Microphones and speakers in arrays known as mirrors can reflect and focus sound in a way that shows promise for fighting disease and other uses. Now, scientists have adapted the concept to work with electromagnetic waves, rather than sounds.
For more than a decade, Mathias Fink of the École Supérieure de Physique et de Chimie Industrielles in Paris and his colleagues have developed electronic mirrors that record sound echoes and then replay them in the reverse order of the way they were received. Known as time-reversal acoustics, the technique focuses the sound energy back to where it originated—a promising strategy for zapping tumors or other ailing tissue, pinpointing irregularities in materials, and funneling communications to selected listeners (SN: 3/15/03, p. 168: On the Rebound ).
The new work at the Paris lab examined electromagnetic signals at wavelengths typical of those of cell phones. A microwave antenna successf