| 摘要 |
PURPOSE:To apply an AC magnetic field to a magnetic tape without using an oscillating circuit and to perform erasion with no noise generated, by revolving a columnar magnetic material containing N and S poles magnetized on the circumferential surface alternately in the circumferential direction. CONSTITUTION:Both N and S poles of one or more numbers each are magnetized on the circumferential surface of a columnar magnetic material 11 alternately along the circumferential direction. When the signal recorded on a magnetic tape 12 is erased, the material 11 is revolved toward an arrow (a). At the same time, the tape 12 is driven around the material 11 toward an arrow (b), and therefore N and S poles are applied alternately to the magnetic surface of the tape 12 to produce an AC magnetic field. It is possible to apply a high frequency magnetic field to the tape 12 despite a low revolving speed of the material 11 by setting the revolving directions (a) and (b) of the material 11 and the tape 12 respectively opposite to each other. Then it is naturally possible to change the frequency of the magnetic field by varying the number of magnetic poles which are magnetized to the material 11. |
