Nondestructive subwavelength metablocks for manipulation of shear horizontal waves

Metamaterial-aided ultrasonic nondestructive testing (NDT) has emerged as a promising field for overcoming limitations in conventional defect detection. However, the practical implementation encounters challenges because traditional metamaterial design typically requires breaking structural continuity, and the 2D/3D periodic distribution of metamaterials leads to a significant increase in complexity. This study presents an innovative metablock design strategy characterized by nondestructive properties, one-dimensional periodicity, and broadband performance (20 kHz bandwidth). Focusing on the fundamental shear horizontal (SH 0 ) wave, a preferred mode in NDT due to its nondispersive propagation characteristic, a subwavelength rectangular metablock capable of effective wave manipulation through antiresonance mechanisms is developed. The proposed metablock can be easily manufactured and attached to the host structure without compromising the structure’s integrity. A theoretical model is developed to describe the mechanism of wave isolation and simultaneously design the metablock’s dimensions. Practical demonstrations include one-dimensional isolators blocking full-angle incident SH 0 waves and waveguides guiding SH 0 wave propagation, which are validated by simulations and experiments. Furthermore, a metablock-aided inspection system is developed to demonstrate enhanced detection capabilities for oblique cracks (oriented between 0° and 90°), most of which fall outside the capability of conventional Pulse-echo ultrasonic testing. Simulation and experimental results confirm significant improvements of the proposed system in crack identification accuracy and extended inspection coverage with a wide frequency range, highlighting the metablock’s promising applications in SH 0 wave-based NDT.