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Proceedings Paper

Novel lock-in amplifier for identification of luminescent materials for authentication
Author(s): Alastair D. McAulay
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Paper Abstract

Digital and analog design approaches are reviewed for handheld low-cost electronic signal processing boxes for close-up optical detection and identification of phosphor markers for authentication of paper money, legal documents, pharmaceuticals, clothing materials, and military friend and foe identification. For extending the range to longer distances of over a meter (several feet) we propose a novel low-cost handheld lock-in amplifier that uniquely identifies a phosphor at a distance of several feet in a noisy environment of daylight, sunlight, electronic noise and reflection of the stimulating beam. The lock-in amplifier differs from a conventional one by sampling the detector out of synchronization with the source to avoid reflections which will mask the phosphor luminescence and provide opportunities for counterfeiters. The luminescence decays slowly after stimulation is removed. We simulate the lock-in amplifier to determine the trade-off between speed of authentication and distance. Only 40ms of integration in the lock-in amplifier will block noise of frequencies differing by more than 1% from the modulation frequency to allow authentication over a meter.

Paper Details

Date Published: 7 May 2007
PDF: 8 pages
Proc. SPIE 6567, Signal Processing, Sensor Fusion, and Target Recognition XVI, 65671I (7 May 2007); doi: 10.1117/12.720788
Show Author Affiliations
Alastair D. McAulay, Lehigh Univ. (United States)

Published in SPIE Proceedings Vol. 6567:
Signal Processing, Sensor Fusion, and Target Recognition XVI
Ivan Kadar, Editor(s)

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