An optimized laser ultrasonic synthetic aperture imaging method using differential technique

Abstract

Laser ultrasonic synthetic aperture focusing technique (SAFT) is susceptible to multiple modes of ultrasonic generated by laser pulse. In this work, we propose an optimized synthetic aperture imaging method based on the differential technique, resulting in the effective detection of internal defects. The laser ultrasonic SAFT finite element model is established, and the models are calculated in the case of existing internal defect or not. Thereby, the original ultrasonic data containing the defect reflected waves and the differential data are obtained, and the internal defects are reconstructed by the delay superposition algorithm. The results show that the defect imaging is submerged in the high-amplitude background noise superimposed by the surface acoustic wave; when only the original data are used. However, the optimized SAFT imaging based on the differential technique can not only reduce the interference of other mode waves on the imaging area significantly, but also retain the defect reflected waves effectively. Moreover, the imaging and precise locating of multiple defects are realized, which pave the way for enhancing the internal defects detection ability of laser ultrasonic.

Research on Photoacoustic Synthetic Aperture Focusing Technology Imaging Method of Internal Defects in Cylindrical Components

“…Ultrasonic C-scanning uses the probe to scan along the surface of the sample, and can obtain images of the sample in the cross-section at a selected depth, but the size of the defect itself is difficult to determine [ 21 ]. Synthetic aperture focusing technology (SAFT) uses small aperture arrays to dynamically synthesize equivalent virtual large apertures, which can achieve high imaging resolution with small aperture arrays, and is especially suitable for high-resolution automatic detection of cylindrical components [ 22 , 23 , 24 ]. Dai [ 25 ] proposed an accurate frequency-domain synthetic aperture focusing technology based on 2D equivalent velocity mapping to detect and image internal defects in specimens.…”