Researches On Controlling Acoustic Fields By Artificial Structures And Particle Manipulation

In recent decades,precise control of micro-and nano-particles,biomolecules and biological cells has become increasingly important in physics and biomedicine,with applications emerging in fields such as target objet trapping and self-assembly,biochemical analysis,cell separation and sorting.Following this demand,contactless particle manipulation technologies have been developing actively,such as electro-kinetics,magnetic tweezers,and optical tweezers.Compared with other manipulation technologies,ultrasonic manipulation,with the advantages of lower power consumption,deeper penetration depth in light opaque media,maintenance of cell viability,versatile and easy integration into microfluidic systems,has shown potential in variety of applications.On the other hand,since its inception,acoustic artificial structure,with the advantages of adjustable structure parameter,has provide a practical and effect method in controlling of acoustic wave propagation and spatial confinement,meanwhile,the localized acoustic near field induced by the interaction of acoustic wave and artificial structure has been shown to be able to trap small particles efficiently,with lower acoustic intensity than conventional acoustic tweezers.Based on this,we perform particle manipulation assisted by phononic crystal plate in this article.By designing the artificial structure to construct special acoustic field,and then to analyze the acoustic radiation force and acoustic radiation torque on particles in the induced acoustic near field.The main works are listed below:1.Construction of one and two dimensional acoustic potential wells assisted by phononic crystal plate and realizing multi-particle trapping and patterningBased on the resonant transmission properties of phononic crystal plate,we design and fabricate the metal plate with one dimensional,two dimensional and quasi periodic structure.One and two dimensional acoustic potential wells were constructed through the interaction of acoustic wave and artificial structure plate.By analyzing the acoustic radiation force on particles placed in the acoustic field,we found that the forces on particles will always points to the position of the localized acoustic field(eg.the positions of slit and hole).Through experiments,we observed a number of polystyrene particles with different sizes can be easily trapped and patterned in one and two dimensional,for example,linear,square,triangular,or quasi-periodic arrays,depending on the structures of the phononic crystal plates.2.Construction of an adjustable acoustic field assisted by phononic crystalplate and realizing particle's selective trappingBased on local resonant mode of acoustic materials,we design a phononic crystal plate with compound period,which consists of a thin brass plate with periodic slits alternately embedded with two kinds of elastic inclusions,polyethylene and epoxy.We present that the acoustic system can construct adjustable acoustic field and achieve particle's selective trapping.Because of the different resonant frequencies of the two elastic inclusions,the acoustic field could be controlled via the working frequency.Particles can be trapped and transported between adjacent traps under the influence of the adjustable acoustic field.3.Generation of first-order acoustic vortex beam assisted by artificialstructure and realizing particle manipulation.Converting acoustic plane wave to the first order acoustic vortex beam was realized assisted by an artificial structure plate,which is brass plate with Archimedean spiral grating engraved on its back surface.The typical intensity and phase patterns both in simulation and experiment demonstrate the formation of the first order acoustic vortex beam.On the one hand,we experimentally realized annular patterning of polystyrene particles with diameter of 90um in the action of this acoustic vortex field.On the other hand,we realized a PLA disk self-rotating in water in the generated acoustic vortex beam.Acoustic orbital angular momentum transfer to an acoustic absorptive matter is demonstrated.The ratio of acoustic radiation torque and absorbed energy is also demonstrated through our experiment.4.Generation of acoustic vortices assisted by a dual focused coherent Gaussian beams and particle manipulation.We analyzed the characteristics of acoustic field distribution generated by a pair of coherent acoustic Gaussian beams in coaxial and non-coaxial case.The numerical results show that,in the case of coaxial,the resulting interference field is acoustic standing wave field.However,in the case of non-coaxial,one dimensional acoustic vortices are formed by the interference between the two non-coaxial coherent acoustic Gaussian beams.Besides,we carried on the researches of acoustic radiation force and radiation torque on particles by using the resulting acoustic standing wave field and vortex field.