We have heard about optical metamaterial and how such materials can become left-handed and also defeat the diffraction limit. Well now, an acoustic metamaterial made up of soft drink cans (link open for free only for a limited time) has been made, and it can defeat the acoustic diffraction limit!
Lerosey and his colleagues took a similar approach to an experiment they performed in 2007 and later described theoretically for electromagnetic waves1,2. The group generated audible sound from a ring of computer speakers surrounding the acoustic 'lens': a seven-by-seven array of empty soft-drink cans. Because air is free to move inside and around the cans, they oscillate together like joined-up organ pipes, generating a cacophony of resonance patterns. Crucially, many of the resonances emanate from the can openings, which are much smaller than the wavelength of the sound wave, and so have a similar nature to evanescent waves.
To focus the sound, the trick is to capture these waves at any point on the array. For this, Lerosey and his team used a method known as time reversal: they recorded the sound above any one can in the resonating array, and then played the recording backwards through the speakers. Thanks to a quirk of wave physics, the resultant waveform cancels out the resonance patterns everywhere — except above the chosen can.
The work will be published in PRL (I'll put a reference to it here when it is published).
Edit: A review of this work can be found on PhysicsWorld website.