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## Metamaterials Developed To Bend Sound Waves, Deflect Tsunamis110

Posted by samzenpus
from the building-it-better dept.
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.'"
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## Metamaterials Developed To Bend Sound Waves, Deflect Tsunamis

• #### Re:Tsunami "Bending" can't work (Score:5, Informative)

on Friday December 27, 2013 @02:59AM (#45794119)

You are talking about redirecting amounts of energy in a wall of water than may be 10-20 feet high or more, yet it comes in as a solid wave and the elevation stays at that height causing water to move inland extremely fast for a long time.

It would be easy to calculate what amount of energy that would be in a width of a town: E = .5 * mass x v^2. You are talking about amounts of energy that would dwarf anything a major multi-unit power plant could produce.

Some scientists working with this sort of approach seem to think there is some potential for handling seismic energy.

How to Repel an Earthquake [sciencemag.org]

"It's very cool stuff," says Ulf Leonhardt, a theoretical physicist at the University of St. Andrews in the United Kingdom who was not involved with the study. "It's a step toward manipulating seismic waves and done in a genius way." ...

The scientists created their jumbo-sized metamaterial in August 2012 by drilling holes in a thick bed of silt and clay near the city of Grenoble in the French Alps. The cylindrical holes stretched down about 5 meters into the earth, but were also skinny, only 32 centimeters wide. They were arranged in a rectangular grid of three rows of 10 holes each. The holes changed the density and stiffness of the earth and, thus, the speed and direction of vibrations rippling through the ground, forming a seismic metamaterial. The scientists then shook the earth on one side of the grid using a vibrating soil-compacting machine that they had placed underground. That machine created 50 seismic surface waves per second with a wavelength of 1.56 meters—about the same as the distance between the holes, though shorter than typical wavelengths from earthquakes.

Sensors placed throughout the site showed that the waves couldn't get past the grid of holes, bouncing off of it instead, the researchers report in a paper posted on the arXiv online preprint server. The waves just barely got by the second row of holes and couldn't even touch the third row, leaving the ground on the other side unshaken.

• #### Sound proofing... (Score:4, Informative)

on Friday December 27, 2013 @03:57AM (#45794279)

This is where the money in this idea lies. If you had an effective way to completely deaden low-end bass, then you'd dominate the market. Being able to build a whisper quiet nightclub or listening room would be incredible.

I'm about to embark on some deadening and sound proofing in my basement theatre, and I'm now thinking I really need to look into the metamaterial research to see if it can offer anything there.

• #### Re:Tsunami "Bending" can't work (Score:3, Informative)

on Friday December 27, 2013 @06:36AM (#45794743) Homepage
Yeah, but the solution to the problem in high energy physics is to make sure the high energy things don't touch anything important.

So, in this case, all we need to do is to levitate the ocean.

And you do realise that the mass of these pulses that LHC is trying to bend is only a tenth of a millionth of a gram? Tsunamis weigh quite a bit more than that.

But jesting aside, the article does look mostly bullshit, as it's highly inappropriate to model tsunamis as waves and solutions as working upon waves. They're so low frequency they're effectively DC. That's why in the term "tidal wave" is inappropriate - the "tidal" part is fine - in fact, it's almost perfect - it's the "wave" part that's misleading.

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