Pressure and phase characteristics of orbital angular momentum multiplexed perfect acoustic-vortexes

• Published in: Applied acoustics 2024-11, Vol.225, p.110168, Article 110168
• Main Authors: Yue, Wei, Chen, Wei, Liu, Yu-jin, Feng, Ting-zhen, Guo, Ge-pu, Ma, Qing-yu
• Format: Article
• Language: English
• Subjects: Angular phase slope; Circular segmentation; Orbital angular momentum multiplexing; Perfect acoustic-vortex; Topological charge difference
• ISSN: 0003-682X
• DOI: 10.1016/j.apacoust.2024.110168

•A simplified model of constructing OAM-multiplexed PAV is developed based on Bessel beams.•The circular lobe distribution in pressure and phase is only determined by differences of TCs.•Intensive changes of circular phase distribution are located at lobe boundaries of pressure valleys.•The pressure peak at φ = 0 increases as the TC number with the phase slope of the mean of TCs.•The remarkable lobe distribution may advance a fast and effective method for OAM communication. Profiting from the fixed vortex-radius, perfect acoustic-vortex (PAV) beams can improve the efficiency of orbital angular momentum (OAM) communication. While, characteristics of OAM-multiplexed PAVs with more than two topological charges (TCs) have not been studied. By applying the spatial Fourier transform to Bessel beams, the principle of constructing OAM-multiplexed PAVs is developed. The characteristics of OAM-multiplexed PAVs are investigated by theoretical analyses and numerical simulations, and also demonstrated by the experimental measurement based on quasi-Bessel beams constructed by the saw-tooth phase modulation for the ring-array of sectorial transducers. Numerical and experimental studies demonstrate that the high-pressure annuli are segmented to lobes, with the lobe number equal to the difference of the maximum and minimum TCs. Circular lobe distributions of pressure and phase only rely on TC differences, which may be identical for different TC combinations. The peak-pressure of the primary lobe centered at φ = 0 increases as the increase of the included TC number, with the angular phase slope equal to the arithmetic mean of included TCs. The excellent characteristics of the TC-independent vortex-radius and the remarkable lobe distributions of pressure and phase may guide the choice of TCs for encoding and decoding, and advance a fast, effective and low-cost method for underwater OAM communication.