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. 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.