Comparison of Stepwise Demagnetization Techniques

To demagnetize small-scale objects (dimensions less than 1 m) fabricated from ferromagnetic materials, it is standard practice to expose the object to a continuous ac applied magnetic field with a steadily decaying amplitude. For objects of dimensions greater than 10 m, there are problems of scale, and a stepwise procedure is preferred. We have simulated two different stepwise demagnetization techniques with a scaled model of a magnetic treatment facility regularly used in the deperming of military vessels. We used a steel tube as the model of a ship that was to be demagnetized. For each demagnetization method, we calculated the standard deviation in the final magnetization of the tube. This standard deviation provides a measure of how reproducible the results of the respective techniques are. We find that the standard deviation in final magnetization is improved by a stepwise anhysteretic demagnetization method over the conventional Flash D deperm procedure.