Scientists from the University of Sussex have completed the “SoundBender”: which combines an acoustic meta-material with ultrasound transducer arrays to create a sound-based tractor beam that can levitate small objects from behind a solid object.
The new acoustic levitation device was Unveiled at the 31st ACM User Interface Software and Technology Symposium in Berlin. The target was small but significant enough to prove a principle. They levitated a polystyrene bead above a LEGO baseball figurine, passed sound-waves around a candle flame and even created a pressure point for haptic feedback – a way to vibrate air that could be useful, for simulating touch in virtual reality.
Dr Gianluca Memoli told Physics World. “A metamaterial is passive (like a lens for light), so we can theoretically put more energy in the sound,” “Each unit cell in the metasurface becomes like an additional source, which encodes phase engineering on the sound going through – just like an holographic plate. The only problem is that metamaterial-based holograms are static.”
Before the teams discovery scientists had attempted acoustic levitation via one of the two previously stated alternatives, neither of which could reach around solid objects to sustain levitation. The problem was that using metamaterials alone creates an immutable sound field geometry that cannot be adjusted. Whereas using only transducer arrays, you cannot bypass any obstacle within that acoustic field.
In the case of SoundBender, they combine both elements. The acoustic metamaterial contributes a low modulating pitch for immutable high resolution while the transducer array allows you to customize the amplitude and phase of each sound-wave. The combination of which appears to be ideal for this new kind of flexible acoustic levitation.
In particular they utilized a “metamaterial created from 16 different 3D-printed bricks on top of a programmable array of 16×16 off-the-shelf loudspeakers, operating at 40 kHz.”
Acoustic levitation is a continuing subject of interest for a purpose that may actually surprise you – water purification.