Method and apparatus for authenticating a record medium consisting of applying two different strength magnetizing fields and monitoring the remanent fields
US4038596A · kind A · utility
Assignee
Inventor
Key dates
| Filing date | Jul 2, 1975 |
| Grant date | Jul 26, 1977 |
| Priority date | — |
| Expiry date | Jul 2, 1995 |
Classification
- Technology area (CPC G)Physics
- CPC primaryG07D7/20
- WIPO fieldControl
- WIPO sectorInstruments
Abstract
Apparatus to examine a magnetic storage layer expected to contain a magnetic watermark includes means to magnetize the layer with a unidirectional field of a selected strength without saturating it and means to detect any distinct region of magnetic remanence. The apparatus may further include means to record the resultant remanence levels (or their ratio) for such a region and another part of the layer, means to magnetize the layer with a unidirectional field of a different selected strength, means to detect any then-existing such distinct region or regions, means to measure the remanence levels (or their ratio) for the then-existing such region and another part of the layer, and means to compare the measured and recorded levels (or their ratios) and indicate from the result of the comparison whether or not this represents a layer having a magnetic watermark of regions of distinctly aligned anisotropic magnetic particles. The use of different amounts of magnetization will produce different ratios of remanence in a layer having such a watermark but not in an homogenous layer.
Source: USPTO / EPO open patent data. Objective bibliographic and citation counts.