A focused beam of sound, just over an inch wide, could replace your headphones.
Penn State researchers have designed a system that manipulates sound waves to be audible only at a precise spot slightly wider than an inch, potentially enabling private, headphone-free listening. The work was published in IEEE Transactions on Ultrasonics.
Traditional sound waves spread outward from their source. Parametric array loudspeakers (PAL) use high-intensity ultrasonic waves to create a narrow beam of audible sound, but they can reflect off surfaces, reducing privacy, and struggle to produce low-end frequencies.
To address these issues, the team used acoustic metasurfaces, which are thin materials that can manipulate sound waves. The metasurface acts like a lens, focusing sound waves to converge at a central point, allowing audio to be directed to a precise area.