Sound is indeed a peculiar phenomenon. An echo-prone space may be remedied with just a piece of foam set in a corner. Noise can be eliminated by playing back a reversed sound wave directly at your ears. Recent research indicates that sound can even be transmitted across a room by bending it around obstacles, making it audible only to a person positioned in a specific area.
A research team from Penn State College of Engineering has been refining a technique to establish ‘audible enclaves,’ utilizing nonlinear self-bending ultrasonic beams (via Futurism). If that sounds baffling, let me clarify.
Ultrasound consists of sound waves possessing frequencies that surpass 20 kHz, often going beyond the threshold of human hearing. The group at Penn State has been employing two beams of ultrasound waves to function as carriers for sounds audible to the human ear.
These waves remain silent to human perception until they intersect, where the frequency difference—say, one at 40,000 Hz and another at 39,500 Hz—merges to create a new wave that can be heard, equating to an audible sound at 500 Hz.
Yun Jing, who is a professor of acoustics, states that their current approach utilizes two ultrasound transducers in tandem with an acoustic metasurface, producing self-bending beams that meet at a designated point. Individuals located at this point can hear the sound while those nearby cannot, establishing a sound barrier for exclusive listening.
Co-author Jia-Xin Zhong explains: “We have effectively constructed a virtual headset. An individual within an audible enclave can hear sound targeted solely at them, facilitating sound and quiet zones.”
The outcome resembles the act of a ventriloquist throwing their voice, but instead of an unsettling puppet, it’s a person perhaps in a museum, engaging with a painting while listening to a biography of the artist without disrupting fellow visitors.
Moreover, the researchers assert that it’s feasible to manipulate acoustic metasurfaces to guide sound similar to how optical lenses manipulate light, enabling ultrasonic waves to navigate around barriers.
