In this paper, a tunable arc-shaped acoustic metasurface (AAM) carpet cloak has been proposed and systematically investigated. The AAM carpet cloak consists of covers, rotors, bolts and nuts. The rotors can be rotated continuously within the covers to form a reconfigurable hook channel mechanism. By setting various rotational angles, we construct two-dimensional (2D) tunable AAM carpet cloaks to achieve excellent stealth performances under different operating conditions. Numerical simulations and experimental results for the 2D carpet cloaks show good agreements. Furthermore, simulated results for three-dimensional (3D) carpet cloaks have demonstrated that tapered objects are successfully escaping from being detected. The tunable hook channel mechanism can be flexibly applied to arbitrarily curved metasurface carpet cloaks, making them closer to practical invisibility acoustic devices.

Self-accelerating beams have applications in optic and acoustic fields due to their peculiar properties. As a promising artificial two-dimensional metamaterial, a metasurface can be used as the generator of self-accelerating beams. However, restricted by the generalized Snell's law, most research hotspots focus on flat metasurfaces. In this Letter, the generalized Snell's law on an arbitrary curved reflective surface is discussed. Then, the phase profile for the self-accelerating beams generated from the curved reflective surface is derived based on the caustic theory. The metasurface consisting of the tunable spiral path units is constructed, and numerical and experimental validations are performed. The methodology developed in the present letter extends the applications of the self-accelerating beams.

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In this paper, the viscoelastic effect on the topologically protected interface states in two-dimensional (2D) solid phononic crystals (PnCs) is investigated. The valley topological interface states for the 2D in-plane and out-of-plane modes are generated on the interfaces between two PnCs with opposite topological phases. The complex band structures are calculated by the ω-k approach based on the weak formulation of the governing equations of wave motion, which is solved numerically by the finite element method. From the complex band structures, it is demonstrated that even though the material viscoelasticity is introduced into the systems, the topological interface states still exist. However, for the viscoelastic case, the topological interface states becomes the complex wave modes, which means that the interface states inevitably attenuate as they propagate in the viscoelastic PnCs. The amplitude of the elastic waves traveling along the interfaces exhibits an exponential decay, which can be analytically predicted based on the imaginary part of the wave number. Despite suffering from the attenuation due to the material loss, the topological interface states in the viscoelastic PnC structures also exhibit their robustness against the sharp bends or local disorders. In practice, the material loss is ubiquitous, and hence these results are relevant to the PnC devices based on the topological states.