Negative refraction in water

The possibility of negatively refracted light—for which both the permittivity and permeability are negative—was postulated in 1967 and experimentally realized in 2000. (For more, see the article by John Pendry and David Smith in Physics Today, June 2004, page 37 .) The phenomenon has been exploited to create convergent flat lenses, usually made of so-called metamaterials, that beat the diffraction limit. Lensing effects have also been seen for negatively refracted acoustic waves. Recent theoretical work has begun to explore the phenomenon for liquid surface waves, and a team of researchers in France and the UK has now studied checkerboard lenses—arrays of square barriers in which either their edges or their vertices nearly touch. The team’s analysis revealed that at certain frequencies, concentric surface waves can be refocused beyond such lenses; those results were confirmed with simulations like the one shown here for two wave disturbances impinging on an array of 8.4-mm squares with nearly touching edges. The researchers say their analysis can also apply to electromagnetic waves propagating in square arrays of infinite-conductivity obstacles, to certain shear waves in elastic media with square-shaped cracks, and possibly to ultrasound tomography. (M. Farhat et al. , Phys. Rev. E , in press.)