Research On Defect State Characteristics And Vibration Energy Harvesting Of Two-Dimensional Magneto-Elastic Phononic Crystals

Phononic crystal is a new type of artificial composite material formed by periodic arrangement of materials or structures.Its unique elastic wave band gap and defect state characteristics have important application values in the fields of vibration reduction and noise reduction,focused imaging,and ultrasound medical treatment.Magnetostrictive materials,as typical smart materials,have a keen and rapid response to external excitations such as magnetic fields.The introduction of magnetostrictive materials into phononic crystals is expected to achieve active control of band gaps and defect states.Therefore,this thesis considers the nonlinear coupling characteristics of magnetostrictive materials,establishes a theoretical framework for coupling the band gap and defect state characteristics of two-dimensional plate-cylindrical and planar magneto-elastic phononic crystals,and develops the finite element quantitative analysis method of its elastic wave "local" propagation behavior control characteristics;and the introduction of piezoelectric materials to form a magneto-elastic phononic crystal energy harvesting system,revealing the influence of magnetic field,pres-tress and temperature on voltage and power.The main research content includes:(1)Considering the nonlinear magnetic-mechanical coupling constitutive characteristics of three-dimensional magnetostrictive materials,a quantitative simulation model of the band gap and defect state characteristics of the plate-cylindrical magneto-elastic phononic crystal with defects is established,the transmission characteristics of band gaps,point defects and linear defect states in the band structure and transmission spectrum under the action of magnetic-mechanical coupling are studied,and the regulation laws of external loads such as magnetic field and pre-stress on the characteristics of band gap and defect states are analyzed.The data results show that the magnetic field and pre-stress have obvious effects on the band gap and defect zone.In the plate-pillar phononic crystal structure with point defects,there are wave localization characteristics and amplification effects at the defect frequency.In the plate-pillar phononic crystal with line defects,the internal waves at the defect frequency have directional transmission characteristics.(2)The characteristics of a vibration energy harvesting system composed of phononic crystals with point defects and piezoelectric materials are studied.First,the band gap characteristics of the unit cell structure are discussed,a finite element model of a two-dimensional unit cell magneto-elastic plate-cylindrical phononic crystal is established,and the effects of longitudinal applied magnetic field,pre-stress and temperature effects,as well as the geometrical parameters of the cylinders on the band gap of the unit cell structure are discussed.Based on the above research,the band gap characteristics of the supercell structure are analyzed,and the influence of magnetic field and temperature on the performance of the vibration energy harvesting system at point defects is revealed.The research results show that the magnetic field,pre-stress and temperature all have an influence on the generation and closure of the band gap.The geometric parameters of the cylinder have a significant impact on the structural band gap,and changing the radius and height of the cylinder can significantly change the band gap width.The magnetic field and temperature have a significant effect on the output voltage and power,as well as the optimal resistance.(3)On the basis of the previous study on the line defect mode,based on the nonlinear magnetic-mechanical coupling constitutive theory,a two-dimensional planar magneto-elastic phononic crystal model is established,and the band gap and waveguide characteristics of the phononic crystal are studied.Two different linear defect modes are considered,one is the traditional linear defect structure and other is the nontraditional linear defect structure composed of a single point defect.The displacement field distribution diagrams of the two linear defect modes are compared,and the wave propagation laws in the two linear defect modes are discussed.Furthermore,the transmission characteristics of two bendable linear defect modes under external excitation are analyzed.The research results show that the line defect mode composed of continuous single point defects is more promising than the traditional line defect mode to become an effective,well-constrained and guided mode.This research not only considers the structure of the line defect of the traditional mode,but also combines the characteristics of the point defect with the transmission characteristics of the line defect,and provides a new design idea for the research and design of wave orientation devices and filters.