3D ultrasonic imaging based on synthetic aperture focusing technique and space-dependent threshold for detecting submillimetre flaws in strongly scattering metallic materials. (December 2021)

• Record Type: Journal Article
• Authors: Qin, Liang; Zhang, Shuzeng; Song, Yongfeng; Li, Xiongbing
• Is Part Of: NDT & E international. Volume 124(2021)
• Publication Date: 2021-12
• Subjects: 3D image -- 3D SAFT -- Space-dependent threshold -- Noise statistic -- Submillimetre flaw; Nondestructive testing -- Periodicals; Contrôle non destructif -- Périodiques; Electronic journals; 620.1127
• DOI: 10.1016/j.ndteint.2021.102523
• Languages: English
• ISSNs: 0963-8695

Abstract

Abstract: When the traditional ultrasonic method is used to detect submillimetre flaws in strongly scattering metallic materials, missed detections or false positives may occur as flaw signals are usually submerged in the noise. In this work, a 3-dimensional (3D) imaging method is proposed to detect submillimetre flaws. The Synthetic Aperture Focusing Technique (SAFT) is introduced to improve the signal-to-noise ratio by reconstructing flaw signals, and the noise statistic method is used to determine a space-dependent threshold for distinguishing flaw signals and noise. The signals for flaws at different depths are enhanced by the 3D SAFT, and a 3D image is constructed using these anomalous signals to stereoscopically show internal flaws. Experiments are performed to detect flaws with diameters of 0.2 mm and 0.3 mm in a 304 stainless steel specimen and the results show that all these flaws can be found in the 3D image with high resolutions. Highlights: A 3D image is proposed to detect submillimetre flaws in strongly scattering material. 3D SAFT theory is introduced to improve the SNR of submillimetre flaws. A space-dependent threshold theory is developed using a noise statistical theory. The space-dependent threshold can be used to filter noise at different depths.