Scientists Create Mind-blowing 3-D Acoustic Holograms

Duke University engineers have created a method to alter sound similar to how holograms alter visible light. Mehau Kulyk/Science Photo Library/Getty Images

Imagine a tiny, glowing Princess Leia pleading for help from Obi Wan Kenobi in "Star Wars," you've got the general idea of what a hologram is —manipulated light that appears as a three-dimensional object in what actually is empty space. Hologram-creating devices reshape electromagnetic fields, to create the illusion that light is bouncing off an actual thing or person.

Holograms have been around for decades. But now, Duke University engineers have given the notion a new wrinkle, by figuring out how to create acoustic holograms — that is, sound that gives the illusion of existing in three dimensions.

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

Think of it this way — you could either walk through a room full of acoustic holograms, experiencing different sounds and noises in different places but not others, or the holograms could be programmed to be projected in different places as you sat still (in front of a TV, perhaps), making it sound like a hyper-realistic surround-sound system. And, in theory, a constant unchanging soundwave projected through the device could be changed as the device changed, like an audio version of a light machine equipped with different filters to change colors.

This new device alters soundwaves to create what scientists are calling an "acoustic hologram."
Steve Cummer/Duke University

The gadget itself looks a bit like a wall made from Lego bricks, but it's actually composed of 3-D-printed metamaterials — that is, synthetic stuff made from a multitude of individually engineered tiny cells that when combined feature amazing properties. Basically, each of the bricks contains a spiral, which affects the way that sound moves through it. In combination, the slight differences between the blocks can redirect the sound wave, so that it bends whichever way the designers want it to go.

A computer rendering of the 12 different kinds of spirals contained in the metamaterial blocks. Each slows sound waves by different specific amounts, and organizing the spirals in an array bends the shape of incoming soundwaves.
Steve Cummer

"It's basically like putting a mask in front of a speaker," Cummer said. "It makes it seem like the sound is coming from a more complicated source than it is."

The technology, described in a new article in the journal Scientific Reports, could make future stereo systems and speakers super-vivid, which is great for audiophiles, but the scientists also say there see potential applications in medical ultrasound devices.

A sound wave that traveled through an array of acoustic metamaterial could be shaped into a pattern, as in this rendering. The "hologram" would be invisible like all soundwaves, and could only be heard.
Steve Cummer/Duke University

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