Research On Acoustic Vortex Field And Its Orbital Angular Momentum Technique

An acoustic vortex is a beam that spirals along a central axis with a helical phase and a strong zero central voice.The unique acoustic field characteristics and orbital angular momentum of vortex beam lead to its wide application prospects in particle control and acoustic communication fields.Based on this,this thesis focuses on the generation mechanism of acoustic vortices,the influence parameters of the acoustic field of vortices,the principle of orbital angular momentum coding and decoding and experimental methods,and so on,to explore a new acoustic communication method.According to the basic theory of acoustic vortex,the formation mechanism and influence parameters of acoustic vortex field are analyzed and studied.An array acoustic vortex field model composed of 16 array elements was established,and the influence mechanism of different topological charge numbers and student frequency on the shape of vortex sound field was analyzed.Type of topological charge number instead the topological charge number vortex beam,symbols two-phase deformed double topological charge number of vortex beam and sign the same double topological charge number vortex has carried on the simulation analysis and research of the beam,the analysis results show that the topological charge number vortex and the vortex vortex beam has center,its unique sound field form for orbital angular momentum decoding method to provide theoretical and experimental basis.Based on the bistopological load number vortex beam,the feasibility of using orbital angular momentum as the orthogonality basis for acoustic communication is studied.On the basis of amplitude modulation and orbital angular momentum coding,two encoding methods,amplitude-OAM coding and high-low bit-OAM coding,are proposed to solve the problem that orbital angular momentum coding is limited by the number of sound sources.Finally,according to the above research contents,a 16-channel ring transducer array experimental system was built.Firstly,the influence of sound source frequency and topological charge number on vortex sound field was verified and compared with the simulation results:The simulation results and experimental data have a high degree of consistency,that is,at the frequency of 1000 Hz and the radius of the sampling ring of300 mm,the shape of the acoustic vortex is more suitable for the orbital angular momentum coding and decoding experiments.Based on this,the orbital angular momentum codec experiment was carried out.The experimental results show that under the condition of a threshold of 0.5,the invalid data in the decoded histogram is distributed between,while the effective data is distributed between.The experiment shows that the two kinds of data can be distinguished effectively under the condition of small channel disturbance and limited number of sound sources,which verifies the feasibility of applying OAM-coding and high and low bit-OAM coding to acoustic communication.In conclusion,the effects of topological charge number and sound source frequency on the amplitude and phase of acoustic pressure are clarified through the study of acoustic vortex field,which provides a simulation and experimental basis for the influence mechanism of the shape of acoustic vortex field.The study of orbital angular momentum codec on the basis of bistopological load number vortex beam explores the feasibility of orbital angular momentum as a new degree of freedom in acoustic communication.