Nature Mater. doi:10.1038/nmat2561 (2009)

Whether it be light or sound, there is a limit to the detail a lens can resolve. Because of diffraction, a conventional lens will never resolve features smaller than about half a wavelength.

But this rule doesn't hold for lenses made of metamaterials, composite materials that bend light or sound waves in unusual ways. Xiang Zhang and his colleagues at the University of California, Berkeley, used 36 precisely machined brass fins to create just such a lens for sound waves. Their 'hyperlens' compresses evanescent sound waves, which fade away very quickly, into more robust propagating waves, magnifying sub-diffraction features by a factor of eight. The technology could lead to higher-resolution images in sonar and ultrasound.