Construction Of Ultrasonic Phased Array Acoustic Tweezers And Study Of Droplet Dynamics In The Acoustic Field

Industrial-grade array piezoelectric micro droplet 3D printing technology can produce high-precision,complex structured parts and components in a very short period of time,and has shown great potential for a wide range of applications in advanced manufacturing.The quality of printed parts is closely related to the droplet quality,but adjusting the morphology and jet speed of printed droplets by waveform parameter adjustment and waveform optimization is not a once-and-for-all solution.In this paper,we propose a universal method of ultrasound-assisted droplet manipulation to solve the conflict between injection speed and droplet morphology control based on the action mechanism of ultrasound on fluid.As one of the non-contact ultrasonic manipulation techniques,standing wave acoustic tweezers are used to move and manipulate droplets by forming a high-intensity standing wave acoustic field and using acoustic radiation force,but holographic manipulation cannot be achieved due to the structural limitations of the device,and the scope of application is limited.Further,on the basis of overcoming the limitations of the use scenario of ultrasonic phased-array standing-wave acoustic tweezers with symmetric concave spherical surfaces on both sides,the construction method of unilateral phased-array traveling-wave acoustic tweezers is proposed,i.e.,the holographic manipulation of the levitated target is realized by using only a unilateral transducer array through the phase modulation technique.The details of the work are shown as follows.Firstly,the discussion of the combined form of the composite array print head with the introduction of ultrasound assistance is initiated,and two control schemes of standing wave field and travelling wave field are formulated.The classical ultrasonic radiation force theory approach of King and Gor’kov is used to derive the forces on the levitated object under acoustic conditions.The principles of standing wave and traveling wave acoustic tweezers generation are analyzed based on the theoretical approach.The principle of phased array time-delayed focusing is described,and the radiation model of the transducer array is constructed.Next,the calculation method of array emission delay in different dimensions is derived by using the time inversion method.The biconcave spherical array standing wave acoustic tweezer sound field distribution and wave node movement are simulated using COMSOL software,and experiments to manipulate the axial movement of the target are conducted,which are consistent with the simulation results,and the relationship between sound pressure and levitation capability is explored using the experiments.Then,the principle of potential well generation under symmetric anti-phase superposition effect is analyzed,and the effect of parameters such as the number of array elements on the formation of acoustic traps is analyzed by constructing unilateral phased-array traveling-wave acoustic tweezers using COMSOL.The three-dimensional Twin acoustic tweezer and Vortex acoustic tweezer models were constructed to realize the holographic movement of the acoustic traps,and the correctness of the models was verified against the models in other papers.Finally,the velocity change and position distribution of particles in the acoustic field under the acoustic radiation force were simulated.The droplet kinetic behavior observation experiments were conducted using standing wave acoustic tweezers to observe and record the droplet deformation,cavitation,and oscillation under acoustic manipulation,analyze the causes of their generation,and the sound radiation pressure on the droplet surface under standing wave acoustic tweezers is also simulated using COMSOL.