Metamaterial ‘Lego’ blocks create 3D acoustic holograms

computer rendering of a sound wave shaped in 'A' pattern in 3D acoustic hologram by duke university
Computer rendering of a sound wave shaped like letter 'A,' 30 cm from acoustic metamaterial array

Visual holograms or ‘hologram’-type displays may often be in the news, but researchers at Duke University have announced an interesting breakthrough in acoustic hologram technology.

Researchers from the university in North Carolina have unveiled how metamaterial building blocks (think 3D-printed plastic Lego) can be used to create acoustic holograms by placing them in front of sound wave – and best of all, the ‘holograms’ are also energy efficient.

Engineers are able to create complex soundscapes from arrays of 3D printed metamaterial blocks that sit in front of a speaker. Just like how visual holograms are produced by shaping an electromagnetic field that mimics light bouncing off an item, pressure waves that create sound are manipulated to create a 3D pattern.

The research team state they have been able to manipulate the technology to concentrate on multiple loud spots of sound and even have created letters (such as “A”) from approximately 30 cm (1 foot) away from the acoustic metamaterial array.

"We show the exact same control over a sound wave as people have previously achieved with light waves," commented Steve Cummer, professor of electrical and computer engineering at  Duke University. "It's like an acoustic virtual reality display. It gives you a more realistic sense of the spatial pattern of the sound field."

Each individual block of 3D plastic has one of twelve types of different spiral shapes within it, with the tightness of the spiral which slows sound by a specific amount (i.e. the tighter the spiral, the more it slows sound waves). By forming a structure of different blocks, operators can use the device to shape the direction of an incoming wave and therefore organise them to create a specific “acoustic hologram” a particular distance away.

In contrast to similar technologies such as ultrasound imaging, the team at Duke University say the system can be used to the same effect at a considerably lower running cost due to its energy efficiency.

Researchers are currently investigating how best to apply the acoustic hologram technology, and are hopeful that it could be of benefit to medical imaging applications.

"Any scenario where your goal is to control sound, this idea could be deployed. And it could be deployed to make something totally new, or to make something that already exists better, simpler or cheaper,” said researcher at Duke University, Yangbo "Abel" Xie.

Source: News Atlas