Manipulation Of Acoustic Waves And Trapping Of Microparticles By Artificial Structures

Sonic crystals(SCs) have received a large number of attentions in recent decade for their ability to manipulate acoustic waves/elastic waves. In recent years, the acoustic surface wave artificial structure and subwavelength acoustic metamaterials also become gradually the research focus. With the deepening study, many novel acoustic applications have been reported by utilizing the SCs and acoustic metamaterials. More recently, the emphasis of acoustic research has focused on acoustic radiation forces(ARFs). As is well known, acoustic waves can produce ARFs as a result of momentum exchange between the object and the incident field when impinging on objects. In this dissertation, we mainly designing three kinds of novel acoustic functional devices and investigate acoustic radiation forces tailored by acoustic artificial structures by using Multiple Scattering Theory(MST) and Finite Elements Method(FEM) to conduct numerical simulations.The main works involved in this dissertation are as follows:Firstly, in the second chapter, an acoustic waveguide based on the omnidirectional reflection of one-dimensional SC is designed to realize the flexible guiding of sound waves. Numerical simulations indicate that high efficiency transmission can be achieved at arbitrary bending angle and over a wide frequency range. Moreover, more flexible waveguide branches can also be easily constructed by introducing more crystal structures into the waveguides.Secondly, in the third chapter, based on localized modes of two-dimensional SC with defects, a multi-directional frequency selector of acoustic wave is proposed by appropriately combining a number of resonant cavities of different size together. The resonant frequency can be changed by varying the cavity size. Hence, with appropriately designing, when a point source is placed in the center of the frequency selector, acoustic waves of different frequency can be driven to radiate out through corresponding port.Next, in the fourth chapter, we present a graded negative birefraction lens by a two-dimensional graded SC with the overlapping bands. The graded negative birefraction is achieved by gradual modification of the lattice spacing along the transverse direction of the lens. We demonstrate that the lens can realize the dual-focusing of parallel incident acoustic waves, and the two focal lengths can be precisely controlled by tuning the thickness and/or width of the lens.Finally, in the fifth chapter, we investigated the acoustic radiation force(ARF)acting on a cylindrical brass particle near an acoustically soft plate patterned with a periodic deep grating. The existence of a negative ARF by which the particle can be pulled towards the sound source is confirmed. In addition, the bandwidth for negativeARF in this soft-plate system is found to be considerably broader than in the stiff-plate systems typically used in previous studies. It is further demonstrated by field distribution analysis that the negative ARF is caused by the gradient force induced by the gradient vortex velocity field near the surface, which stems from the collective resonance excitation of the antisymmetric coupling of Scholte surface waves in the thin plate. The effects of particle location and size on the ARF were also investigated in detail. The negative ARF has potential use in applications requiring particle manipulation using acoustic waves.