| 摘要 |
<p>PURPOSE:To enhance secrecy and to make alteration or forgery difficult. CONSTITUTION:A mixed layer 12 of low and high coersive force magnetic materials or high and low coersive force magnetic material layers 16, 18 are laminated on substrates 10, 14. A concealing pattern having unit period integer times as long as the actual gap length of a specific reproduction head is recorded on the high coersive force magnetic material and true data is recorded on the coersive force magnetic material with a wavelength longer than the unit period of the concealing pattern.</p> |
