Security Device with Covert Images
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United States of America Patent
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Issued Date -
Dec 17, 2015
app pub date -
Feb 13, 2014
filing date -
Feb 19, 2013
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Abstract
A security device comprises a transparent substrate having an opacifying layer disposed on at least one surface. A reflective grating layer comprises one or more arrangements of grooves, and a liquid crystal material layer is disposed over at least a portion of the grating layer. The arrangements of grooves have a groove spacing such that liquid crystal molecules within the liquid crystal material layer are substantially aligned so as to polarise optical radiation passing therethrough. The security device further includes apertures formed in the opacifying layer and the grating layer comprising a transmissive diffractive optical element (DOE). The security device thereby comprises a transmissive security feature, visible when viewed in transmission mode by the naked eye, in combination with a covert, reflective security feature, visible only using a suitably oriented polariser.
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