The cloaking of sound and elastic waves could prove easier than cloaking light and have even more dramatic impacts. The seismic waves caused by earthquakes typically have wavelengths on the order of kilometers, so a cloak could be built from relatively large components and could channel the destruction around buildings, or even entire cities. Completely soundproof rooms could be possible by deflecting sound waves around the walls of the room.
The possibilities of this new technology continue to excite the engineering community. Until Vesalago's research, scientists had erred through their overly restricted interpretation of Snell’s Law. Vesalago’s revolutionary realization that physics does not deny the possibility of negative indices of refraction has allowed scientists to break through old boundaries and explore new perspectives. Young and enthusiastic minds at universities all over the country are finally working to make invisibility possible.
In order to make something invisible to the naked eye, all wavelengths of visible light must be refracted around the object simultaneously. The visible spectrum ranges from 400-790 THz, as can be seen again in Fig. 4. As of now, metamaterials only work for a specific wavelength of light, and designing the materials to defer the entire spectrum of frequencies will require new insights.
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