The immediate vicinity of an oscillating source is filled by an evanescent standing wave whose energy dwindles to nothing within a wavelength or so. Although its range is feeble, the evanescent wave has one advantage over its propagating counterpart: It harbors information at scales finer than the oscillation wavelength.
Getting at that closely held and often valuable information usually entails bringing a lens or probe into the evanescent wave field itself. Near-field optical microscopes meet the challenge and provide subwavelength views of cells, nanocircuits, and other tiny objects.
Mathias Fink and his team from the University of Paris VII have built a simple yet ingenious antenna that draws the evanescent wave out of the near field and into the far field. When used in combination with a device called a time-reversal mirror, the antenna overcomes the diffraction limit and focuses microwaves onto a spot 1/30 of a wavelength wide. 1...
