Ultrasonic Imaging Technique for NDE: Arbitrary Virtual Array Source Aperture with using Sign Coherence Factor

In this paper, we propose the ultrasound imaging method, arbitrary virtual array sources aperture (AVASA), using signal sign coherence (SC) information to inspect thick, highly attenuating structural components and enhance image resolution. The AVASA-SC employs phased array (PA) parallel transmission to focus beamforming at multiple virtual sources, improve the signal-to-noise ratio (SNR) of received A-scan signals, and record the reflected signals with all the array elements. The high-resolution imaging is reconstructed on the reception by an AVASA beamformer that virtually focuses on each point in the inspection region through the coherence summing of the signal sign bit, reducing image processing time. AVASA effectively images thicker structures by focusing the ultrasound beam at virtual sources through exciting parallel transmission. However, in AVASA, the SNR of deeper reflectors can be reduced due to signal amplitude-based image reconstruction. Therefore, AVASA-SC uses the instantaneous signal sign bit of the AVASA beamforming aperture data to create imaging. To compare AVASA-SC’s defect SNR and imaging resolution for deeper-located defects, two test samples (one with known defects, one with unknown) were scanned using AVASA and full matrix capture-total focusing method (FMC-TFM) techniques. AVASA-SC significantly improves image resolutions, enabling enhanced defect characterization.