“Audible enclaves” are what researchers at Penn State have called their fascinating new technology that can direct sound at a single person, even if they’re standing in a mass of people.
Publishing their research in Proceedings of the National Academy of Sciences, the Penn State researchers demonstrate that their technology can manipulate ultrasound waves to create pockets of sound that only a specific person can hear, and all without headphones.
Ultrasound waves are frequencies above the human hearing range and are normally used in medical imaging and various other industrial applications. Researchers Jiaxin Zhong and Yun Jing have turned ultrasound waves into a carrier for sound, enabling a sound to travel silently until it reaches a specific target. Standing in the way of this sound beam wouldn’t cause you to intercept the sound either, because the sound can bend around you like the bullets in Wanted.
They accomplished this wild feat by using not one beam of sound but two. By firing two ultrasound beams of different frequencies at a single target, the two combine to create an audible frequency equal to the difference between the beams, settling the sound within the range comfortable for human ears. The sound is only audible at the point where the two beams intersect, hence the “enclave.”
And then there’s the matter of getting the sound to bend around objects that would otherwise prevent the beam from reaching its destination, a.k.a. diffraction. To figuratively and literally get around this, the researchers used what they call “acoustic metasurfaces,” a specialized material that can shape the path ultrasound beams take as they travel through the air.
Think of it like how the placement of a Major League Baseball pitcher’s fingers can alter the path of a thrown ball to befuddle a batter. Sure, you can just barehand grip it and rip it, or you can strategically place your fingers along specific parts of the ball that change the direction the ball breaks as it cuts through the air. Similar idea. By throwing the sound a specific way, they were able to navigate around obstacles and reach their desired target.
The technology is still in its infancy and probably won’t be seen anywhere in public for quite a while, but that hasn’t stopped the researchers from fantasizing about all its different applications.
They imagine museum tours where you don’t need a headset and a little MP3 player, but instead, a complex audio system beams the guided tour voice directly into your ears as you wander the show floor. The common annoyances of family road trips could be wiped away as the driver who wants to sit in silence as they focus on the road wouldn’t have to listen to the 12th episode of Bluey playing for their kids in the backseat.
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