First Test of Seismic Invisibility Cloak
The ability to steer electromagnetic waves around regions of space has revolutionised optics and sparked a global interest in Harry Potter-style invisibility cloaks. But it isn’t only photons that are the target of these devices.
Various engineers and physicists have also begun work on acoustic versions that steer sound. In particular, a few groups have begun to think about how this technology might be used to steer seismic waves round buildings. The idea would be to protect high value buildings such as nuclear power stations or airports. We examined just such a proposal last year.
So far, all these ideas have been numerical studies. Today, a group from the Institut Fresnel in Marseille and the ground improvement specialist company, Menard, both in France, say they’ve built and tested a seismic invisibility cloak in an alluvial basin in southern France. That’s the first time such a device has been constructed.
The secret of invisibility cloaks lies in engineering a material on a scale smaller than the wavelength of the waves it needs to manipulate. The appropriate sub-wavelength structures can then be arranged in a way that steers waves.