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.