R. Colin Johnson

EE Times

(07/23/2009 11:24 AM EDT)

Just as submarines can be shielded from sonar, airplanes from radar and small areas from probing by laser beams, the very long wavelengths emanating from earthquakes can likewise be redirected around buildings, effectively making them "invisible" to seismic waves.

"Numerical simulations have been carried out for equations of thin plates. However, no experimental validation has been done thus far," said lead researcher Sebastien Guenneau. His team is currently working on a prototype to confirm their theory as well as scaling the approach for other applications.

"The next step in this research is first to experimentally validate the design of the cloak," said Guenneau.

Invisibility cloaks work by harnessing metamaterials--regular patterns of dielectrics that resonate at the cloaking frequency. The technique effectively diverts electromagnetic energy around objects. While the waves appear to be traveling in a straight line without interruption, metamaterials speed up the waves slightly as they are bent around the cloaked object. Hence, seismic waves emerge in-phase on the other side apparently unchanged.

Earthquakes emit body and surface waves. The U.K.-based researchers claim to have designed a cloak using giant-sized metamaterials that dampen the most destructive surface waves that are coupled to pressure and shear-body waves. Using large rings of a flexible metamaterials spaced around building foundations and tuned to the wavelength of the waves to be diverted, the researchers claimed the most destructive surface waves can be diverted around entire buildings.

The project is still in its design stage, with the researchers currently characterizing polymers and other metamaterials for giant ring resonators that could be tuned to a seismic wavelength. According to the group's computer simulations, seismic waves can be diverted with metamaterial rings made from multiple concentric layers separated with an isotropic elastic filler.

The current design uses 10 layers of six different materials that the researchers claim will be easy to manufacture for use in building foundations.

Experimental confirmation of the metamaterials is underway, and the researchers also are experimenting with methods for diverting shock waves around passengers during automobile accidents.

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