Enhancing spatial resolution in sparse array ultrasound imaging using nonlinear beamforming: Simulation and experimental validation

Abstract

Sparse array ultrasound imaging offers a cost-effective and scalable solution for nondestructive testing (NDT). However, the reduced number of transceiver elements typically compromises resolution and contrast. To address this limitation, this study proposes a novel nonlinear apodization method, null subtraction imaging (NSI), integrated with the total focusing method (TFMNSI). This approach effectively suppresses side lobe and grating lobe artifacts, thereby improving lateral resolution and contrast without increasing computational complexity. Numerical simulations and experimental studies on steel samples show that TFM-NSI achieves a 36-96 % improvement in lateral resolution and a 71% reduction in artifacts. Notably, TFM-NSI with an 8element array achieves image quality comparable to conventional TFM with 64 elements, highlighting its superiority in array utilization. Further experiments on reinforced concrete (RC) slab confirm the potential of TFM-NSI for concrete NDT, enabling accurate measurements of rebar size and embedded defects. These results demonstrate TFM-NSI as a promising tool for advanced NDT applications in various engineering domains.