Sonic Tractor Beam...

Sound image: the acoustophoretic display reproduces the logo of the University of Bristol. (Courtesy: A Marzo, B Drinkwater and colleagues)

Topics: Acoustic Physics, Holograms, Research, Star Trek

A midair visual display that uses a single acoustically-levitated particle has been unveiled by researchers in Spain and the UK. Dubbed an “acoustophoretic display”, the image is created by using two ultrasound transducer arrays to levitate the particle and manipulate it to trace out the desired graphic at high speed.

In 2015, Asier Marzo at the Public University of Navarra and Bruce Drinkwater at the University of Bristol created a sonic tractor beam that used ultrasound to levitate, rotate and move objects. Using a single grid of 64 off-the-shelf loudspeakers controlled by a programmable array of transducers the device created 3D fields of sound – acoustic holograms – that could hold and manipulate a small polystyrene particle in mid-air.

Since then, the field has progressed and earlier this year Marzo and Drinkwater revealed an acoustic levitation device that used two grids of speakers to hold and individually manipulate up to 25 polystyrene balls at the same time. This opened up the possibility of new applications for sonic tractor beams, including visual displays created with multiple levitated particles.

According to Marzo, such acoustic generated images, which he calls acoustophoretic displays, would offer an advantage over current holograms as they would not suffer from clipping. “[With holograms] the image can only be viewed from determinate angles and the frame of the display occludes the image, it is like looking inside a window,” he explains. “With the acoustophoretic displays the images reside in the physical space and can be observed without clipping from 360°.”

Ultrasound guides particle in a midair display, Michael Allen, Physics World