Anomalous wavefront manipulation and broadband sound absorption by metasurfaces with periodic subwavelength modulation

Both periodic subwavelength structures and phase gradient metasurfaces have opened up new degrees of freedom to manipulate the acoustic waves respectively. In this study, a periodic subwavelength structure is introduced into the metasurface to modulate the acoustic surface waves deduced by the phase gradient. Anomalous sound reflection beam steering is observed, as well as significant sound absorption is achieved with deep subwavelength thickness in a broadband frequency range as damping is considered. We comprehensively analyze the joint effect of the phase gradient and subwavelength periodic constraints. A local multiple reflections mechanism is proposed to reveal the underlying physics and the acoustic performances, showing an excellent agreement. Our realization opens a new perspective for the study of acoustic metasurfaces and paves the way for the design of novel devices such as acoustic holograms and broadband acoustic absorbers with deep subwavelength thickness.