Broadband and tunable sound focusing

Acoustic metasurfaces with wavefront manipulation capabilities figure prominently in various applications, from ultrasound imaging and treatment to nondestructive testing. Boasting excellent acoustic properties, these 2D materials of subwavelength thickness can concentrate the energy of sound waves to form a high-energy area known as a “sound focusing” effect.

But traditional metasurfaces generally suffer from narrow bandwidth, untunable focus, and complex structures, all of which limit their practicality. The advent of coding metasurfaces, which enable real-time control of acoustic waves, has helped focusing functionality; and the more recent emergence of reconfigurable coding metasurfaces has enhanced tunability.

Building on these advances, Bai et al. integrated reconfigurability into a coding metasurface with an acoustic coding metagrating composed of rotatable open-ended round tubes for tunable broadband sound focusing. In simulations, adjusting the rotational angle of the open-ended round tubes enabled the metagrating to achieve precise focusing in both axial-axis and off-axis directions within the frequency range of 3400-5200 hertz.

“To further experimentally validate the sound focusing effect of our proposed metagrating, we fabricated the metagrating sample by 3D printing technology and established an experimental setup to measure the sound intensity field distribution,” said author Ailing Song.

The experimental results were consistent with the simulation results. The researchers verified their reconfigurable coding metagrating’s ability to precisely manipulate the focus by alternating the coding arrangements in a wide frequency range. Their work paves a promising path toward continued sound focusing performance improvement.

“We plan to extend this reconfigurable coding metagrating to other acoustic field manipulation applications, such as sound absorption, beam splitting, and acoustic holography,” said author Yanxun Xiang.

Source: “Broadband sound focusing with tunable focus based on reconfigurable acoustic coding metagrating,” by Yazhu Bai, Ailing Song, Chaoyu Sun, Yanxun Xiang, and Fu-Zhen Xuan, Applied Physics Letters (2023). The article can be accessed at https://doi.org/10.1063/5.0152748 .