Optically variable form birefringent structure and method...

Details Optically variable form birefringent structure and method... Optically variable form birefringent structure and method...

2005-12-13

2005-12-13

Patel, Kanjibhai (Department: 2625)

Image analysis

Pattern recognition

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C359S002000, C356S365000

Reexamination Certificate

active

06975765

ABSTRACT:
An anticounterfeiting device comprising a surface relief structure having both diffractive and polarizing properties. Polarization of reflected light is controlled by the orientation and composition of a fine grating structure whose shortest period is substantially smaller than the wavelength of visible light; and diffraction is controlled by a longer period component of the grating structure having a second orientation. Presence and arrangement of the polarizing properties of the device are detected by illuminating the device with polarized light and viewing the reflected light, or by illuminating the device with unpolarized light and viewing reflected light through a polarizer. Because such a device is difficult to copy or reverse engineer precisely, the authenticity of the device can be judged by the presence and arrangement of the polarization properties and the diffraction properties in the device.

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patent: 5694247 (1997-12-01), Ophey et al.
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patent: 6822769 (2004-11-01), Drinkwater et al.

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