In magnetic fluxleakage testing, the testing signal decreases as the testing velocity increases. To explain this phenomenon, the change of magnetic field inside a steel rod under suddenly changed field is studied. When conductive metal experiences a sudden change of external magnetic field, the magnetic field inside the conductor will lag behind the change of external magnetic field. In order to calculate the lagging time, a model of conductive rod magnetized by a coaxial coil is built. The distribution of magnetic field inside the conductor is obtained by solving the harmonic Maxwell’s equations. The sudden change of magnetic field is simulated by rectangular waveform excitation. The rectangular wave is decomposed to harmonic waves by Fourier transform, then the time domain response of magnetic field is obtained by inverse Fourier transform. The magnetic field responses for different parameters are calculated. The results show that the magnetic field on the conductor surface almost changes with external field simultaneously, while the time lag is strongest in the rod center. The time lag of magnetic field in the rob center approximately increases with conductivity and permeability linearly.
FENG Bo,KANG Yihua,TANG Qi,CUI Ximing
. Theoretical Calculation of Eddy Current Induced Time Lag in Magnetization of Steel Rod[J]. Journal of Mechanical Engineering, 2015
, 51(22)
: 135
-140
.
DOI: 10.3901/JME.2015.22.135
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