Detector for a security thread having at least two security detection features

摘要

A security thread for documents such as currency and banknote paper comprises a plastic substrate coated with a plurality of discrete metallic patterns of electrically-conductive material, such as aluminum. The metallic patterns are arranged on the surface of the thread to indicate the particular denomination of the currency paper. The thread is typically embedded entirely with the currency paper. A first embodiment of a verification device determines the authenticity and denomination of the currency paper by counting the number of conductive metallic patterns on the thread and comparing the count to various count ranges. A second embodiment of the verification device scans the thread in a narrow-edge direction such that it simultaneously encounters all of the conductive thread segments. Capacitive coupling of an oscillator signal into one or more sensing pads result in an electrical signal having a distinct pattern. This signal is compared to a plurality of signals stored in memory that are indicative of valid thread denominations.