| Summary: | 碩士 === 國立成功大學 === 機械工程學系 === 104 === The present study propose using the numerical technique, which names synthesis of spatially variant lattice, to spatially vary the orientation of the unit cell, lattice spacing, filling ratio and other properties of a periodic structure throughout its volume in a way that leaves the overall lattice smooth, continuous, defect-free and minimal deformation. Based on keeping the geometry of the unit cells in a spatially variant lattice consistent with that of a uniform lattice, the ability to spatially vary the orientation of the unit cells throughout a lattice enables directional phenomena like band gaps, anisotropy and dispersion to be fully exploited to control the waves. Considering two-dimensional square lattice phononic crystals with two kinds of elastic inclusions (rectangular and circular inclusions) immersed in fluid, the plane wave expansion method is used to obtain the band structures and equi-frequency contours of the phononic crystals. And, the finite element commercial software is employed to simulate the acoustic pressure field in the structures. As a result, using spatially variant lattice to spatially vary self-collimation of the two-dimensional phononic crystals of rectangular inclusions can manipulate the self-collimation beam with abrupt bends. Besides, using spatially variant lattice to spatially vary the effective refractive index of the two-dimension phononic crystals of circular inclusions can realize the acoustic bending waveguide and acoustic black hole.
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