A Self-focusing Vortex Acoustic Tweezers With Obstacle Avoidance Manipulation Function

Ultrasound is widely used in biomedicine because of its good penetrability.And the vortex beam is also a hot research topic in the acoustics with a spiral wave front,which can generate a potential well in the center,so that it is used to capture and rotate objects without contact.Combining it with some applications such as ultrasound therapy,targeted drug delivery,and ultrasound imaging can generate significant value in the fields of biomedicine,materials science,and information transmission.Compared with the traditional vortex beam which has the disadvantages of energy divergence,low precision and weak control ability,the focused vortex beam can concentrate the sound energy to the focal point,which contributes to a higher utilization rate,greater radial gradient force and axial acoustic radiation pull and thrust.Therefore,the focused vortex beam can achieve precise capture and positioning of objects.However,when there are obstacles in the propagation path,Absorption and scattering will cause beam distortion.And then they destroy the spiral phase and annular sound pressure distribution of the vortex acoustic tweezers,and seriously weaken the control ability.Therefore,it is of practical significance to construct a focused vortex acoustic tweezers with obstacle avoidance ability.In this paper,we use a radially symmetrical Half-Bessel beam and phase modulation to realize self-bending arc trajectory vortex beam and build a self-focusing vortex with a shape-controllable and close-to-zero pressure cavity,so it can realize obstacle avoidance control of objects.At first,the non-paraxial sound field distribution function with circular arc trajectory is derived from the Helmholtz equation,which proves the self-bending and non-diffraction characteristics of the Half-Bessel beam.Then,the phase distribution characteristics of the Half-Bessel beam are analyzed based on the 1D linear source.After introducing binary phase modulation,a Half-Bessel beam is generated in a 2D space through the groove structure;Furthermore,A circular phase modulation disc is constructed by rotating the 1D groove structure around the axis,and it is used to modulate the sound waves emitted by the planar sector transducer array.So we have formed a focused vortex with controllable topological charge on the propagation axis.Through numerical analysis,we evaluate the influence of parameters such as source size,hollow radius and topological charge on self-focusing vortex acoustic tweezers.Finally,we design 16-way phase control system,the 0,1 and 2 order self-focusing vortex acoustic tweezers was constructed by using the annularly distributed sector transducer array and the phase modulation disc manufactured by 3D printing technology.The amplitude and phase distribution are consistent well with the simulation results,and the particles are stably manipulated under different obstacle conditions.It proves the relationship between the capture radius of the focused vortex acoustic tweezers and the size of the manipulated object.According to theoretical and experimental results,the combination of active phase control and passive phase modulation can construct a self-focusing vortex acoustic tweezer with a controllable cavity.The radius of curvature of the trajectory is controlled by The order ? and the wave number k of Half-Bessel beam.The radius of transducer and the radius of the hollow determines the shape of the cavity and the focal position.It is found that the larger the radius of the transducer,the larger the angle at which the arc trajectory can be deflected.The larger the hollow radius,the longer the axial distance of the formed acoustic tweezers,and the larger the cavity size,the better the obstacle avoidance performance.The topological charge determines the order of the vortex acoustic tweezers,and also affects the vortex radius and the acoustic gradient force.The larger the topological charge of the focused acoustic vortex,the larger the manipulation radius and the smaller the manipulation force.In this research,the constructed self-focusing vortex acoustic tweezers with obstacle avoidance and manipulation capabilities can bypass obstacles to achieve noncontact acoustic manipulation.It can bypass bones or organs in biomedical applications,and realizes the accumulation of drugs behind them.At the same time,it can also combine with the acousto-thermal effect of the focused sound field to improve the therapeutic effect under the cooperation of ultrasound and drugs,which has great research significance and promotion value.