Acoustic Tamm States And Cavity Resonant States Of One-dimensional Multilayer Structure Phononic Crystals

In recent decades, the material of the defect states has become a hot topic research scholars, defects of phononic crystals break the periodic structure of the crystal, so that the transmission characteristics of elastic wave appear abnormal phenomenon, the study of phononic crystal has a wealth of physical significance, at the same time, on the development of sound functional materials also have practical application significance,for example: The new filters and soundproofing materials etal.. This is because the occurrence of locally resonant in defects of defect states phononic crystals, thus affecting the acoustic interaction between the layers of the medium, changing propagation mode of the wave, and then change the acoustic properties of the material. There are many research reports about electromagnetic wave as the classical wave in the defect states of photonic crystals, but study of the phononic crystal defect states are not many, and the main also confined to the surface states of phononic crystal, this paper mainly studies that localized state is formed on defects inside phononic crystal.The paper use the transfer matrix method to calculating the propagation of acoustic waves in one-dimensional phononic crystals with defects. Presence of its defect states dramatically changed the acoustic properties of the system, the system will produce anomalous transmission in the band gap region, the transmitting rate of the system is great related to not only the component medium arrangement and number of layers, but also to the thickness of the medium is also relevant, at the same time according the displacement field distribution of anomalous transmission, the localized state is divided into two modes, and a detailed analysis of the similarities and differences between the two modes. The main innovation of this paper are as follows:Firstly, construct a one-dimensional multilayer structures composed of a thin defect layer sandwiched by two phononic crystals(PCs), study the propagation properties of acoustic waves in the structures. Defect states produced by the thin defect layer is called Tamm states, two kinds of acoustic Tamm states(ATSs) will appear due to the different contrasts of acoustic impedances between the defect layer and its neighbor layers. Both of these two typical ATSs can result in transmission peaks in band gaps, but having very different field distributions. According to the analysis of phase properties, the frequency of transmission peaks can be exactly determined by the resonant phase condition. Due to strong resonances resulted by ATSs, its field strength at the resonant frequency will be greatly strengthened, a nearly complete absorption can be achieved in the system with only a small absorption coefficient. The magnitudes of both transmission and absorption peaks are greatly dependent on the periods of the PCs.Secondly, on the basis of the above structure, increasing the thickness of the defect layer, so that it and the thickness of the surrounding medium in the same magnitude, it will produce another locally resonant states: cavity resonance states. We also according to the displacement field and phase change to analyze the cavity resonance states, with ATSs compare, analyze characteristics of cavity resonance states' s displacement field distributions and phase change. With defect layer width increases, the local resonance states gradually change from ATSs to cavity resonance states.