Study On The Generation And Regulation Of Acoustic Vortex States

As a common information carrier and energy carrier,acoustic wave has always been one of the hotspots of physics research.Especially in the information era,acoustic wave has lots of important applications in the development of human society,such as information communication,medical imaging,military weapons and electronic products and so on.Vortex,as a special form of sound wave,has zero field intensity along the central axis of the propagation direction(We generally call this center as a phase singularity point).while the phase along the axis of the zero field intensity center presents a spiral change in the radiation angle.In addition,the pressure field formed by the acoustic vortex has orbital angular momentum.When we apply it to a small object,the acoustic wave of the vortex will exert a moment on the object and make it rotate locally near the phase singularity.By using this characteristic,the location and manipulation of the contactless drug particles can be realized in the direction of medical application.However,the conventional sound wave is a longitudinal wave,and there is no transverse mode.Therefore,how to convert the conventional sound wave into vortex sound wave through manual control is the subject of this paper.Starting from the historical background of the research on acoustic vortex,this paper briefly summarizes several methods of generating acoustic vortex in recent years,and compares the advantages and disadvantages of them.Subsequently,we propose two kinds of new methods to generate acoustic vortex,elaborating on their physical mechanism and design scheme in detail.We use numerical software to simulate the generation of acoustic vortex.The following are the main innovations of this paper:(1)A leaky wave antenna structure based on circular waveguide is constructed.The structure has circular perforations with uniform distribution on the upper surface of the annular waveguide.Acoustic wave propagates along the waveguide through circular perforation in turn with continuous variation of wave path difference,which results in the continuous phase difference of the acoustic wave radiated from each perforation,and then forms acoustic vortex with a phase spiral distribution.This method is easy to implement in geometric configuration,and the order of acoustic vortex is adjustable.We only need a transducer to generate acoustic vortex with different acoustic topological charge by changing the frequency of incident wave.This method not only overcomes the array complexity of active phase system,but also avoids the cumbersome steps of passive coding of signal channel.At the same time,we introduce standing wave effect based on this structure,and form a space with zero field intensity at the axis of the propagation center combining with the acoustic vortex field,which provides a new design idea for the capture of particles by acoustic wave.(2)We design a waveguide cavity structure with sub-wavelength size,which can separate the degenerate helical modes of high-order waves propagating in cylindrical waveguides.According to the functional characteristics of acoustic waveguide modes in waveguides,we design a circular saw-tooth structure on the wall of the cavity.Through the analysis and calculation,the saw-tooth structure can separate the deviations of the high-order degenerate modes produced in cylindrical waveguides.The separated high-order harmonic modes themselves are a kind of vortical sound waves.In this way,the positive and negative torque that should cancel each other can be separated,and the particle can be manipulated by using this torque.This method provides a simpler design idea for generating acoustic vortex,and can be applied to high-density integrated systems because the structure size is in the sub-wavelength range.