasonic SAFT Imaging for Pulse-Echo Immersion Testing

Hu, Hongwei; Jeong, Hyunjo

doi:10.7779/jksnt.2017.37.2.84

An Efficient Ultrasonic SAFT Imaging for Pulse-Echo Immersion Testing 원문보기

비파괴검사학회지 = Journal of the Korean Society for Nondestructive Testing, v.37 no.2, 2017년, pp.84 - 90

Hu, Hongwei (Changsha University of Science & Technology) , Jeong, Hyunjo (Division of Mechanical and Automotive Engineering, Wonkwang University)

Abstract ▼ AI-Helper

An ultrasonic synthetic aperture focusing technique (SAFT) using a root mean square (RMS) velocity model is proposed for pulse-echo immersion testing to improve the computational efficiency. Considering the immersion ultrasonic testing of a steel block as an example, three kinds of imaging were studied (B-Scan, SAFT imaging based on ray tracing technology and RMS velocity). The experimental results show that two kinds of SAFT imaging have almost the same imaging performance, while the efficiency of RMS velocity SAFT imaging is almost 25 times greater than the SAFT based on Snell's law.

주제어

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제안 방법

In order to effectively calculate the propagation time of ultrasonic wave in multi-layer medium and ensure the resolution of SAFT imaging, the root mean square velocity model of seismic wave data processing is introduced to investigate a new SAFT imaging method in this paper [16]. The root mean square velocity model is used to calculate the approximate propagation time of the acoustic beam in multi-layer media, which is compared with the exact propagation time calculated by Snell's law to verify the effectiveness of the model.
The above method was used to analyze the remaining three defect holes, and the longitudinal and lateral sizes (s_g, s_l)of the defect holes under three imaging methods were counted respectively. The maximum voltage amplitude of the speckle noise and the defect hole shown in Fig.
The lateral dimension of defects was quantified by –6 dBdrop method, and the normalized intensity of sound pressure was analyzed.

대상 데이터

3, the target imaging area is 20 mm × 20 mm. The target imaging area is 15 mm away from the top surface of the test block and 22.5 mm away from the left side of the test block, and contains 4 edge through-holes with a diameter of 1.5 mm. A immersion probe with a center frequency of 5 MHz and a aperture of 12.

이론/모형

The root mean square velocity model is used to calculate the approximate propagation time of the acoustic beam in multi-layer media, which is compared with the exact propagation time calculated by Snell's law to verify the effectiveness of the model.

성능/효과

(2) The imaging resolution and SNR of the SAFT imaging based on the root mean square velocity model is consistent with which of the traditional SAFT imaging. Compared with B-scan imaging, the lateral resolution of the SAFT imaging based on the root mean square velocity model is improved by 23.
(3) The imaging efficiency of the SAFT based on the root mean square velocity model is improved almost 15 times than which of the traditional SAFT. It shows that the SAFT imaging based on the root mean square velocity model is an efficient SAFT imaging for immersion ultrasonic testing.
4 mm. It could be seen that the lateral resolution of the SAFT imaging based on the root mean square velocity model was consistent with which of the traditional SAFT imaging, and it is improved by 24% with respect to B-scan imaging.
35 mm. It could be seen that the longitudinal resolution of the SAFT imaging based on the root mean square velocity model was consistent with which of the traditional SAFT imaging, and the increase of longitudinal resolution is not obvious with respect to B-scan imaging.
Taking the immersion ultrasonic imaging of steel block as an example, the imaging efficiency and signal-to-noise ratio (SNR) of B-scan imaging, traditional SAFT imaging, SAFT imaging based on root-mean-square velocity model are compared. The amplitude of the echo signal along the center axis of the defect hole is analyzed, and the echo signal after DAS is enveloped and normalized, the imaging accuracy of the SAFT imaging based on the root mean square velocity model is verified.
3 dB higher than the imaging SNR of B-scan imaging. The results show that the root mean square velocity model can be used to the DAS calculation in SAFT imaging, which provides an efficient SAFT imaging for immersion ultrasonic testing.
The results show that when the half-power divergence angle is less than 7°, the error of propagation time in water-steel media with the thickness of 56 mm and 35 mm is less than 44 ns.

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