| 摘要 |
<p>A security thread (108) for use in a paper-based value document (104) 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 (120) that is driven by an alternating current to provide a uniform magnetic field within a predetermined spatial region. As the document (104) passes in proximity of the drive coil (120), the applied magnetic field saturates the regions of magnetic material on the security thread (108). The magnetic regions provide a response magnetic field that is a non-linear response containing a component at the fundamental frequency and various harmonic frequency components. A receive coil (124) senses the response magnetic field. A signal processor connected to the receive coil (124) utilizes the response signals at the fundamental frequency and the harmonic frequencies to determine the denomination of the document (104).</p> |
