If you thought acoustic levitation was nifty, wait till you see this: moving a small bead in arbitrary directions with a holographic sound field.
Say what? By varying the phases of an array of 64 ultrasonic transducers, researchers at Spain’s Public University of Navarre were able to create ‘acoustic objects’: three-dimensional patterns of air compression that can push against a lightweight object. The video above depicts the ‘twin trap,’ which is pretty much like invisible tweezers. Even more impressive than that is the ‘bottle trap,’ which creates a complete enclosure around the specimen, allowing you to move it wherever you want.
What’s particularly unique about this experiment is that it considers the acoustic field above the transducers as, literally, a hologram: a projection of a two-dimensional surface that utilizes interference patterns to create a three-dimensional field.
Prior work in this field relied on either standing waves (as previously posted) or Bessel beams, which are able to pull on specially contrived objects. All of these approaches have a myriad of possible uses, but the new ‘holographic’ field may be the most flexible:
The introduction of three acoustic structures for the translation and rotation of levitated particles will find applications in tractor beams, containerless handling of matter and tangible displays. Our systems use inexpensive low-power transducers but high-power versions could enable longer range 3D transportation, orientation and assembly of heavier objects. Single-sided devices potentially enable in vivo manipulation since the device could be applied directly onto the skin with the manipulation taking place inside the body
Lots more amazing detail in their paper in Nature.