US Patent 7113690 - Nanometallic Grating For Anti-Counterfeiting

http://www.freepatentsonline.com/7113690.pdf

Holographic patterns and other special indicia are usually formed on credit cards and other sensitive items to ensure authenticity. However, as better counterfeiting techniques are developed better anti-counterfeiting techniques must also be developed. This patent brings anti-counterfeiting into the nanoscale by using a nano-grating to determine authenticity. Claim 1 reads:

1. An anti-counterfeit method using a nano metal grating, comprising the acts of: creating a nano metal grating on an object to be inspected, wherein said nano metal grating has been polarized; providing incident light to irradiate the nano metal grating along an incident angle, and wherein the incident light is composed of polarization light beams of different polarization directions, whereby the polarization light beams are able to be reflected by the nano metal grating or pass through the nano metal grating; and inspecting whether a reflection light is only observed along a reflection angle relative to the incident angle and whether a refraction light is able to be observed from the nano metal grating, wherein if the reflection light is only observed along the reflection angle and if the refraction light is observed from the nano metal grating, the object is genuine.