An ultrasonic multi-wave focusing and imaging method for linear phased arrays*

Abstract

To overcome the inherent limits of traditional single wave imaging for nondestructive testing, the multi-wave focusing and imaging method is thoroughly studied. This method makes the compressional waves and shear waves focused in both emission and reception processes, which strengthens the focusing energy and improves the signal-to-noise ratio of received signals. A numerical model is developed to study the characteristics of a multi-wave focusing field. It is shown that the element width approaching 0.8 wavelengths of shear waves can keep a balance between the radiation energy of two waves, which can achieve a desirable multi-wave focusing performance. And an experiment using different imaging methods for a linear phased array is performed. It can be concluded that due to the combination of the propagation and reflection characteristics of two waves, the multi-wave focusing and imaging method can significantly improve the imaging distinguishability of defects and expand the available sweeping range to a sector of –65° to 65°.

Numerical analysis of the phased array imaging with a stacked plate buffer

“…The beam forming and focusing are possible by adjusting the delay given to the vibrating elements, and new technologies have also been developed, such as a full matrix capture (FMC), which collects a very large number of waveforms by switching the vibrating elements, and a total focusing method (TFM), which is the imaging algorithm using the large number of waveforms collected by the FMC. [14][15][16][17][18][19][20][21][22] However, when considering the installation of a phased array probe in plant piping to monitor crack propagation during operation, the high temperature resistance of the phased array probes becomes important when the piping is subjected to high temperatures. For example, in new nuclear power plants that use liquid sodium as a coolant, the temperature of the piping can reach several hundred degrees Celsius, while a typical phased array probe can only maintain its functionality up to about 60 °C.…”

Full-Matrix Imaging in Fourier Domain towards Ultrasonic Inspection with Wide-Angle Oblique Incidence for Welded Structures

“…With the growing need for nondestructive evaluation, phased array techniques have been developed to enable precise defect localization and characterization within the region of interest (ROI). Improving on those, the emerging total focusing method (TFM), utilizing full matrix capture (FMC) datasets, outperforms conventional phased array imaging in ROI resolution and sensitivity to small defects [13][14][15]. However, the focusing law of the TFM for oblique incidence is time-consuming, attributed to the intricate refractive path dictated by Snell's law.…”