Dimensional Phononic Crystals With Wide Band Gap And Defect States

Phononic crystal(PC) is a new concept which has been brought forward based on the research of electron's movement in crystal lattice and optical wave propagation in the photonic crystal. PC researching has a fundamental meaning in physics and potential values in application. By the finite domain and time difference method(FDTD), the band characteristics of two-Dimensional solid/liquid PCs with two components, three components and their combined structures have been calculated, and the defect structure also have been involved. There are more details as followed:Firstly, the FDTD method which is usually used in the researching of phonotic crystals has been extended into the study of phononic crystals, and a FDTD method about phononic crystals was deduced in detail, based on the elastic wave theory.Secondly, the band structures and defect states of two-D phononic crystals which consist of solid scatters distributed in liquid base in square array matrix, have been investigated, as well as the influences of certain substance properties of the components, such as material density and elastic constant et al. It is founded that the lowest band gap is closely related with the substance properties of the components and filling ratio of the inserted rods in unit cell, a bigger elastic parameterλ, of liquid base and a bigger ratio of density of scattering rods to that of liquid base will introduce a wide lowest frequency band gap, and also, the defect in the periodic structure of phononic crystals will bring out some defect states or bands which are affected by the defect size, position and the substance properties, and these defect states are usual restrictedly located in the site of the defect rods.Thirdly, the three components structure, with the example of rubber/steel/water system, has been analysed. Results show that the rubber/steel/water system, compared with the steel/water two components system, is easy to get a wider band gap, which is affected by the thickness of the soft coated layer, the filling ratio of the coated cyliner and the width of the defect line, a bigger coated layer and filling ratio will reach a wider band gap, and a wider defect line will also result in a bigger defect band in the bang gap of the perfect structure.Finally, the combined structure of steel/water and rubber/steel/water has been researched. It is gratifying that a combined band gap with the band gaps characteristics of the defect structer of steel/water and rubber/steel/water respectively has been founded. So, the combined structure have not only a lower frequency gap, but also a higher frequency gap and the defect state in the higher frequency gap.