Reflected wavefront manipulation by acoustic metasurfaces with anisotropic local resonant units

In this work, we develop a new gradient acoustic metasurface to manipulate reflective wavefronts arbitrarily. Each unit of the gradient metasurface is constructed of a locally anisotropic resonant structure, comprising a steel cylinder with an elliptical rubber coating embedded in epoxy. Phase shifts of the reflected wave over the full $2\pi$ range provided by different units can be realized by selecting the radius of the steel cylinder. With an appropriate design of the phase profiles along the acoustic metasurface, we can achieve anomalous reflection, a planar acoustic lens, and an acoustic cloak. The locally anisotropic resonant units have significant potential for engineering and manipulating acoustic wavefronts