Marking and authenticating documents with liquid crystal materia

Details Marking and authenticating documents with liquid crystal materia Marking and authenticating documents with liquid crystal materia

1982-06-28

1985-04-30

McGraw, Vincent P.

Optics: measuring and testing

Document pattern analysis or verification

G06K 710, G06K 974

Patent

active

045140855

ABSTRACT:
Method and apparatus for authenticating documents such as government notes and currency, stock certificates, and the like by marking the document with an encapsulated dyed liquid crystal material and examining the document for unique optical characteristics of the mark. Reading apparatus for the document measures changes in reflectivity of the liquid crystal mark with changes in an electrical field applied thereto. In other embodiments, reflectivity is measured at a plurality of different wavelengths. In one embodiment, the dye absorbs in regions of the electromagnetic spectrum "invisible" to the human eye and the reading apparatus monitors reflectivity changes at these invisible wavelengths.

REFERENCES:
patent: 3480785 (1969-11-01), Aufderheide
patent: 3873813 (1975-03-01), Lahr et al.
patent: 4006414 (1977-02-01), Parker
patent: 4435047 (1984-03-01), Fergason

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