A Study On Object Manipulation Characteristics And Applications Of Vortex Sound Field

Due to the helical wave fronts and the central phase singularity,the acoustic vortex(AV)has been demonstrated to possess the capability of non-conatct object trapping in a rotation manner inside biological tissues,which has become to be one of the hot topics in the field of acoustics in the past decades.For the nondestructive penetrability of ultrasound,AVs can be combined with the applications of ultrasonic therapy,drug delivery and medical imaging,exhibiting a broad prospect in the area of biomedical engineering,materials science and information transmission.Many efforts have been focused on the studies of AV generation,orbital angular momentum transfer,acoustic radiation force and particle manipulation,etc.However,compared with the traditional model of ideal point source acoustic radiation,obvious discrepancies have been observed between theoretical and experimental results.Several influence factors ignored in previous researches,such as the directivity of transducers,the excitation of the ideal Bessel beam,the capability of axial manipulation of AV beams,are still the key issues to be resolved.In this paper,based on the analysis of the wave vector of AVs,the instantaneous orbital angular momentum and the acoustic radiation torque of AVs with different topological charge is firstly studied.The distributions of acoustic pressure and phase are simulated and the radiation torque exerted on the disk in various conditions is obtained as well.With the sixteen-source experimental setup,radius dependencies of radiation torque for AVs with different topological charges are verified by quantitative laser-displacement measurements.It is demonstrate that the radiation torque of AV is associated with the size of the object,which is more applicable than the orbital angular momentum in describing the driving capability of AVs.Secondly,by integrating the model of the directional source and phase-coded source array,deep-level stereoscopic multiple traps of AV are proposed to overcome the limitation of the point source model.The influences on the number and locations of vortex valleys taken by the directivity of the transducers are analyzed in detail.With the established eight-source AV generation system,the formed AV is measured,which achieve good agreements with simulations.It is demonstrated that,besides the main-AV generated by the main lobes of the sources,the side-AVs and the vortex valleys can also be produced by the side lobes with the number and locations can be adjusted by the physical parameter k₀b.To enhance the scope and the acoustic radiation torque for particle manipulation,the model of weak-focused acoustic vortex(WFAV)is proposed by considering the directivity and the elevation angle of the planar transducers for a circular source array.The acoustic scattering and the acoustic radiation force of a randomly placed elastic sphere in the WFAV is analyzed,representing the capability of object manipulation of WFAV in a large area.With the established 8-source array,the formation of WFAV are verified by the scanning measurement.The clear object rotation and motion of polyethylene particles in a 12 mm-diameter area are experimentally demonstrated.It is proved that acoustic radiation torque can be produced in a bigger area in the WFAV,which is beneficial to manipulating objects of a large scale in a large region.Finally,to further investigate the manipulation properties of AVs,a cone source model is put forward to simplify the model of WFAV.With the consideration of acoustic scattering,the acoustic radiation force of an elastic sphere in the WFAV is theoretically studied,and the corresponding acoustic radiation torque and the axial radiation force are deduced in analytic solutions.Based on the simulation of the scattered velocity potential,the distributions of the acoustic radiation torque and the axial radiation force in various conditions are achieved,providing the basis for the design and the optimization of AVs for biomedical applications.In this thesis,the generation method and the characteristics of both the audio AV and ultrasonic AV are investigated.With the analysis of acoustic radiation force and the rotation torque,the physical mechanism of object manipulation using AV beams is interpreted,and the theory and technology of AV is consummated as well.Object manipulations of particle rotation and motion in a large area using the proposed WFAV are demonstrated and the optimization of AV beams is also realized by adjusting the parameters of the source array.Favorable results provide theoretical and experimental bases for three-dimensional stable object manipulation and promote the practical applications in ultrasound therapy.