Phys.org December 7, 2021
According to the researchers in Hong Kong the absence of shear force in the air, or fluids, makes sound waves longitudinal. Synthetic shear force may arise if the air is discretized into “meta-atoms,” whose collective motion can give rise to a transverse sound on the macroscopic scale. To implement this idea they designed micropolar metamaterial like a complex network of resonators. Air was confined inside the mutually connected resonators, forming the meta-atoms. Through theoretical calculations they showed that the collective motion of meta-atoms produces the shear force, which gives rise to the transverse sound with spin-orbit interactions inside this metamaterial. They verified the theory by experiments. Using the metamaterial, they demonstrated two types of spin-orbit interactions of sound – the momentum-space spin-orbit interaction where sound bends in the opposite directions when passing through an interface and the other is the real-space spin-orbit interaction, which generates sound vortices under the excitation of the transverse sound. The findings provide new perspectives and functionalities for sound manipulations beyond the conventional scalar degree of freedom, and by manipulating the extra vector properties, scientists may be able to encode more data into the transverse sound…read more. Open Access TECHNICAL ARTICLE
Band properties of the 1D acoustic lattices. Credit: Nature Communications volume 12, Article number: 6125 (2021)Â