Acoustic phase-gradient metamaterial design through detuned supermodes.

Over the past few decades, acoustic phase-gradient metamaterials have attracted considerable attention due to their extraordinary capability to manipulate wavefronts flexibly. Here, we propose a detuned-supermode approach for designing acoustic phase-gradient metamaterials. Unlike conventional strategies, our structure unit consists of two coupled parallel waveguides and supports the propagation of an odd-symmetric supermode. Leveraging the plane-wave-like characteristic of the supermode propagation, arbitrary phase shift and high transmission efficiency are achieved by adjusting the detuned propagation constant. To verify the feasibility and practical performance of the proposed approach, both anomalous refraction and self-accelerating propagation of acoustic waves are demonstrated through numerical simulations and experimental measurements. This work may pave a technical path for the manipulation of acoustic waves and the design of functional acoustic devices.