Investigation Of The Surface Acoustic Wave Properties For 2D W/Si Phononic Crystals

Phononic crystals are composite materials which consists of two or many kinds of materials. Phononic crystals have own the elastic wave band gaps and periodic structures.During acoustic wave propagation, some frequent acoustic wave will be suppressed and formed phononic band gaps. The concept and theory of phononic crystals provide new ideas for surface acoustic wave.As the Science and Technology develops rapidly, traditional materials have far can't satisfy the requirements of human beings. The appearance of the composite materials with special performance alleviate this contradiction. Starting from material parameters(Young's modulus, shear modulus and density) and external environment(temperature), this degree dissertation analyzes which is the main factor affecting the phonon crystals band structure.With plane wave expansion, the thesis calculated the band structure of the 2D W/Si phononic crystals. During the structure function fixing, numerical results show that the width of the band gap increase with increasing the filling fraction, after reaching the peak, then fall to zero. The present works studied how the material parameters effect on the 2D solid/solid phononic crystals, by introducing virtual material. It found that when the shear modulus of the scatter is smaller than the matrix body, the band gap can still appear in the cases of fill rates is very small, and with the increase of filling rate, the band gap is wider and wider, but overall,the phononic crystals band gap formatted very narrow. While the scatter shear modulus is greater than the matrix, the phononic crystals appear only in the case of high fill rate, and the band is wide. It is interesting that the density of the scatter plays a opposite role of the phononic crystals band structures. When the scatter density is less than the substrate, the band gap appeared under the condition of the filling rate is very high, while the scatter density is greater than the substrate, even in the case of fill rate is very low, the band structure can also still appear. Compared to the former, it is not quiet obviously that the Young's modulus of the scatter impacts on 2D Solid/Solid phononic crystals. The phononic crystals band gap has never appeared even the Young's modulus of scatter and matrix are 30 orders of magnitude.Above all, it can conclude that the Young's modulus and density play important roles in the band gap of 2D S/S phononic crystals, while the effect of Young's modulus of the phononic crystals is very small.In some degree, both structure function and material parameters decide the band gaps of the phononic crystals. However, it can't be neglected for the influence of the external environment especially temperature. Through analyzing how temperature effect on the related parameters of Silicon, it obtain the effect of temperature to the 2D W/Si phononic crystals.With the temperature increasing, the studies show that the band structure of phononic crystals moves to lower frequency and the width band structure become more and more narrow.Finally, the affect cladding layer of 2D W/Si PCs on the band structure was analyzed with the finite element method. the dissertation analyzed how cladding layer of 2D W/Si PCs affect the band structure. The studies show that the speed of sound in the cladding layer has enormous influence on elastic wave transmission on the surface of 2D W/Si PCs. When the sound velocity of the cladding layer is greater than that of the substrate, the incentive which is loaded on the surface of the PCs dissipate in cladding layer, while the acoustic velocity of the cladding layer is smaller than the substrate, the acoustic wave spreading on the surface of the PCs has a very good performance.