'Earthquake cloaks' may one day make buildings invisible to devastating tremors

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London, June 27 (ANI): Let alone hiding persons or objects from prying eyes, future invisibility cloaks may even conceal buildings from the devastating effects of earthquakes, if physicists in France and the UK are to be believed.

Stefan Enoch of the Fresnel Institute in Marseille, France, is the researcher behind the "earthquake cloak" idea.

A research team led by Enoch has for the first time suggested that the physics of invisibility cloaks may one day enable scientists to design a cloak that could render objects "invisible" to destructive storm waves or tsunamis.

The seismic waves of an earthquake fall into two main groups: body waves that propagate through the Earth, and surface waves that travel only across the surface.

While controlling body waves will be too complex, Enoch's team say that controlling surface waves is within the ability of conventional engineering.

Team member Sebastien Guenneau, associated with the UK-based University of Liverpool, says that the finding attains significance as it is surface waves that are more destructive.

The researchers have revealed that the new theoretical cloak comprises a number of large, concentric rings made of plastic fixed to the Earth's surface.

They say that the stiffness and elasticity of the rings must be precisely controlled to ensure that any surface waves pass smoothly into the material, rather than reflecting or scattering at the material's surface.

According to them, while travelling through the cloak, waves are compressed into tiny fluctuations in pressure and density that travel along the fastest path available.

The researchers believe that by tuning the cloak's properties, that path can be made to be an arc that directs surface waves away from an area inside the cloak. When the waves exit the cloak, they return to their previous, larger size.

Unlike some of the optical invisibility cloaks studied in recent years, the new cloak is "broadband" and thus can divert waves across a range of frequencies.

The research group say that this becomes possibly by tuning different rings of the cloak to incoming waves of different frequencies. Waves pass largely unaffected through rings not tuned to their frequency.

"The outer rings remain nearly still, but the pair of rings tuned to the frequency of the wave move like crazy, bending up and down and twisting. For each small frequency range, there's one pair of rings that does most of the work," New Scientist magazine quoted Guenneau as saying.

Thus far, the researchers have simulated cloaks containing as many as 100 rings, even though fewer would be needed to protect against the most common kinds of earthquake surface waves.

As to how this technique can be applied to buildings, Guenneau says that they may be built into the foundations.

Even though work remains to be done to replicate the theoretical results experimentally, physicist Ulf Leonhardt at the University of St Andrews, UK, thinks that it is possible that invisibility physics may see its first real world applications of in guiding seismic or ocean waves rather than to manipulate light.

"I think this is fantastic - I really like taking ideas that have emerged from optics and using them in other applications," he said.

A research article describing the "earthquake cloak" idea has been published in the journal Physical Review Letters. (ANI)

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