Physicists have discovered a special transverse sound wave

The research team has discovered a new type of sound wave: an airborne sound wave vibrates transversely, carrying both rotation and orbital angular momentum like light. The findings changed scientists' previous beliefs about sound waves and opened the way for the development of new applications in acoustic communication, acoustic sensing, and imaging.

Can you imagine that sound travels in the same way as light? A research team at the City University of Hong Kong (CityU) has discovered a new type of sound wave. Physics textbooks tell us that there are two kinds of waves. In transverse waves, such as light, the vibrations are perpendicular to the direction of wave propagation. In longitudinal waves, such as sound, the vibrations are parallel to the direction of wave propagation. However, the latest discovery by CityU scientists changes this understanding of sound waves.

Concept and realization of "micropolar metamaterial"

To realize this idea, he ingeniously designed a type of artificial material called "micropolar metamaterial" that appears as a complex network of resonators. Air is enclosed inside these interconnected resonators, which form "meta-atoms". The metamaterial is hard enough to vibrate. Theoretical calculations have shown that the collective motion of these air "meta-atoms" actually creates a shear force that causes transverse sound with spin-orbit interactions inside this metamaterial.

In addition, the research team found that the air inside the micropolar metamaterial behaves like an elastic material, thus supporting transverse sound with both rotational and orbital angular momentum.

Research has shown that air-borne sound or sound in fluids can be a transverse wave and carry full vector properties such as angular momentum just like light. It provides new perspectives and functions for sound manipulation beyond conventional scalar degrees of freedom.

By manipulating these extra vector properties, in the future, scientists may be able to encode more data into transverse sound to break the barrier of traditional acoustic communication with normal sound waves.

The discovery may pave the way for the development of new applications in acoustic communication, acoustic sensing, and imaging.

Full article: https://www.sciencedaily.com/releases/2021/12/211207152541.htm