| 摘要 |
An apparatus for optically detecting a security thread embedded in a paper-like material, e.g., a paper currency. The paper-like material is carried through a detection region defined by an infrared radiation source and two infrared radiation detectors. Two optical filters are mounted on the detectors, respectively. Those filters have different infrared transmission characteristics. Therefore, one detector can detect infrared rays having wavelengths only within a specific range determined by that one filter, and the other detector can detect infrared rays having wavelengths only within another specific range determined by the other filter. When the infrared radiation source projects infrared rays to the paper-like material, the detectors deliver the respective detection signals. A processor processes these detection signals to determine whether or not a security thread is embedded in the paper-like material and also what a detected security material is made of. |
