Inverse design of a metasurface-enhanced stacked plate buffer for ultrasonic phased array imaging

Abstract

Conventional stacked-plate buffers (SPBs) generate trailing-echoes that can obscure defect responses in ultrasonic phased-array imaging. This study proposes a metasurface-enhanced stacked-plate buffer (MESPB) and a hardware–software framework for reducing these effects without increasing the buffer dimensions. A semi-empirical sinusoidal boundary was optimized through simulation-in-the-loop inverse design using a mutation-enhanced basketball team optimization algorithm. Two- and three-dimensional simulations show that the optimized boundary redistributes the phase and propagation direction of S0-wave energy, thereby weakening coherent trailing echoes rather than promoting significant S0-to-A0 mode conversion. A phase circular statistical vector weighting strategy, combined with dispersion and time-gain compensation, was further incorporated into total focusing method imaging. Room-temperature experiments on side-drilled holes showed that, relative to the conventional SPB, the MESPB increased the mean signal-to-noise ratio and contrast-to-noise ratio by 9.14 and 5.15 dB, respectively, while providing an additional 17.51 dB improvement in artifact reduction ratio. Period-extended tests exhibited similar artifact-suppression trends. These results demonstrate substantial reductions in trailing-echo artifacts and improved defect detectability under the investigated conditions. Further validation under varied materials, defects, temperatures, fabrication tolerances, and long-term monitoring conditions is required before engineering deployment.