Tunable orbital angular momentum generator for directional acoustic transmission

Underwater acoustic propagation has emerged as a focal point of research across various fields due to its low attenuation characteristics, particularly in applications such as underwater detection, monitoring, and imaging. Based on the orbital angular momentum (OAM) degree of freedom, an intriguing technique known as the acoustic vortex (AV) based communication is developed to enhance underwater communication capacity. At present, precise directional information transfer and concentration of signal intensity are crucial to guarantee the performance of underwater AV communication. Considering that the vortex beams with curved or inclined trajectories could exhibit unique advantages in resolving the scenarios like the obstacles obstructing the propagation path, this paper intends to offer a general scheme to actively tune the propagation of the AV beam with a reconfigurable directional signal transmission device, which could effectively improve the performance of OAM-based underwater communication systems. Here, we combine two gradient lenses and a circular sawtooth lens on top of an active circular phased array, where the center of emitted quasi-Bessel AV beams can be transferred to any position in a two-dimensional plane. In comparison to traditional off-axis AV beam construction methods, our work could actively adjust the transmission direction and deliver the highly concentrated signals to the target receiver's location, which exhibits lower costs and greater flexibility, holding promising prospects for widespread applications in the field of acoustic communication.