Abnormal Reflection of Airborne Sound Using Acoustic Metasurface with Subwavelength Apertures

The abnormal reflection caused by the subwavelength aperture and rigid wall is investigated theoretically. On the basis of analyzing the radiation impedances of the air columns at both ends of the aperture, it is found that the acoustic energy will be stored in transmitted region and released to incident region through the aperture, making the phase shifts of the reflected wave cover almost 2p span by adjusting the aperture transverse dimensions. A planar acoustic metasurface (AMS) constructed by an array of subwavelength apertures with different transverse dimensions and a rigid wall is demonstrated from both theoretical analysis and simulations. The results show that it has the ability to reflect acoustic waves into an unusual yet controllable direction. The total thickness of the designed AMS could be less than 1/10 of the incident wavelength, ensuring it being a good candidate for the miniaturization and integration of acoustic devices.