Document authentication by means of exchange-anisotropic magnetic material

US4396886A · kind A · utility

Assignee

• BASF SE

Inventors

• Eberhard Koester · Bischofswerda, DE
• Joachim Hack · Ludwigshafen, DE
• Manfred Steuerwald · Bischofswerda, DE

Key dates

• Filing date: Dec 3, 1980
• Grant date: Aug 2, 1983
• Expiry date: Dec 3, 2000

Classification

• Technology area (CPC G): Physics
• CPC primary: G06K19/12
• WIPO field: Control
• WIPO sector: Instruments

Abstract

A process for authenticating recording media which are to be safeguarded against falsification and which possess discrete regions of an exchange-anisotropic magnetic material, by comparison of the polarity of a residual magnetization which is left over, because of the exchange anisotropy of the magnetic material, from a predetermined initial magnetization after exposure of the material to a specific temperature cycle and, subsequently, to a magnetic AC field which decreases to zero, with the polarity of a residual magnetization formed in the same way from an opposite initial magnetization, and an apparatus for carrying out the said process.