Manipulation Of Acoustic Waves By Defected Surface Phononic Crystals

Phononic crystals attract people's attention for their rich physics.Because of the rich and adjustable dispersion relationships,acoustic waves in phononic crystals behave various unique spreading ways.In this dissertation,we research on the control of the spoof surface acoustic waves in surface phononic crystals.As we all know,the spoof the surface acoustic waves as a new type of surface wave have been concerned widely in recent years.The spoof surface acoustic waves have the characteristics of the surface wave but also have its own advantages.Many of properties of the surface waves can be obtained by measuring and analyzing the spoof surface acoustic waves instead.The study of the spoof surface acoustic waves is to provide some guidelines for design various multifunctional acoustic devices.The main work is included as follows:Firstly,the dispersion relation of the spoof surface acoustic wave is influenced by the geometrical parameters,and it is found that the wider and deeper grooves are preferred to realize highly confined surface acoustic waves.We designed a three-dimensional rigid plate with an array of drilled holes.A wide and flat equi-frequency contour of the spoof surface acoustic waves is found.The self-collimation effect was realized due to the unique shape of equi-frequency contour.The conclusion of this study is to provide some theoretical guidance for the design of new acoustic devices.Then we demonstrated that a 90°-bended imaging of spoof surface acoustic waves with subwavelength resolution of 0.316? can be realized by a 45° prism-shaped surface phononic crystal(SPC),which is composed of borehole arrays with square lattice in a rigid plate.Furthermore,by combining two identical prism-shaped phononic crystal to form an interface(to form a line-defect),the excited spoof surface acoustic waves can be split into bended and transmitted parts.The power ratio between the bended and transmitted surface waves can be tuned arbitrarily by adjusting the defect size.Sharp bending scheme and splitting scheme break through the intrinsic inability of self-collimation and realized bend and redirect waves.We believe this research will find applications in various multifunctional acoustic solutions integrated by different phononic crystals devices.Finally,point defects and line defects can be introduced by changing the geometrical parameters of single groove in the core center or one row of grooves.Furthermore,combining the finite element method and the supercell method,it is very convenient to calculate the band structure of point defects and line defects,and obtain the eigen-pressure field of spoof surface acoustic waves which localized in the point defects and the line defects with specific frequency.And the acoustic waveguides in the surface phononic crystal can be realized by using the frequency of defect state.Furthermore,we extend the transport of the spoof surface acoustic waves to three-dimensional space.