NBF - Fudan University in Shanghai, China, have come up with a way to create shield against water waves that, unlike Enoch and Guenneau's set-up, could also double up as a wave-energy plant. Hu's team proposes using a rectangular array of stationary cylinders fixed to the sea floor in coastal waters. "The resonating cylinder array that we studied can be seen as a type of metamaterial for water waves," Hu claims.
Each hollow cylinder would be split vertically into quarter-circle arcs that fill up with water, and discharge it, depending on the water level surrounding them (see diagram). Although the cylinders are completely still, this constant filling and discharging is a form of oscillation and so is analogous to the electromagnetic oscillators that interfere with light waves in an invisibility cloak. By adjusting the width of the vertical slits, the size of the cylinders, and their spacing, Hu calculates that the array could be tuned to water waves of a particular frequency so that it drains the peaks and then discharges to fill in the wave troughs - in effect dismantling those waves. Using several arrays with different spacing and various sizes of cylinder, it might even be possible to block waves of several different frequencies - and perhaps even tsunamis, Hu claims. The result should be a huge reduction in waves within the array, and as a result, protection for any coastline or shore behind it, he says.Physical Review Letters - Negative effective gravity in water waves by periodic resonator arrays