An acoustic metasurface made of a composite structure of cavity and membrane is proposed and numerically investigated. The\ntarget frequency is in the low frequency regime (570Hz). The unit cells, which provide precise local phase modulation, are\nrather thin with thickness in the order around 1/5 of the working wavelength. The numerical simulations show that the designed\nmetasurface can steer the reflected waves at will. By taking the advantage of this metasurface, an ultrathin planar acoustic axicon,\nacoustic lens, and acoustic nondiffracting Airy beam generator are realized. Our design method provides a new approach for the\nrevolution of future acoustic devices
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