Spoof surface plasmon polaritons (SSPPs) were first developed in electromagnetics and later extended to acoustics, enabling deep-subwavelength confinement and efficient surface wave transport. Currently, unidirectional SSPP excitation is typically achieved by tailoring the excitation sources, such as with vortex waves carrying orbital angular momentum beams or by employing gradient metamaterials, though both approaches often face limitations in tunability, efficiency, and implementation complexity. Here, we propose and experimentally demonstrate a high-efficiency and tunable mechanism for directional SSPP excitation, achieved through structural symmetry breaking. Specifically, by introducing a rotational degree of freedom that breaks the intrinsic symmetry of the combined triangular elements and grating structures, distinct SSPP coupling efficiencies are induced on both sides under normal incidence, enabling directional excitation. Numerical and experimental results verify the stable, unidirectional propagation enabled by this approach. Compared with existing methods, our design offers superior efficiency, tunability, and simplicity, providing a robust and adaptable solution for directional acoustic energy transport and subwavelength device designs.

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• Acoustic wave phenomena
• Surface plasmon polariton
• Diodes
• Waveguides
• Surface acoustic wave