13 November 2019
By Gege Li
It is now possible to create a 3D moving image using nothing but a tiny polystyrene ball and an array of small speakers.
Ryuji Hirayama at the University of Sussex, UK, and his colleagues built the device from 512 speakers, positioned above and below a small 3D stage that acts as the image display. The speakers emit silent ultrasound to create small pockets of low air pressure in which the polystyrene ball floats. By manipulating the soundwaves emanating from the speakers, it is possible to rapidly shift the precise 3D position of the low-pressure pockets, and so control the position of the bead.
If the bead moves fast enough, it creates what appears to the viewer to be a 3D shape, and it is even possible to change the form of that shape over time to give the impression of a moving 3D object. But all this has to happen extremely quickly. The 3D shape has to be traced out in full in less than 0.1 seconds – any slower and the visual effect is lost.
It is even possible to add colour to the 3D objects by directing beams of red, green and blue light onto the bead.
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In one demonstration of the technology, the system shows a butterfly flapping its wings. In another, it shows numbers counting down to zero.
“It’s like magic,” says Hirayama, who was inspired by holograms and levitation depicted in popular films.
People are also able to touch the image. This works because the speakers create an area of higher pressure air that surrounds the bead. If someone reaches towards this area, it feels like they are touching the image, even though they are just touching air.
Asier Marzo at the Public University of Navarre, Spain, who has carried out similar work, says this new system is “way better” in terms of how fast the bead can move, allowing for more complex graphics.
Journal reference: Nature, DOI: 10.1038/s41586-019-1739-5
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