The Study On Properties Of Lamb Waves Phononic Crystal Anti-symmetric Boundary And Heterostructures Interface

After 20 years of development, phononic crystals, the periodic composite materials or structures own the elastic wave band gap, has received increasing attention. Its rich physical characteristics and extensive application prospect are inseparable. The most significant physical property is the existence of phononic band gap, namely, the elastic wave, which in frequency range of band gap, can’t propagate in this phononic crystal. Due to this characteristic, phononic crystal can be design into many novel acoustic devices, there is great potential in vibration isolation and noise reduction. Early days, People mainly investigated bulk waves in phononic crystals. Recently, people have been extended their study from bulk waves to Lamb waves. In this paper, phononic crystal as to be the research object, we will study on the propagation performance of Lamb waves by the finite element method. This paper mainly includes the following contents:In chapter one, the concept and basic features of phononic crystals was introduced, and we summarized the research status of phononic crystals. Meanwhile, the research contents and the latest developments of Lamb waves in phononic crystals and the schoch effect of acoustic metamaterials has carried on the more detailed introduction, respectively. Finally, the study of this paper has a simple introduction.In chapter two, in view of the structure of boundary layers, we propose phononic crystals with the anti-symmetric boundary structures. Using the finite element method, we theoretically and numerically investigate the band structures of the anti-symmetric boundary phononic crystal. Numerical results show that there are three band gaps in the frequency region below 4 MHz in the band structure. And the Lamb wave band structures are all in good agreement with the transmission power spectra. The band structure of the anti-symmetric boundary phononic crystal is significantly different from those presented in the papers available. We also found that there exists an essential distinction in the formation of the band gap between the anti-symmetric and the symmetric boundary model. The effects of the anti-symmetric boundary on the intrinsic properties of eigenmode are different from those of symmetric boundary.Further investigations tell us that the thickness of the boundary layers can remarkably change the width and the location of the band gaps. On the other hand, the variation of the width of the band gaps with the evolution of the system from the symmetric boundary model to the anti-symmetric boundary model has been studied. The investigation shows that the band gaps can be opened and closed on some special condition. The band gaps are sensitive to the degree of stagger of the two boundary layers, and different band gap shows a different response to the profile of the boundary. In other words, the topological distribution of the boundary layer has an influence on the band structures.In chapter three, using the same research method, we investigated the interface guided mode of Lamb waves in two-dimensional phononic crystal heterostructures. The results show that the interface guided modes can be obtained by lateral lattice slipping or by the interface longitudinal gliding. The number of the interface guided mode mainly depends on the lateral slipping separation or longitudinal gliding separation. Significantly, it is observed that the condition to generate the interface guided modes of Lamb wave is more demanding than that of the studied fluid-fluid system. The interface guided modes are strongly affected not only by the relative movement of the two semi-infinite PCs but also by the thickness of the PC plate.In chapter four, we give the main conclusions of this paper.