Study On Adjustable Band-gaps Of Phononic Crystal

In the past decade, the band-gap structure of phononic crystal has received a great deal of attention.Phononic crystal is made with different elastic properties of periodic composite materials.In the band-gap structure the phenomenon of forbidden band gaps can be observed.Located in the forbidden band gaps the propagation of elastic waves are forbidden.According to the characteristics of the phononic crystal,it can be applied to the vibration and noise reduction, new acoustic devices and other fields of engineering applications.Another motivation of the research is the rich physical phenomena such as Anderson localization observed in the study of phononic crystal.Because the Lamb waves have potential application to non-contact and non-destructive evaluation and characterization of sheet materials in industry, more and more attention is paid to propagation of Lamb waves in periodic composite systems.In addition, there has been a growing interest in using Lamb waves for a variety of physical, chemical, and biological sensors. The changes of physical, chemical, or biological etc. conditions on boundaries lead to the change of propagation velocity of lamb waves. The small change of mass, stress and viscosity etc. can be induced by the change of propagation velocity. The lamb wave minor sensor has the features of high sensitivity and working in liquids. So it has the potential application to monitoring the physical, chemical, environmental, and biochemical processes. This paper focuses on the band-gaps of propagation of Lamb waves in periodic phononic crystal,quasi-periodic phononic crystal and thickness-modulated one-dimensional periodic phononic crystal.The background of phononic crystal,the main research methods of the band gaps of sonic crystal is introduced in Chapter1.Chapter2briefly introduced the basic theory of the band structure,the basic concept of phononic crystal and the application of the simulation software COMSOL Multiphysics.Based on the plane-wave expansion method (PWE), the equations of the band structure in periodic phononic crystal and quasi-periodic phononic crystal are studied in Chapter3. Two crucial parameters, i.e, the ratio of the plate thickness to the lattice spacing, the generation number of quasi-periodic phononic crystal are discussed in details for the influence of formation of band gaps.The band-gap structures of lower-order Lamb waves in thickness-modulated one-dimensional periodic phononic crystal are studied in Chapter4,which is based on the plane-wave expansion method(PWE).The transmitted power spectra for thickness-modulated one-dimensional periodic phononic crystal was calculated by using COMSOL Multiphysics,which was in good agreement with the results by the transfer matrix method(TM).Chapter5introduced the pipeline phononic crystal.And the band structures of pipeline phononic crystal were studied.Finally, the main conclusions of this thesis are drawn in Chapter6.The main contribution of this work lies in three aspects:1.The band-gap structures of Lamb waves in periodic composite material thin plates are studied by using the plane-wave expansion method(PWE),the transfer matrix method(TM) and COMSOL Multiphysics respectively.The existence of band gaps for low-order Lamb wave modes in composite thin plate is demonstrated.2.The band-gap structures of Lamb waves in one-dimensional quasi-periodic phononic crystal are studied. It is found that, compared with the band-gap structure of periodic sonic crystal, the quasi-periodic model exhibits critical different behaviors in the band gaps structures.The different ratio of the plate thickness to the lattice spacing, the change of the generation number of quasi-periodic phononic crystal will affect the band-gaps of the quasi-periodic models.3.When the thickness of one-dimensional phononic is modulated periodically, we find that the original energy band splits into many sub-bands.The band structure of low-order Lamb waves in thickness-modulated one-dimensional periodic phononic crystal will change with different modulation parameter and different intension of modulating.