Current controlled excitation based deperming protocol of naval vessels

Naval vessels acquire permanent magnetism due to continuous exposure of the earth's magnetic field. These vessels are periodically subjected to deperming process to reduce their permanent magnetism. In this process, the entire vessel is closely wrapped with copper wire in helical form and alternate linearly decreasing current is passed through the coil. However, the naval vessels show nonlinear reduction of magnetic flux density due to their ferromagnetic nature. The traditional method of linear excitation results in ineffective deperming process. In this paper, a deperming protocol is proposed using nonlinear excitation of current pattern. The analysis is done using finite element method in which trajectory following hysteretic model is used to show the effect of different current controlled pattern.