Periodic-Phase Acoustic Vortices with Tunable Comblike Orbital Angular Momentum Spectrum

Acoustic vortices (AVs) carrying orbital angular momentum (OAM) have shown great significance in communication. However, crosstalk in acoustic communication based on traditional AVs with single OAM remains an issue. Here, we propose a periodic-phase acoustic vortex (PPAV) with a comblike OAM spectrum. The sample interval of the OAM spectrum of the PPAV can be modulated by the period number of the azimuthal phase. The influence of the period number on the acoustic properties of the PPAV and the evolution of the PPAV are investigated theoretically. Moreover, an acoustic artificial-structure plate engraved with 24 filled circular holes is designed to generate the PPAV in water. By changing the height of the resin layer filling each hole unit, the transmitted phase shift of the ultrasonic wave through them can be flexibly and efficiently manipulated. Both simulations and experiments confirm that the designed artificial plate with filled holes can produce the PPAV with an arbitrary topological charge. Finally, we preliminarily explore the possibility of applying the PPAV in acoustic communication and show that the OAM sample interval of the PPAV can be used as an independent degree of freedom for acoustic encoding decoding communication. We believe that the PPAV generated by the acoustic artificial-structure plates may find good applications in microparticle manipulation and acoustic communication.