Research Of Conductivity Mechanism And Propagation Characteristics Of Ferroelectric Materials

Ferromagnetic materials are widely used in electric power,transportation,machinery and other industrial fields.With the metal material for a long time,the environment is bad,by a variety of impact,corrosion,temperature changes and other factors,making the metal inside the deformation,fracture and other defects,so the metal damage detection is very important.In this paper,the electromagnetic interference system(EMAT)simulation model was established by using COMSOL Multiphysics,and the transduction mechanism of ferromagnetic material was studied and the hardware system was experimentally verified.The main research contents are as follows:1)The simulation model of Lamb wave transducer with ferromagnetic material is established,and the variation law of Lorentz force,magnetostrictive force and magnetization force is studied.By comparing the displacement of Lamb wave force,Under the action of magnetostrictive effect,under the displacement and comprehensive action to analyze the dominant factors affecting the transduction mechanism.Based on the study of the working mechanism of electromagnetic ultrasonic transducer,the finite element model of Lamb wave based on Lorentz mechanism and magnetostrictive mechanism is established,and the coupling of electromagnetic field,force field and sound field of EMAT is realized.2)The simulation model of surface wave of ferromagnetic material is established,and the influence of surface wave and the direction of bias magnetic field on the surface induced magnetic field is studied.According to the surface wave in the detection of defects in the modal conversion and defect reflection echo characteristics and then determine the location of the defect to achieve defect detection;analysis of the defect signal frequency characteristics.The influence of the depth of the defect on the reflected and transmitted waves is obtained by simulation.3)Experiments were carried out under different magnetic field intensities.In the experiment,the receiving voltage of the steel plate corresponds to the total displacement,and the receiving voltage in the aluminum plate corresponds to the displacement under the Lorentz force.By comparing the amplitude of the A0 mode with respect to the amplitude of the received voltage in the aluminum plate and the steel plate,the dominant role in the transconductivity mechanism of the ferromagnetic material is illustrated.The detection of different defects of the standard welds was carried out by using the electromagnetic ultrasonic testing system.The signals with high signal-to-noise ratio were obtained by wavelet filtering.The transmitted waves of different defect types were decomposed by wavelet,and the results were analyzed.The proportion of the energy occupied by the point,the node energy as a characteristic value of the defect to identify the different defects.