By ringing an object with a certain elastic material, it can be made invisible to mechanical waves, says the author of a new study. The principle is proposed to be extended to ground structures
William J. Parnell of the University of Manchester has developed a new theory of the "cloak of invisibility" working in the field of elastic vibrations.
In his article in Proceedings of the Royal Society A, the Briton showed how you can make waves smoothly bend around an object protected with Neo-Hookean solid materials.
Three cases of elastic wave passage in Parnell's computer model. The white circle is the source. The black circle is the protected cavity. In the first version, it is simply too small (compared to the wavelength) to create a noticeable distortion in the picture.
Such compositions have a non-linear relationship between mechanical stress and deformation. Parnell found that if a preliminary mechanical stress is created in an elastomer ring, then using a similar system, one can arbitrarily control the propagation of elastic waves of a certain type.
As a result, it is possible to achieve the effect when powerful mechanical vibrations of the medium (say, the ground) will pass through the protected object almost without distortion, as if it does not exist.
The technology is called "Elastodynamic Cloaking". Its general idea is similar to that put forward by another group of European researchers in 2009.
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However, there is a significant difference. In previous work, scientists proposed creating multilayer rings of metamaterial in the ground around buildings.
By combining polymers with different elastic properties, it is possible to achieve the construction of an object, the mechanical characteristics of which, that is, the reaction to the passage of a seismic wave, will radically differ from the characteristics of each component separately. (And this approach, by the way, is very similar to research in the field of "invisibility cloaks" working with electromagnetic waves.)
But William believes that inhomogeneous (and at the same time complex) metamaterials are not needed in this case. True, its scheme still needs to be improved. But in the long term, Parnell's work may lead to a new method of protecting buildings from earthquakes.
"If the theory can be expanded to larger objects, it will lead to the creation of 'cloaks' to protect structures. Or, perhaps more realistically, to protect the most important parts of these structures," - says the inventor.