Non-destructive laser-ultrasonic Synthetic Aperture Focusing Technique (SAFT) for 3D visualization of defects

One of the challenging problems in non-destructive evaluation is related to identification and sizing of flaws. A high resolution image of the scanned part is required. This allows, through using adequate post-processing of data, to perform localisation and sizing of a flaw. Several techniques have been introduced recently for this purpose. These include among others the synthetic aperture focusing technique, inverse wave-field extrapolation and the total focusing method. However, large uncertainties are affecting the inverse problem solution as provided by these methods when dealing with small defects. It was recognized that reconstruction based on the ultrasonic synthetic aperture focusing technique elaborated in frequency domain provides high resolution imaging even at large distances. This work focused on this promising procedure for the special case of ultrasonic imaging of flaws in 2D elastic medium under plane strain conditions, where the image is provided by a B-scan. Robustness of detection was investigated through perturbing the radargram by white noise and assessed as function of noise energy. It was found that synthetic aperture focusing technique is insensitive to noise.

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Laser-induced ultrasonic measurements for the detection and reconstruction of surface defects

Acta Acustica ◽

10.1051/aacus/2021031 ◽

2021 ◽

Vol 5 ◽

pp. 38

Author(s):

Feiming Qian ◽

Guangzhen Xing ◽

Ping Yang ◽

Pengcheng Hu ◽

Limin Zou ◽

...

Keyword(s):

Surface Defects ◽

Signal To Noise Ratio ◽

Ultrasonic Measurement ◽

Laser Beams ◽

Synthetic Aperture ◽

Correct Identification ◽

Synthetic Aperture Focusing ◽

Sequential Generation ◽

Synthetic Aperture Focusing Technique ◽

Non Destructive

Laser-induced ultrasonic measurement is a non-contact non-destructive technology that can be employed for the testing and assessment of surface defects. In order to improve the correct identification of defects, the full matrix capture (FMC) and total focusing method (TFM) are applied on the imaging process. FMC data includes A-scans resulting from the combination of all measurement axes defined by the sequential generation and detection of utilized laser beams in the system. In this paper, an aluminium block with four holes whose diameters range from 1 mm to 2.5 mm is assessed through B-scans, the synthetic aperture focusing technique (SAFT) and FMC/TFM. The results demonstrate that the FMC/TFM technology can significantly improve the imaging quality and signal-to-noise ratio (SNR). In addition, this method has higher lateral resolution and larger imaging range compared with traditional B-scans.

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ULTRASONIC IMAGING SYSTEM USING A 2D ENVELOPE BEAMFORMING TECHNIQUE: IN-HOMOGENEITIES LOCATION

Journal of Computational Acoustics ◽

10.1142/s0218396x04002419 ◽

2004 ◽

Vol 12 (04) ◽

pp. 571-585

Author(s):

L. MEDINA ◽

E. MORENO

Keyword(s):

Imaging System ◽

Side Lobe ◽

Ultrasonic Pulse ◽

Image Resolution ◽

Synthetic Aperture ◽

Water Tank ◽

Synthetic Aperture Focusing ◽

Longitudinal Resolution ◽

Synthetic Aperture Focusing Technique ◽

Beamforming Technique

An algorithm has been developed to implement synthetic aperture focusing technique for B-scan. This is made at a several transmitter/receiver locations to form a map of ultrasonic reflectivity on the insonified region, considering the path travelled by the ultrasonic pulse from the transducer to the target and back again. To reconstruct the image, a time domain beam-former is applied to the envelope of the detected signals. This method minimizes the side-lobe amplitude and the restriction of λ/2 distance between two adjacent transducer positions can be neglected without loosing image resolution. The present work is focused on the location of the in-homogeneities, caused by the presence of a phantom immersed in a water tank. The results are presented when the distance between two adjacent transducer positions are varied from 0.5λ to 2.5λ showing that the longitudinal resolution is not affected but the lateral resolution becomes poorer when the distance is about 2λ. The error in the longitudinal location of in-homogeneities is within the minimum detectable distance of the system, while the lateral location error is increased when the distance between any two adjacent transducer positions is larger than 1.5λ.

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