Metamaterials Developed To Bend Sound Waves, Deflect Tsunamis 110
cold fjord writes in with this story about some new possible applications for metamaterials. "A new way of assembling things, called metamaterials, may in the not too distant future help to protect a building from earthquakes by bending seismic waves around it. Similarly, tsunami waves could be bent around towns, and sound waves bent around a room to make it soundproof. ... Metamaterials are simply materials that exhibit properties not found in nature, such as the way they absorb or reflect light. The key is in how they're made. By assembling the material — from photonic crystals to wire and foam — at a scale smaller than the length of the wave you're seeking to manipulate, the wave can, in theory, be bent to will. ... Ong and others say ... they could be used to redirect other kinds of waves, including mechanical waves such as sound and ocean waves. French researchers earlier this year, for example, diverted seismic waves around specially placed holes in the ground, reflecting the waves backward. Ong points to the possibility of using what has been learned in reconfiguring the geometry of materials to divert tsunamis from strategic buildings.'"
Deflector shields (Score:4, Interesting)
I don't think anyone ever expected that something akin to actual deflector shields for use on earth might be practical anytime soon, that they would always be the stuff of science fiction. At least this offers the possibility of actually making something like them with matter and not a theoretical energy shield requiring massive nuclear reactors.
Very interesting stuff - Metamaterials [popsci.com]
So put it under a freeway! (Score:4, Interesting)
Each hole might be of manageable size. But the array would be on the order of the same size as the town. That's a lot of holes and a lot of property you are going to be perforating.
It must be on the scale of the town IN ONE DIMENSION. Linear-square law: The bigger the area you're protecting, the lower the percentage of the area you need to perforate.
So you need to perforate a strip around the town to do this? Do it while you're ALREADY perforating such a strip. Like when you're building (or revamping) the next beltway-freeway around the city of interest, or approving a rezoning for the construction of a new outer subdivision.
Re:Tsunami "Bending" happens (Score:2, Interesting)
You are confusing the length of the wave front with the wavelength. Try swinging what you've got in your head around ninety degrees to cut through the wave cross section and you'll see that the scale is far more manageable.
Am I? I don't see how that is... and I'm a tsunami researcher! Literally, I've spent years of my life running (and developing the models for) tsunami simulations.
Earthquakes typically happen on scales of O(100km), so the initial waves produced, often at depths around 4km, have a wavelength of O(100km). In shallower water, say 100m, the wavelength is then O(10km), as the wavelength goes with the square root of the depth. There are other tsunami sources too, but we'll just stick to an order of magnitude estimate.
Now you see how metamaterials, which are structures with many sub-wavelength elements gathered in a way to produce interesting macroscopic behavior, would be difficult to use for tsunamis. You want to create structures in the ocean that are maybe O(10km) into the ocean, and then probably also O(10km), maybe more, along the shoreline to protect a city? And you'll need them to be substantial in the vertical, as well, since this isn't like laying down a tarp.
The comment in TFA about deflecting tsunamis was just an offhand thing, by someone who specializes in a completely different thing... I wouldn't put any weight in it. Even if you found a way for something to actually work, and somehow have a price tag that is not astronomical (you have any idea how much it costs to move even "dirt" around offshore?), I can't imagine anyone building it -- the seafloor is remarkably well utilized off most big cities, between cables being run out, channels for shipping, fishermen needing certain places undisturbed, offshore dumping locations, etc.