Importance

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Abstract

Method and device for detecting the presence or the absence of conductive indicia carried by a supporting substrate which together comprise a security document, for the purpose of ascertaining the genuineness, value or other selected characteristic represented by said indicia. The indicia material is electrically conductive. The detecting device includes a housing and a sensing circuit including a source of high frequency a.c. alternating signals, first and second electrodes and the a.c. source coupled thereto. A carrier for the document is arranged in proximity to said electrodes. The questioned document is placed in the vicinity of the electrodes whereby the presence of the conductive encoding indicia serves as a coupling mechanism between the electrodes for capacitively inducing a secondary a.c. signal from the first electrodes to the second which is different from the first mentioned a.c. signal, said secondary signal being of a selected measured magnitude representative of said presence and of encoding. The housing may be provided with a transparent cover so that the document remains visible during evaluation, and to assure good electrical contact over its area.

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First Claim