&ball; Physics 15, s.65
A water wave incident on a grooved wall is analogous to electromagnetic waves called surface plasmon polaritons.
The ability of metamaterials to direct light has enabled amazing inventions ranging from super-resolution microscopes to “invisibility” cloaks. But the physics behind these structures also applies to other waves, such as acoustic, seismic and water waves. Huanyang Chen and colleagues at Xiamen University in China have demonstrated a structure that can alter the propagation of surface water waves, creating a localized wave analogous to electromagnetic excitation called a surface plasmon polariton. .
Surface plasmon polaritons occur at the interface between a dielectric and a material with negative permittivity such as a metal. Generating equivalent excitation in surface water waves requires a similar type of interface, such as that between water and a vertical barrier. In this case, the parameter of water that is analogous to the permittivity of a metal is its depth. Of course, it’s impossible for water to have negative depth, but using metamaterials, Chen and his colleagues engineered the wave boundary conditions to achieve the same effect.
The team printed a patterned 3D plastic barrier with fine vertical grooves. They placed the barrier in a tub of water and, using a submerged screw propeller, produced waves that crashed against the grooves. After striking the grooved surface, the waves propagated parallel to the barrier as a series of localized surface plasmon-polariton type excitations. These excitations moved in a single direction along the barrier, going either left or right depending on the direction of rotation of the propeller.
Chen is interested in exploring the use of metamaterials to effectively alter other parameters, such as gravity, that control the behavior of water waves and in fabricating materials with a negative refractive index. He thinks such research could inspire new methods of water management.
Katie McCormick is a freelance science writer based in Seattle, Washington.
- L.Han et al.“Let’s polarize water waves,” Phys. Rev. Lett. 128204501 (2022).