'We essentially created a virtual headset': Scientists transmit inaudible sound using ultrasonic beams to create single person 'audio enclaves'
Sound is a very strange thing. An echo-prone room can be fixed with a single bit of foam in a corner. Noise can be 'cancelled' by playing a reversed sound wave back at your ears. And now a new study has found that you can transmit sound across a room, even bending it around obstacles, so it can only be heard by someone standing in a specific spot.
A team of researchers at Penn State College of Engineering have been fine-tuning a technology that allows them to create 'audible enclaves' using nonlinear self-bending ultrasonic beams (via Futurism). And if that's all gobbledygook to you, allow me to explain.
Ultrasound is essentially sound with frequencies greater than 20 kHz, which often exceeds the limit of what can be heard by an average human being. The Penn State team has been using two beams of ultrasound waves to act as a carrier for audible sound.
They're silent to human ears until the point where they're forced to intersect, at which point the difference in frequencies, say, one at 40,000 Hz and one at 39,500 Hz interacts to create a new sound wave equal to the difference between the two—in this example, an audible sound at 500 Hz.
Yun Jing, professor of acoustics in the Penn State College of Engineering, explains the current methodology:
"We use two ultrasound transducers paired with an acoustic metasurface, which emit self-bending beams that intersect at a certain point. The person standing at that point can hear sound, while anyone standing nearby would not. This creates a privacy barrier between people for private listening."
Study co-author Jia-Xin Zhong continues: "We essentially created a virtual headset. Someone within an audible enclave can hear something meant only for them—enabling sound and quiet zones."
The effect is akin to someone throwing their voice, except instead of a creepy ventriloquist dummy as the recipient, it's you, perhaps standing in a museum looking at a painting and hearing a biography of the artist without interrupting other museum-goers.
More than that, however, the researchers say it's possible to use acoustic metasurfaces to bend sound in the same way that an optical lens bends light, meaning you could potentially manipulate these ultrasonic waves as they travel to avoid obstacles.
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Unfortunately we're probably still a long way off from an actual virtual headset, as the current method requires some bulky equipment directly behind your head and can only throw sound to around three feet, which is a bit of a shame.
Still, perhaps one day in the not so distant future we'll be beaming sound across rooms at each other with everyone else blissfully unaware.
Or, y'know, we could just wear a good set of headphones. Curses, I've ruined it, haven't I? Still, cool tech does cool tech things. Why let practicality get in the way of a good invention, that's what I say.