Controlling Acoustic Fields By Two Dimensional Artificial Structures And Matter Manipulation

In recent years,the acoustic artificial structure has aroused much interest among the researchers,because of its rich physics and broad applications.By utilizing the artificial structure,researchers can realize many interesting phenomena,such as acoustic topological transport,negative effective mass densities,extraordinary transmission,and so on.The artificial structure has been widely used to control the propagation of acoustic wave and obtain special acoustic fields.Besides,the transfer of momentum between the acoustic wave and matter will result in the mechanical effect which can be used to manipulate objects.Therefore,it has become a research hotspot of realizing a diversified acoustic manipulation by using special acoustic field.In this thesis,we will demonstrate the acoustic controlling based on the two dimensional annular acoustic metamaterials and acoustic artificial structure plates,and realizing the frequency selective trapping and rotational manipulation based on the artificial structure plates.The main works are listed below:1.Realization of acoustic omnidirectional radiation with the acoustic metamaterialsAcoustic metamaterials are artificial structures with unique properties that offer great flexibility for manipulating acoustic waves.Based on the Fabry-Pérot resonant of space-coiling structure,we describe the design and fabrication of a two-dimensional annular anisotropic metamaterial with an azimuthal effective density approaching zero and demonstrate its robust omnidirectional radiation performance.Locating two sources at a distance from one another or placing a cross-shape obstacle between them inside the cavity of the metamaterial produces acoustic omnidirectional radiation over a wide frequency range.This is quite different from the behavior in the cavity mode.Such anisotropic zero-density metamaterial can be considered as a source shifter,which may have applications in acoustic manipulation,acoustic communication,cloaking,and sonar systems.2.Rigorous Analytical Model for Multipole Emission Enhancement Using Acoustic MetamaterialsWe present a rigorous analytical model for understanding the multipole emission enhancement of sound using acoustic metamaterials.A two-dimensional cylindrical hyperlens-like structure is utilized as a demonstration structure.An analytical expression for the enhanced efficiency is obtained via radiation impedance theory.The analytical results show that enhanced multipole radiation can be achieved by using only one monopole source encircled by the structure.The good agreement between the analytical and the simulation results and the experimental results verifies the applicability of our analytical model.Consequently,our analytical model provides an efficient and intuitive tool for synthesis and analysis of enhanced emission systems.3.Realization of frequency selective manipulation by utilizing a compound phononic crystal plateBased on the research of periodic phononic crystal plate,we design and fabricate a compound phononic crystal plate which consists of big hole-array and small hole-array.The compound phononic crystal plate has two resonant frequencies and the adjustable local acoustic field can be excited by the incident planar wave with different frequencies.Due to the acoustic radiation force resulted from the local field,the polystyrene particle can be trapped into the position of local field and realize the frequency selective manipulation.The feasibility of using compound phononic crystal plate to realize frequency selective manipulation is verified by experiments.4.Rotational manipulation by acoustic radiation torque of high-order vortex beamsWe propose an effective way to generate high-order acoustic vortex beams simply by a structured plate and demonstrate flexible rotational manipulations on objects with different shapes such as disks or small balls or sticks by the generated vortex beams.Two structural plates carved with one set or two sets of Archimedeanspiral gratings on a single side are fabricated to get the first-order and second-order acoustic vortex beams at the same frequency,respectively,acoustic radiation torque of which is experimentally analyzed through the rotational manipulation of a standard acoustic absorption disk.Furthermore,we extend the rotational manipulation on different objects such as small balls and sticks,which gives an intuitive picture of angular momentum transfer from vortex beams to absorption materials.We believe that the present work will pave a way to potential applications in acoustic and biomedical field.