Researchers at the University of Hong Kong have discovered a new type of sound wave. The results of the experiment showed that sound in air or in liquids can be in the form of a transverse wave.

Scientists have developed a special micropolar plate that looks like a complex network of resonators. Inside the network, they are connected to each other, between them there is air that vibrates and supports sound. Dr. Wang, author of the study, explained that the lack of shear force in air or liquids is the reason that sound is a longitudinal wave.

Then he came to the conclusion that the shear force occurs when air is divided into “meta-atoms”. That is, to enclose the bulk air in small resonators with a size much smaller than the wavelength. The collective movement of these airy “meta-atoms” results in transverse sound on a macroscopic scale.

Using this method, scientists have demonstrated for the first time two types of interactions between air and sound. One of these results in negative refraction of transverse sound when it bends in opposite directions. Another generates sound vortices when transverse sound is excited.

In the theory of physics, there are two types of waves. In shear waves, such as light, vibrations are perpendicular to the direction of propagation of the wave. In longitudinal waves such as sound, they are parallel. But the latest discovery by Hong Kong scientists is changing this understanding of sound waves.

The results obtained pave the way for the development of new applications in the field of acoustic communication and acoustic sensing.