  We propose a nonlinear acoustic metasurface concept by exploiting the
nonlinearity of the locally resonant unit cells formed by curved beams. The
analytical model is established to explore the nonlinear phenomenon,
specifically the second-harmonic generation (SHG) of the acoustic waveguide and
validated through numerical and experimental studies. Novel nonlinear acoustic
metasurfaces are developed to demultiplex different frequency components and
achieve anomalous wavefront control of SHG in the transmitted region. To this
end, we demonstrate wave steering, wave focusing, and self-bending propagation.
Our results show that the proposed nonlinear metasurface provides an effective
and efficient platform to achieve significant SHG, and separate different
harmonic components for wavefront control of individual harmonics. Overall,
this study offers new avenues to harness nonlinear effects for acoustic
wavefront tailoring and develops new potential toward advanced technologies to
manipulate acoustic waves.
