Frequency-Selective Transmission Control of Ultrasonic Guided Waves in T-Shaped Pipes Using Acoustic Metamaterials: Computer Modeling and Experimental Validation

Structural health monitoring (SHM) of ship piping systems is a core component of predictive maintenance strategies for complex marine engineering systems. During the detection of ship T-shaped pipes using ultrasonic guided waves, signal overlap arises from the diffusion of guided wave branches. To address this issue, an intelligent wave-guidance mechanism based on acoustic metamaterials is proposed for dynamic propagation control of ultrasonic guided waves. First, a metamaterial unit composed of a stainless steel substrate and a copper column is designed. The control of bandgap characteristics by lattice constant, column diameter, and column height is systematically investigated, and a design range of structural parameters with optimal bandgap is obtained. The particle swarm optimization algorithm is used to design and optimize two metamaterials, Acoustic-metamaterials-1 (AMs-1) and Acoustic-metamaterials-2 (AMs-2), which further improve the bandgap performance and achieve a transmission loss of over 30 dB for guided waves at 100 and 150 kHz, respectively. Simulation and experimental verification show that when AMs-1 and AMs-2 are deployed in the left and right branches of the T-shaped pipe, respectively, wave propagation can be achieved according to the excitation frequency. At 100 kHz excitation, the guided wave preferentially propagates along the right branch, while at 150 kHz excitation, it preferentially propagates along the left branch. This method actively regulates the guided wave propagation trajectory at the structural level, thereby preventing signal overlap at the T-shaped pipe and offering a novel technical solution for the efficient damage detection and predictive maintenance in ship pipe systems.