Acoustic accelerating beam based on a curved metasurface

General relativity directly relates the curvature of spacetime to the energy and momentum whatever matter and radiation are present. In this letter, the different curved shapes of acoustic metasurfaces are used to mimic various curved spacetimes, while the different phase shift distributions are used to mimic different movements in the curved spacetime. Consequently, a new degree of freedom is attained by introducing the curved geometry of the metasurface, which is fully different from the straight geometrical structures in conventional acoustic metasurfaces. We have experimentally implemented multi-directional transmission by a curved metasurface. Furthermore, as the general relativity is constructed using tensors, it exhibits general covariance: its laws share the same form in all coordinate systems. With the general covariance, covariant structures can produce an identical acoustic field by the covariant transformation between different curved metasurfaces, such as Rindler-analogous transformation, which has been experimentally realized with different curved metasurfaces. This general covariant design method can be extended to many other sound manipulations. Published under license by AIP Publishing.