2025-03-17 ペンシルベニア州立大学（PennState）
By positioning metasurfaces in front of two ultrasonic transducers, dual ultrasonic waves travel at two slightly different frequencies along a crescent-shaped trajectory until they intersect, forming an audible enclave where sound cab be heard. At other points along the trajectory, sound is not heard — meaning private listening is possible. Credit: Provided by Heyonu Heo. All Rights Reserved.
＜関連情報＞
- https://www.psu.edu/news/engineering/story/audible-enclaves-could-enable-private-listening-without-headphones
- https://www.pnas.org/doi/abs/10.1073/pnas.2408975122
非線形自己屈曲超音波ビームによって作られる可聴領域 Audible enclaves crafted by nonlinear self-bending ultrasonic beams
Jia-Xin Zhong, Jun Ji, Xiaoxing Xia, +1 , and Yun Jing
Proceedings of the National Academy of Sciences Published:March 17, 2025
Significance
Recent advancements in digital signal processing and loudspeaker array design have enabled us to experience immersive spatial audio in virtual/augmented/extended reality environments in our daily lives. However, further development in audio engineering is impeded by physical constraints stemming from the diffraction of long-wavelength audio waves. This study introduces an approach to address this issue by showcasing the creation of ultrabroadband (125 Hz to 4 kHz) and highly localized remote audio spots, referred to as audible enclaves. By marrying local acoustic nonlinearity with inaudible self-bending ultrasonic beams, the proposed technique overcomes the physical limits in linear acoustics, paving the way for possibilities in future audio engineering.
Abstract
Delivering audible content to a targeted listener without disturbing others is paramount in audio engineering. However, achieving this goal has long been challenging due to the diffraction of low-frequency (long-wavelength) audio waves in linear acoustics. Here, we introduce an approach for creating remote audio spots, dubbed audible enclaves, by harnessing the local nonlinear interaction of two self-bending ultrasonic beams with distinct spectra. The self-bending ultrasonic beams created by acoustic metasurfaces, though inaudible, can bypass obstacles such as human heads. At their intersection behind obstacles, highly localized audible enclaves are formed due to the local nonlinear interactions. Additionally, we demonstrate the ultrabroadband capabilities of our metasurface-based implementation both numerically and experimentally, spanning from 125 Hz to 4 kHz (6 octave bands), covering the majority of the audible frequency range. The practicality of our proposed technique is underscored by its compact implementation size (0.16 m, equivalent to 0.06 wavelengths at 125 Hz), as well as its robust performance under wideband transient audio signal excitation and in a common room with reverberations. Our proposed audible enclaves hold significant potential for various applications in advanced audio engineering, including private speech communications, immersive spatial audio reproduction, and high-resolution sound/quiet zone control.
