Researchers at Penn State University have recently taken huge steps in creating an innovative new audio technology. If successful, this innovation has the potential to dramatically improve how people experience sound in public spaces. This novel technology uses lasers to steer sound waves, producing an unparalleled, exclusive listening experience with the absence of headphones.
In 2019, scientists stumbled onto an exhilarating find. They first discovered that lasers could steer sound by turning light into sound, specifically sound that is absorbed by atmospheric water vapor. Thumbs up from Penn State Yun Jing, an acoustics researcher at Penn State, stressed that this technology was “like wearing an invisible headset.” The concept is simple yet groundbreaking: it allows sound to be directed toward specific individuals while leaving those nearby unaware of what is being heard.
Although full of potential, the technology isn’t without limitations. Jing mentioned that the audio fidelity is pretty terrible. This is largely due to the fact that they employed a low-cost $4 transducer in their experimental setup. This component is vitally important to creating sound, but it doesn’t create clear audio.
This technology addresses a major public safety concern. It does this by looking to minimize how easily sound frequencies fall between 20 to 20,000 hertz, which is within the human hearing range, dissipate into the surrounding environment. This diffusion will result in the audio content being audible, disrupting the private content consumption experience that these devices were designed for. To mitigate this, scientists are adjusting their approaches to provide private audio directly to listeners while outside in public spaces.
Jing’s team has come up with an approach that could be used to cloak just two speakers with thin sheets of metasurface. These curved surfaces are used to focus ultrasonic beams together. When two ultrasonic waves converge, they negate one another. This interaction produces an infrasound wave, a wave at a lower frequency than the sound waves humans can hear. Depending on how someone chooses to seat themselves, they can be surprised by the musical sounds or poetry. Those living nearby will not have an opportunity to hear a peep.
To dive deeper into the ideas behind metasurfaces, we spoke to Michael Haberman, a mechanical engineer at the University of Texas at Austin. He described them as “a lens that’s thinner than the wavelength of the sound waves it manipulates.” This development is important not only for directing sound direction, but generally enhancing the usefulness of the technology.
To make their experiments more immersive, Jing’s team 3-D printed acoustic panels with zigzag air channels. We hope to use this unique design to gain more control over the propagation of sound waves. When two such ultrasonic waves meet, they interlace to produce a new wave of higher frequency. This union brings your personal listening experience to life like never before.
The consequences of this development go much further than an afternoon listen. For instance, a whisper might easily soar over the expanse of a room. This extraordinary phenomenon was brilliantly featured on the honor wall located in the U.S. Capitol’s hall of statues. This ability might have far-reaching implications across domains from security to communication.
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