In a groundbreaking development within the field of acoustics, researchers have successfully generated three-dimensional spatiotemporal acoustic vortices capable of carrying arbitrarily oriented orbital angular momentum (OAM). This achievement, detailed in a recent study published in Nature Communications, marks a significant stride in the manipulation of acoustic waves, enhancing both scientific understanding and potential applications.
Acoustic vortices are characterized by their unique spiral phase distribution and doughnut-shaped intensity profile. Traditionally, these vortices have only carried longitudinal OAM aligned with their direction of propagation. However, this new research enables the generation of spatiotemporal (ST) acoustic vortices featuring transverse OAM, which can rotate in three-dimensional (3D) space.
By employing a two-dimensional (2D) acoustic phased array comprised of 121 loudspeakers, the research team introduced novel methods to manipulate the orientation of OAM. One approach involves the direct rotation of vortices in 3D space, while the other takes advantage of the intersection of vortices carrying distinct types of OAM. This advancement in controlling the orientation of acoustic OAM provides greater flexibility for the manipulation of acoustic waves, with implications for various applications, including advanced particle manipulation techniques.
The experiments were conducted in an anechoic chamber, which is specially designed to eliminate sound reflections. The setup utilized a grid of speakers arranged with a spacing of 5.5 cm, allowing precise adjustments to the amplitude and phase of each loudspeaker. This configuration enables the construction of complicated acoustic wave packets, or ST wave packets, from a total of 2,744 distinct plane wave modes.
During the study, the team generated both longitudinal and transverse OAM, with the resulting wave packet exhibiting a spatial width of approximately 70 cm and a temporal duration of around 2 ms. The central frequency used was 4100 Hz, correlating to a wavelength of 8.4 cm. The researchers also measured the intrinsic OAM, defining the tilted wave packet’s OAM as (0,√2/2,√2/2) after a 45-degree rotation around the x-axis.
Moreover, the research outlines how the orientation of OAM can be altered through the integration of vortices with different types of OAM, effectively allowing for the manipulation of the OAM components within the wave packet. For example, their calculations confirmed that a wave packet combining OAM from multiple vortices could generate complex zero-amplitude tunnel structures, vital for experimental and applied acoustics.
“This innovative work establishes a foundation for future explorations into the complex dynamics of novel structured acoustic fields in the spatiotemporal domain,” wrote the authors of the article. They emphasized the findings’ far-reaching implications, suggesting they could influence techniques used for acoustic trapping and other salient methodologies in the field of acoustics.
The establishment of 3D ST acoustic vortices not only extends our fundamental understanding of acoustic OAM but also paves the way for novel applications that can leverage these unique properties. As our capacity to manipulate sound waves progresses, potential benefits may be heralded in fields such as information transmission and non-invasive object manipulation.
Overall, this research heralds a new era in the field of acoustics, opening numerous pathways for scientific inquiry and technological advancement. The exploration of 3D ST vortices could result in significant developments in areas that necessitate sophisticated control of wave phenomena, including acoustical engineering, communication, and particle science.
