有限要素法によるローレンツ型EMATの準非線形解析

概要

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A finite-element numerical model is presented to simulate electromagnetic acoustic transduction into a half-space of a ferromagnetic metal. The model deals with a two-dimensional electromagnetic phenomenon induced by an rf burst signal to a flat coil situated close to the surface ; a pair of permanent magnets, having opposite magnetization directions, applies a static field into the metal. The simulation requires four steps. First, the initial magnetic field is calculated, including the nonlinear initial magnetization curve. Second, after adding the oscillating magnetic field induced by the driving current to the initial field, the differential magnetic susceptibility is determined for each element in the metal with reference to its own initial magnetization. The minor hysteresis loop, not the main loop, relating the magnetic field and the magnetization is approximated to a linear relation-ship, since the burst signal is long enough. Third, the magnetic field and eddy current distributions are separately calculated using these susceptibilities. Finally, the Lorentz force distribution is calculated, which is the product of the interaction between the magnetic field and the eddy current. The longitudinal wave excited is found to be less effective, due to the susceptibility decreased by the oscillating magnetic field, than the shear wave excited, as observed in experiments.
一般社団法人日本機械学会の論文
1995-03-25