Active Control On Elastic Wave Metamaterials As The Plate Type With Defects:Point And Line Defects,Switched Waveguide And Topological Immune

In recent years,the studies on phononic crystals and elastic wave metamaterials have received a lot of interests.Phononic crystals and elastic wave metamaterials are the composite structures in which the elastic material parameters and other constants change periodically.These periodic systems can show band gaps in which the propagation of elastic wave is forbidden.On the other hand,it can propagate freely beyond the band gaps,another important characteristic of phononic crystals is defect state.If there are some defects in the phononic crystals,the elastic wave will be located near the defect or propagate along the defect.Nowadays the active control of phononic crystals and elastic wave metamaterials has received more and more attention.One valuable research subject is applying the piezoelectric shunting circuits to adjust the characteristics of band gaps.The underlying mechanism is that the intrinsic parameters of piezoelectric patches can be changed by connecting shunt circuits.On the other hand,the research about the topology has gradually become a hot topic in physics and acoustics in recent years.Many scientists have demonstrated the topological immune and phase reconstruction for two dimensional phononic crystals.According to the topological characteristics in the acoustics,we can extend the discussion that whether the topological immune of the flexural wave can be found for the elastic wave metamaterials as the plate type.So both the numerical simulation and experiments are performed and this work is focused on the influences of the shunting circuits on band gaps,the active control of the point and line defects,switching waveguide and topological immunity.This work is mainly concerted on the propagation of the flexural wave in the plate model.At first,the regulating effect of the external electric circuits in the plate attached with piezoelectric shunting circuits is discussed.After that,the point and line defects can be formed by changing the parameters of some circuits.Then the energy concentration by the point defect and wave guide by the straight line defects are discussed.It mainly depends on adjusting the parameters of inductance,capacitance and resistance to change structural band gap or generate the point and line defects.Then,the band gap characteristics,wave energy concentration,straight wave guide are analyzed.In this section,it is proved that the piezoelectric shunting circuits can effectively tune the band gap,introduce the point defect and the corresponding energy concentration,as well as the straight wave guideSecondly,the active control of the flexural waves in switchable waveguide is studied.Previous waveguides can only concentrate the energy of elastic waves and show the propagation of elastic waves only along a single direction.As a comparison,the switchable wave guides are connected by the piezoelectric patches and attached by the negative capacitance circuits to control the material parameters.And the active control on the propagation direction of the flexural wave is achieved.Furthermore,the experimental model is made by the 3D printing technology and connected by the piezoelectric shunting circuits with negative capacitance to performed the experiment and the active control of the flexural wave is presented.Finally,the topology concept in the physics and acoustics is introduced into the elastic wave material plate,which can show the topological property of the flexural wave.The elastic wave metamaterial plate consists of the hexagonal array which is connected with the piezoelectric shunting circuits.The Dirac cone is found by adjusting the size of the unit cell.Based on these designs,the numerical simulations and discussions are illustrated to show the topological immune.Then the Dirac cone is broken and the new Dirac point can be generated by the connecting negative capacitance circuits.These investigations can demonstrate the topological immune can be achieved for the flexural wave in elastic wave metamaterial plate.