Structure Design And Characteristic Analysis Of Giant Magnetostrictive Actuator For Thermoacoustic Refrigeration

Thermoacoustic refrigerators have been widely used in aerospace,information and other fields because of their simple structure and high efficiency.Using piezoelectric ceramic speakers as the sound driver can effectively reduce the volume of the thermoacoustic refrigerator,but it also has the disadvantage of unstable operation.Using giant magnetostrictive actuators(GMA)to replace piezoelectric ceramic speakers can further improve the output characteristics and effectively increase the input sound power density.However,due to the hysteresis characteristics of giant magnetostrictive materials(GMM),there is a hysteresis phenomenon between the input current and the output displacement of the GMA with GMM as the core component,which seriously damages the stability of the GMA.This paper intends to design a GMA to replace the piezoelectric ceramic speaker as the sound driver of the thermoacoustic refrigerator.The research work completed around the structural stability of the GMA is as follows:(1)GMA structural parameter design for thermoacoustic refrigeration can increase the electromagnetic conversion rate,and can also effectively exert the characteristics of GMM.Based on the main performance parameters of piezoelectric ceramic speakers,the GMA bias magnetic field,prestress,cooling device selection,and the structural parameters of GMM rods and excitation coils for thermoacoustic refrigeration are designed,and finally the purpose of replacing piezoelectric ceramic speakers is achieved.(2)The finite element simulation analysis of the magnetic field of GMA for thermoacoustic cooling is carried out based on the finite element software.Firstly,the finite element model of GMA magnetic field for thermoacoustic cooling is established;secondly,the magnetic field uniformity is analyzed from the radial and axial perspectives of GMM bar;finally,the study of its influence on the magnetic field inside the GMM bar is realized based on the parameters of shell thickness and permanent magnet radius,respectively.(3)Based on the working principle of GMA,according to Newton’s second law,the first piezomagnetic equation and other principles,the GMA magnetic-mechanical coupled system model is established;then the coupled system model is numerically simulated to obtain the system’s parameter changes.Bifurcation diagram and corresponding displacement waveform diagram,phase plane trajectory diagram and Poincaré mapping diagram,and analyze the chaotic characteristics of the system;finally,the influence of parameter errors on the coupled system is studied.(4)Perform a detailed numerical simulation of the system,solve the GMA magnetic-mechanical coupled system equation by the fourth-order Runge-Kutta method,and obtain the bifurcation diagram of the system under different parameters based on the numerical solution,and combine the displacement waveform diagram,Phase plane trajectory diagram,Poincaré map and amplitude spectrum diagram are used to study the chaotic characteristics of the system when the equivalent stiffness coefficient,the secondary stiffness coefficient of the disc spring and the third stiffness coefficient of the disc spring change.The research in this paper realizes the design of GMA structural parameters for thermoacoustic refrigeration;establishes the vibration equation of the GMA magnetic-mechanical coupled system,and analyzes the chaotic characteristics of the system.This research has a certain guiding role in improving the output performance and stability of thermoacoustic refrigerators,and also provides theoretical support for the stability design of GMA.