Interactive Hologram Uses Ultrasound Waves and LEDs

Researchers at the University of Sussex have built a device that uses LEDs and ultrasound waves to levitate a polystyrene bead and create tactile, 3D holograms.

A holographic butterfly created by a vibrating polystyrene bead and LED lights flutters inside the MATD. Courtesy of Ryuji Hirayama, University of Sussex.

The device, known as a Multimodal Acoustic Trap Display (MATD), maneuvers the 2-mm-wide bead at up to 20 mph, tracing shapes in the air colorized by the LEDs. At this speed, human brains are unable to perceive the bead moving and instead see the shape it creates.

By vibrating the bead in its flight pattern, the scientists were able to transmit speech, sound effects, and music through the holograms. The manipulated sound field also allows the holograms — in one example, a butterfly — to be felt by hands by raising the air pressure around the bead.

“Our new technology takes inspiration from old TVs that use a single color beam scanning along the screen so quickly that your brain registers it as a single image,” said Ryuji Hirayama, lead author of the study. “Our prototype does the same using a colored particle that can move so quickly anywhere in 3D space that the naked eye sees a volumetric image in mid-air.”

Hirayama and his colleagues built the device from 512 speakers positioned above and below a small 3D stage that acts as the image display. Hirayama said it had been a long-term dream to make such a device. But he sees this as a step toward more sophisticated systems. “I believe that in the future, such displays will allow us to interact with our family and friends as if they are close by, so you can see, touch, and hear them,” he said.

Julie Williamson of the University of Glasgow said levitating displays are a step closer to interactive 3D images. “I imagine a future where 3D displays can create experiences that are indistinguishable from the physical objects they are simulating,” she said.