Big waves can be bad news for coastal areas, and over time, even moderate wave action can erode beaches down to nothing. In one of those schemes that sounds crazy but isn't, Chinese researchers have developed a system that uses concrete cylinders to render coastlines effectively invisible to incoming waves.
Physicists have been working on invisibility cloaks made out of metamaterials that are capable of messing with light waves to divert them away from or around whatever you want to make disappear. On a fundamental level, light waves and ocean waves are the same type of thing, and Chinese scientists have been able to extend this wave-altering concept to water.
Instead of using some kind of crazy metamaterial, the researchers just built arrays of concrete cylinders out in the water. The cylinders are hollow, with narrow slits in the sides. As waves travel past the cylinders, water enters through these slits, and after the wave passes, the water drains out again. The trick here is that if the cylinders are "tuned" properly (with the right size slits), water will flow in at the peak of each wave and then out at the trough, effectively canceling out up to 90% of the wave's intensity and protecting anything on the other side of the cylinders. And if you want, all that in-and-out action of water through the cylinders coul be used to drive an electric generator. New Scientist has this helpful diagram if you're having a bit of trouble picturing the system in action:
Most of the time, waves aren't all moving at the exact same frequency, but it should be possible to adapt the cylinders to respond to different frequencies at the same time, even up to tsunami sizes. Even if the cylinders aren't all resonating perfectly, they'll still be able to significantly reduce wave energy. Tabletop experiments have shown that this idea works on a fundamental level, and it may even be possible to adapt the current generation of wave power generation systems to work as coastal protectors at the same time.
Via New Scientist