Research Of Acoustic Streaming In Ultrasonic Micro And Nano Manipulation Technology

The ultrasonic micro and nano manipulation technology utilizes physical effects of ultrasound like acoustic radiation force and acoustic streaming,and it can be used for trapping,rotating,concentration,and releasing of micro and nano samples.Compared with other types of micro and nano manipulation methods,the ultrasonic micro and nano manipulation method has merits such as less selectivity to manipulated objects,less damage to biological samples,more diverse manipulation ways,and lower-cost devices.Due to incompletion of previous research and low efficiency of finite element simulation,in-depth research on acoustic streaming in the ultrasonic micro and nano manipulation technology need to be implemented.Major contents and achievements are as follows:1.Based on the fundamental theory of acoustics and existing acoustic streaming theory,the detailed expression of the time-averaged second order pressure is derived,which is one of the driving forces in the acoustic streaming field.Using the sound and fluid field modules in the finite element method(FEM)software COMSOL Multiphysics,the improved acoustic streaming simulation method is established.2.Characteristics of the steady acoustic streaming field generated in a two-dimensional rectangular chamber with a traveling wave have been clarified.The acoustic streaming distribution in the chamber is simulated by using the improved acoustic streaming theory.Compared with the analytical solution of acoustic streaming field,the correctness of the improved acoustic streaming theory is verified.The changing laws of the acoustic streaming with vibration conditions including frequency and length of the vibration source,distance and initial phase difference between two vibration sources are obtained.The influence of particle existence in the chamber and temperature change of the medium on acoustic streaming is clarified by further FEM calculation.3.Characteristics of the steady acoustic streaming for micro/nano particle concentration near the needle of an ultrasonic needle-droplet-substrate system have been clarified.The acoustic streaming field on the substrate and the influence of structural parameters on acoustic streaming is simulated by the FEM.The working principle of the system is well explained by the calculation results.The parameter dependency of the distance between the needle and substrate,the needle's radius,the droplet's height and radius,and the shape of the needle's cross section on micro/nano particle concentration capability is also clarified.The influence laws of the acoustic streaming on theconcentration characteristics of micro/nano particles can be used for the optimization of the ultrasonic needle-droplet-substrate system.4.The generation condition and characteristics of the spiral vortex field for nano particle concentration in the droplet of an ultrasonic needle-droplet-substrate system have been clarified.The spiral vortex field on the substrate is analyzed by experiment and theory.The experimental and FEM results show that the concentration spot number,which is related to the spiral vortex number,can be changed by the vibration distribution of the ultrasonic needle immersed in the droplet.It is also found that the spiral vortex velocity decreases as the distance decreases from the vortex center,which is beneficial to the stability of nano particle concentration.In addition,according to the kinetic analysis of particles in the spiral vortex field,the necessary and sufficient conditions to concentrate nano particles are obtained.5.The generation condition and characteristics of the acoustic streaming field for a single nanowire trapping in the droplet of an ultrasonic nano tweezers system have been clarified.The acoustic streaming field around the micro manipulation probe(MMP)and the influence of structural parameters on acoustic streaming is simulated by the FEM.The working principle of the system is well explained by the calculation results.The parameter dependency of the distance between the MMP and substrate,the MMP's radius and length,and the droplet's height on nanowire trapping capability is also clarified.The influence laws of acoustic streaming on the nanowire trapping characteristics can be used for optimization of the ultrasonic nano tweezers.6.The calculation method of acoustic streaming excited by multiple vibration sources working at different frequencies has been obtained by theoretical derivation.The acoustic streaming field excited by multiple vibration sources in a heptagonal chamber is simulated,and the simulation results are verified by the experiment.The FEM calculation results show that comparing with single-frequency acoustic streaming,multi-frequency acoustic streaming is more complex.The distribution of multi-frequency acoustic streaming field depends on the vibration sources' positions,number,frequencies,and amplitudes.The calculation results reveal a diversity of multi-frequency acoustic streaming,which can provide another new method of expanding ultrasonic micro and nano manipulation function.