Transformation seismology tested in France.
Vulnerable buildings could someday be shielded from damaging earthquakes by surrounding them with "seismic invisibility cloaks". An early prototype of such a cloak has been tested experimentally by researchers in France. In principle, the concept could be extended to create protective barriers that divert earthquake energy away from sensitive facilities such as nuclear power plants.
Traditional earthquake engineering is based on damping and dissipating the energy absorbed by a building when it is hit by shock waves. Now, computational physicistSebastien Guenneau and colleagues at the Institut Fresnel and the geoengineering company Ménard have taken a different approach that involves modifying the ground around a building to divert seismic waves, effectively cloaking the structure from an earthquake's destructive energy. They have also conducted preliminary field tests on the efficacy of the design for earthquake protection.
Their design is the latest extension of the concept of metamaterials, which were first suggested for electromagnetic waves in 1968 by Soviet physicist Victor Veselago. The first metamaterials were built in 2006 by a team that included John Pendry at Imperial College London andDavid Smith at Duke University in North Carolina. Pendry, Smith and colleagues created artificial materials with negative indices of refraction – properties that do not normally occur in natural materials. Pendry and others also developed a mathematical tool called transformation optics to describe how a metamaterial should be structured to have the desired properties.
Pendry describes the research as "a completely new approach", although he points out that the cloak would require similar space to the region being cloaked. "It's not something you're going to do in Manhattan," he says. "On the other hand, it might be something you'd want to do if you had a very high-value strategic object such as a nuclear reactor." Cloaking expert Andrea Alú also says the work is "neat", but he sees a potential pitfall with the simple shield demonstrated here. "Whatever you don't transmit, you reflect," he says, "If you are in a crowded environment, you may cause problems for other buildings."
The researchers openly acknowledge this limitation. They are currently building the full cloak, which should control the flow of waves, ensuring they do not damage neighbouring structures. Gunneau concludes the involvement of the Ménard civil-engineering company shows the research "is likely to have real applications". "It's not just for fun," he says.