Gao Shuxiang, Li Yunbo, Ma Chengrong, Cheng Ying, Liu Xiaojun
Key Laboratory of Modern Acoustics, Department of Physics and Collaborative Innovation Center of Advanced Microstructures, Nanjing University, Nanjing, China.
State Key Laboratory of Millimeter Waves, Southeast University, Nanjing, China.
Nat Commun. 2021 Mar 31;12(1):2006. doi: 10.1038/s41467-021-22325-7.
Recent years have witnessed a rapidly growing interest in exploring the use of spiral sound carrying artificial orbital angular momentum (OAM), toward establishing a spiral-wave-based technology that is significantly more efficient in energy or information delivering than the ordinary plane wave technology. A major bottleneck of advancing this technology is the efficient excitation of far-field spiral waves in free space, which is a must in exploring the use of spiral waves for long-distance information transmission and particle manipulation. Here, we report a low-profile planar acoustic antenna to modulate wavefronts emitted from a near-field point source and achieve far-field spiral airborne sound carrying OAM. Using the holographic interferogram as a 2D modulated artificial acoustic impedance metasurface, we show the efficient conversion from the surface wave into the propagating spiral shape beam both numerically and experimentally. The vortex fields with spiral phases originate from the complex inter-modal interactions between cylindrical surface waves and a spatially-modulated impedance boundary condition. This antenna can open new routes to highly integrated spiral sound emitters that are critical for practical acoustic functional devices.
近年来，人们对探索携带人工轨道角动量（OAM）的螺旋声音的应用兴趣迅速增长，目的是建立一种基于螺旋波的技术，该技术在能量或信息传递方面比普通平面波技术效率更高。推进这项技术的一个主要瓶颈是在自由空间中高效激发远场螺旋波，这对于探索将螺旋波用于长距离信息传输和粒子操纵来说是必不可少的。在此，我们报道了一种低剖面平面声学天线，用于调制从近场点源发射的波前，并实现携带OAM的远场螺旋空气声。利用全息干涉图作为二维调制人工声阻抗超表面，我们在数值和实验上均展示了从表面波到传播的螺旋形波束的高效转换。具有螺旋相位的涡旋场源于圆柱表面波与空间调制阻抗边界条件之间复杂的模式间相互作用。这种天线可为高度集成的螺旋声音发射器开辟新途径，而这种发射器对于实际声学功能器件至关重要。
