Multi-physics Coupling Analysis And Experimental Research Of Electromagnetic Acoustic Transducer(EMAT)

Electromagnetic acoustic transducer(EMAT) technology is a frontier and hotspot in the field of nondestructive testing currently. However, there has been no effective method to study the transducing mechanism and to optimize the structure for EMAT because of the complexity of multi-physical fields coupling, the nonlinear of magnetostrictive effect on materials and the limitations of FEM analysis tools and calculation method. Therefore, the FEM analysis of EMAT multi- physical coupling were studied, and the factors and interaction laws on the conversion efficiency of EMAT were simulated and analyzed based on the constitutive equation of magnetostrictive materials in this paper.Firstly of all, multi- physical coupling mechanism in the electromagnetic ultrasonic testing was analyzed, and the basic physics equations and processes of force-magnetic coupling in modeling the EMAT were introduced. Moreover, the adverse pressure magnetic matrix of material in different transducer structure was derived and the FEM of multi-physics coupling of electricity, magnetism, force and sound were explored.Secondly, the excitation, dissemination and reception of electromagnetic acoustic were simulated and verified by comparing with the experimental results based on the structure of steel EMAT. On this basis, the influence of geometry of bias permanent magnet on magnetostrictive amplitude and magnetic attraction force in EMAT was analyzed.Followed by above analysis, the influence of amplitude, frequency and pulses number of the exciting current produced in high-frequency coil, and the relationship between twining way of coil on magnetostrictive vibration and the steel sheets in EMAT was researched, for the sake of improving the conversion efficiency, the relationship between impedance matching circuits connected and excitation power box and high-frequency excitation coil, and filter amplifiers and receiving coil were designed and optimized.At last, the model of pipeline magnetostrictive T-modal guided wave sensor was established due to the actual need of axial flaw detection for piping stress cracking. The distribution and characteristics of static bias field, dynamic alternating magnetic field and magnetostrictive vibration were studied. The affects of applied stress on magnetostrictive transducer efficiency and propagation characteristics of guided wave were analyzed.