Applied physics: Ultrasonic levitation from the side

Objects less than 1mm in size can be levitated, moved up and down, side-to-side, and rotated in a controlled manner with sound waves, reports a paper published online in Nature Communications. The study also reports the creation of acoustic structures such as tweezers, twisters and bottles, which can be used as so-called ‘tractor beams’ for container-less transport.

Ultrasound is made up of sound waves with frequencies above the limit of human hearing. These sound waves can be used in air, water or even tissue to levitate objects of different size and material, which means cells, liquids, compounds or living things can be manipulated without touching or contaminating them. However, acoustic levitation has so far required the target of the sound waves to be enclosed by the acoustic elements that emit the sound.

Asier Marzo and colleagues use an optimised ultrasonic phased array, where the timing of the sound waves is coordinated across multiple acoustic elements to show that acoustic levitation can be used to translate (move in one plane), rotate and manipulate particles with a diameter smaller than 1mm. They are able to achieve this with a single sided array, which sits on one side - not around - the target.

The authors propose the technology could one day prove useful for manipulating particles inside the human body and for targeted drug delivery, with other future applications including the development of powerful tractor beams and 3D physical displays.