Real-Time 3-D Volumetric Ultrasonic Imaging of Multilayered Structures Using Phase Shift Migration-Based Depth Extrapolation.

Comprehensive 3-D volumetric characterization is a critical pursuit in nondestructive evaluation and advanced materials engineering. However, high-fidelity 3-D ultrasonic imaging has traditionally been constrained by the dual challenges of hardware scalability and computational efficiency. Although row-column addressed (RCA) arrays have been shown to substantially reduce the hardware complexity of volumetric data acquisition, the computational efficiency remains a critical bottleneck, particularly in stratified media, where accurate refraction correction typically requires extensive computations. This study developed an orthogonal phase shift migration (OPSM) method, specifically designed for RCA arrays. By formulating an exact vertical wavenumber expression in the frequency-wavenumber (f-k) domain, OPSM recursively extrapolates the acquired data to arbitrary depths. The imaging condition is then applied directly in the f-k space to generate the 3-D image. Experimental results demonstrate that OPSM maintains an average generalized contrast-to-noise ratio (gCNR) within 5.42% of conventional delay-and-sum (DAS) beamforming, while achieving a maximum computational speedup of 1800-fold. The 3- volumetric reconstruction is consistently completed in approximately 1 s on consumer-grade personal computers. These results indicate that OPSM provides a definitive solution for real-time volumetric imaging in multilayered structures, offering a high-speed, in situ 3-D characterization tool for industrial nondestructive evaluation.