In a breakthrough that could revolutionize personal sound privacy, scientists have developed technology to deliver private audio directly to a listener’s ears without the need for headphones. Researchers have been exploring various methods to precisely control sound waves using acoustic metasurfaces.
Private Audio Without Headphones: A Breakthrough in Acoustic Metasurfaces
Controlling sound has long been a staple of ‘science fiction and fantasy.’ In the real world, quirks of architecture can direct where sound goes. For instance, the U.S. Capitol’s hall of statues features curved surfaces that focus audio, allowing whispers to travel silently across the room.
Bending Sound Waves with Acoustic Metasurfaces
Scientists are developing technology to deliver private audio directly to a listener’s ears without the need for headphones. Researchers have been exploring various methods to precisely control sound waves. One approach relies on ultrasonic waves, which can be used to target audio thanks to an effect known as nonlinear interactions.
Ultrasonic waves are high-frequency sound waves with frequencies above human hearing range, typically above 20 kHz.
They are used in various applications, including medical imaging, cleaning devices, and non-destructive testing.
In medicine, ultrasonography uses these waves to produce images of internal organs and tissues.
Ultrasonic cleaning devices use the waves' energy to remove dirt and grime from surfaces.
The technology relies on the principle that high-frequency sound waves can create pressure waves in a medium.
When two ultrasonic waves meet, they ‘add’ together to create a higher-frequency wave. The converging waves also ‘subtract’ each other to create a lower-frequency wave that falls within the range of human hearing. This phenomenon is similar to tiny steam explosions generating ultrasonic waves in hot oil, which mix in the air to create the sizzle we hear.
Nonlinear interactions refer to complex relationships between variables where the output is not proportional to the input.
This occurs when small changes in one variable cause disproportionate effects on another, often leading to chaotic or unpredictable behavior.
In physics, nonlinear interactions are responsible for phenomena like turbulence and phase transitions.
In other fields, they can manifest as tipping points or sudden shifts in complex systems.
Private Audible Enclaves
Researchers have recently developed private ‘audible enclaves’ using acoustic metasurfaces. These materials are engineered to have tiny repeating structures that manipulate sound in ways natural materials can’t. A metasurface is a lens that’s thinner than the wavelength of the sound waves it manipulates, similar to lenses for light.
Jing and colleagues 3-D printed acoustic panels with zigzag air channels. By adjusting the path length of each channel, they steered ultrasonic waves into curved paths. The team then covered two speakers with thin sheets of this metasurface to bend the ultrasonic beams toward each other as they propagated through the air.
At the point of intersection, nonlinear interactions transformed the waves into audible sound that could be heard at only this spot. While the sound quality isn’t great, using a $4 transducer, Jing’s team has successfully demonstrated the feasibility of private audio without headphones.
Private audio refers to the use of encrypted and secure 'audio recordings,' allowing individuals to share confidential conversations without fear of eavesdropping.
This trend is driven by increasing concerns about data privacy and the need for secure communication methods.
According to a recent survey, 70% of businesses prioritize private audio solutions for sensitive discussions.
The technology behind private audio involves advanced 'encryption algorithms' and secure storage protocols, ensuring that recordings remain confidential.
Future Applications
This technology can’t create a ‘Dune-like cone of silence’ just yet, but the researchers envision a future where private conversations can happen in open spaces – no earbuds or wires required. Libraries, offices, and other public places could host numerous audible enclaves to allow for private audio streams simultaneously.
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- sciencenews.org | New audio tech could let you listen privately without headphones
