Short looping clip of a red toy boat bobbing on waves in the centre of the 86cm prototype of the wave concentrator device

A toy boat bobs inside a structure designed to raise the height of water waves in its centre. Credit: C. Li et al. Phys. Rev. Lett. 121, 104501 (2018)/APS

Fluid dynamics

Water waves grow tall with help from a trick of light

Ring-shaped invention channels waves to triple their height — a potential boon to wave energy.

A ring-shaped device can concentrate waves in water into a relatively small space without reflecting them — a technique that could make harvesting wave energy more efficient.

Structures that boost the height of water waves in a confined area can increase energy harvest from the sea. But these structures often end up reflecting waves, which dissipates some of their energy.

Inspired by their previous work using optical devices to control light waves, Huanyang Chen at Xiamen University in China, Zhenyu Wang at Zhejiang University in Hangzhou, China, and their colleagues created a ring of thin metal sheets, arranged like slides in a projector’s carousel. The structure channelled incoming waves towards the ring’s centre. By tailoring the length and depth of the gaps between sheets, the team created cavities that also caused reflected waves of a set frequency to interfere and cancel each other out, preventing reflections.

Tests in a tank showed that a prototype device that is 86 centimetres across could triple the height of waves at the ring’s centre, while leaving waves outside the ring undisturbed.