Study On The Band Gaps Tunable Method Of Two-dimensional Phononic Crystals Based On Material Properties Of Shape Memory Alloys

In recent years,people have made some achievements in the research of PCs in terms of vibration and noise reduction,acoustic component design and so on.But because the structure and material are fixed,the band gap of the PCs is also determined.In order to make the band gap frequency meet the frequency requirements of different use environments,more and more researchers are beginning to explore the adjustable band gap.At present,there are still shortcomings such as inconvenient tunable operation and discontinuous tunable.In this article based on the SMA material parameters(Young's modulus)and the characteristics that the shape can change before and after phase transformation,two-dimensional solid/fluid patterns and two-dimensional plate-like PCs are designed respectively,through the method of combining numerical calculation,finite element analysis and experimental testing,the effect of SMA material characteristics on the band gap regulation is studied,and the band gap tunable model based on the change of SMA Young's modulus and shape change are established respectively.It also explores the application of defect mode properties in tunable waveguides by creating defects using adjustments in the parameters of the tuning model itself.The main research content is as follows:(1)Based on the influence of SMA Young's modulus change on band gap adjustment,a tunable two-dimensional solid/fluid type PCs is designed.First,the effect of fill rate on band gap regulation is studied,and the model structure with the widest regulation range is determined.Second,the effect of viscous changes in water in different temperatures on the structure of PCs can be discussed.Finally,due to the Young's modulus of SMA the gradual characteristic cannot be applied in engineering,the idea of combining the change of Young's modulus with changing the orientation of the scatterer is proposed,and a double tunable method is established to realize a large-scale and continuous tunable of the band gap.A reference is provided for the design of the combination of multiple regulation methods as well.(2)Based on the characteristics of the shape change of SMA,the adjustable two-dimensional plate PCs is designed.The relationship between the model structures,the dispersion relationship and the wave field distribution are analyzed,and the adjustment of the band gap by parameters such as the inner radius of the column,the height of the column and the curvature of the SMA in the model are studied.By changing the size of the parts in the model or the curvature of the SMA,the different band gaps can be adjusted separately.(3)Based on the double tunable method,the tunable line defect waveguide and the tunable coupled-resonator acoustic waveguide are designed by selectively changing the Young's modulus and the orientation of the scatterer,and the transmission characteristics and transmission frequency tunability of the waveguide are studied.By combining the supercell method and the finite element method,the defect mode characteristics of the model is studied,the transmission frequency tunable range of the linear defect waveguide is obtained,and the bending transmission and demultiplexing of energy are realized.However,it is found that it has the disadvantages of high energy transmission loss and easy interference of guided modes.Furthermore,a coupled-resonantor waveguide is designed through a double tunable method.Based on the linear chain theory of coupled resonators,the influence of the distance between adjacent resonators on the dispersion relationship is discussed.By constructing waveguide paths with different lengths and number of bendings,the influence of path length and the number of bends on the energy transmission characteristics is studied.The results show that the coupled-resonantor waveguide based on the double tunable method can realize the improvement of energy transmission,and has the characteristics of flexible path design,not affected by the length and number of bends,and continuous wide-range tunable.In addition,it is found in the research that the waveguide transmission frequency is related to the ratio of the Young's modulus of the intact and the defect PCs,and the idea of continuous tunable of the transmission frequency by adjusting the ratio of the Young's modulus is proposed.(4)Based on the tunable method of shape change,the tunable waveguide model is designed by selectively changing the curvature of SMA.The supercell method is combined with the finite element method to study the transmission characteristics and transmission frequency tunability of the waveguide.The results show that by changing the shape of the SMA,the defect construction,the flexible design of the waveguide path and the adjustment of the transmission frequency can be achieved.Finally,through the design of experiments,the feasibility of the tunable method is proved,and it can be expected to be used in practical engineering applications.