| 摘要 |
Method and apparatus are used to detect and identify coded patterns on articles such as bank notes, in the form of magnetic regions (e.g., small areas printed with ink containing magnetic pigment). The apparatus includes a mechanism for passing a given article rapidly past a scanning location where a "write" magnetic head and its associated circuitry applies one or more recording signals (of a suitably high frequency) to these regions. The thus magnetized regions are then immediately sensed by a highly sensitive "read" head. The circuitry associated with the read head selectively amplifies the high frequency signals recorded on the magnetic regions. This further improves the signal-to-noise (S/N) ratio. It then compares the phases of the detected signals with a reference signal fed-forward from the write head circuitry. This further improves the accuracy of detecting the presence or absence of magnetized regions. After a sequence of regions in a coded pattern on a given article has been detected, the detected pattern and corresponding signal levels are compared in a "decision" circuit with the known pattern and signal levels of a genuine article (bank note).
|
