Electricity: measuring and testing – Magnetic – With means to create magnetic field to test material
Patent
1995-05-15
1997-03-25
Snow, Walter E.
Electricity: measuring and testing
Magnetic
With means to create magnetic field to test material
235449, 209534, 194318, G01N 2772, G01R 3312, G08B 1324, G06K 708
Patent
active
056148240
ABSTRACT:
A security thread for use in a paper-based value document, such as currency or banknote paper, includes a plastic substrate coated with one or more regions of "soft" magnetic material. A device for verifying both the authenticity and the denomination of the document includes a coil that is driven by an alternating current to thereby provide a uniform magnetic field within a predetermined spatial region. As the document passes in proximity to the drive coil, the applied magnetic field saturates the regions of magnetic material on the security thread. The magnetic regions provide a response magnetic field that, because of the saturation of the magnetic regions, is a non-linear response containing a multiple of frequency components, including a component at the fundamental or drive frequency and various harmonic frequency components. A receive coil senses the response magnetic field. A signal processor connected to the receive coil utilizes the response signals at the fundamental frequency and the low-order harmonic frequencies to determine both the type of magnetic material on the security thread and the denomination of the document from the spatial distribution of the magnetic regions on the security thread.
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Ager Colin
Dames Andrew
Ely David
Crane & Co., Inc.
Kosakowski, Esq. Richard H.
Snow Walter E.
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