The Characteristics And Tunability Of Wave Band Gaps In One Dimensional Magneto-Electric-Elastic Phononic Crystal

Phononic crystal is a new type of functional material composed by two or more elastic materials arranged in a periodical sequene. Due to its frequency stop-bands (band gaps) where the propagation and vibration are forbidden for all elastic wave vectors, phononic crystals have numerous potential engineering applications such as sound isolation, vibration isolation and sound filter. The study of sonic crystals containing piezoelectric or piezomagnetic materials have received widespread attention, and been extensively applied in acoustic wave devices, electromagnetic surveying, transducer and many other fields. As a new type of highly strategic smart materials in the twenty-first century, giant magnetostrictive materials have little application in the study of phononic crystals. In this thesis, the longitudinal wave band gap characteristics of phononic crystal containing with magnetostrictive material are studied systematically; as the SH wave propagates in the laminated magneto-electro-elastic phononic crystal, the dispersive relations for the imperfect and perfect interface are given. The primary obtained results are as followsFirstly, tunability for controlling and adjusting the longitudinal wave band gap characteristics of epoxy/Terfenol-D and Ni6/Terfenol-D rod-shaped phononic crystals are theoretically investigated with considering the magneto-mechanical coupling; Z-L model is adopted to describe the constitutive relations of magnetostrictive material; according to the Bloch theorem and periodicity of structure, the generalized eigenvalue equation can be obtained by the plane wave expansion method. The numerical results indicate that the edge of each band gap first decreases, then increases and finally levels off with the increasing external static magnetic field; as the compressive pre-stress rises, the widths of longitudinal wave band gaps of the epoxy/Terfenol-D phononic crystal increase first and finally keep to be a constant, but the widths of longitudinal wave band gaps for Ni6/Terfenol-D periodic composite have a progressive decline trend and finally level off; there will respectively appear one, two, three and four maximums for the widths of the first, second, third, and fourth band gap as filling fraction ranges from0to1.Secondly, taking the magneto-electro-mechanical coupling into account, the plane wave expansion method is also used to study the band gap characteristics of phononic crystals constituted of piezoelectric material and magnetostrictive material. The numerical results show that the piezoelectric effects nearly have no influence on the band structures of PVDF/Terfenol-D and PVDF/Ni6phononic crystals,but have remarkable influence on the band structures of PZT-4/Terfenol-D and PZT-4/Ni6phononic crystals; the band gap characteristics can also been effected by the filling fraction of phononic crystal, the piezoelectric constants and elastic constants of piezoelectric materials; with the increase of compressive pre-stress, the curves for edge of band gap of PZT-4/Ni6phononic crystal vs. H obviously move to the left, but the curves for edge of band gap of PZT-4/Terfenol-D phononic crystal vs. H obviously shift towards the right.Finally, the dispersion equations of laminated piezoelectric phononic crystal with imperfect interfaces are derived by using the transfer matrix method and Bloch theorem. In the last chapter, a summary of our works and an outlook for the future works on the investigation of sonic crystals are presented in the fifth chapter.