Studies On The Bandgap Properties Of Two-dimensional Quasi-Periodic Phononic Crystal Plates

Phononic crystal(PNC)generally refers to artificial periodic structures and functional material with acoustic band gaps.The essential property of the PNC is its band gaps.At present,the research of the two-dimensional quasi-periodic phononic crystal band gap characteristics and lamb wave in one-dimensional quasi-periodic phononic crystal board band gap characteristics have get a great progress.But at the moment there is little study for lamb wave in two-dimensional quasi-periodic phononic band gap characteristics of crystal plate.With the emergence of functional materials and smart structures,people can design adjustable band gap of phononic crystal structures by changing the material parameters of the functional materials in electrical,magnetic,thermal fields.In recent years,many scholars began to design and research how to introduce piezoelectric materials and other functional materials into the phononic crystals.And they explored the features and functions of the tunable band gap of the phononic crystal structures.So,in this thesis the band gaps of two-dimensional eight-fold and ten-fold QNPC plates will be studied.By using the finite element software COMSOL Multiphysics,the following problems for lamb wave’s propagation in two-dimensional QPNC plates will be analyzed:1.We researched the band gap characteristics of two-dimensional eight-fold QNPC plates with embedded scatterers.The influences of structural parameters and material parameters on lamb wave’s band gapare studied.The structural parameters include filling rate and the ratio of thickness and the lattice constant(d/a),and the material parametersincludes elastic modulus and density,at the same time,the band gaps of two-dimensional ten-fold QNPC plates with surface pillars are also been discussed.The results show that the influence of the structural parameters on the band structure gaps is more clearly than the material parameters.But,the band gaps width is more stable by changing the material parameters.2.the influences of the structural parameters and the piezoelectric coefficients on the band gaps of the piezoelectric two-dimensional eight-fold QNPC plates with surface pillars are analyzed.The structural parameters includes the height of the piezoelectric pillars and the thickness of the epoxy matrix.The results show that there doesn’t have band gaps in QNPC plates with embedded scatters,and there has obvious band gaps in QNPC plates with surface pillars.The change of structural parameters has an obvious effect in band structures.The defect modes of piezoelectric two-dimensional QNPC plates are also studied in this thesis.The studies show that it is easy to obtain the curved waveguided mode by introducing the quasiperiodicity in the PNCs.