| 摘要 |
An article comprising a transparent piano-convex base sheet having first and second broad faces, the second face being substantially planar and the first face having an array of substantially hem i- spheroidal microlenses thereon, the shape of the mic- rolenses and thickness of the base sheet being such that collimated light substantially orthogonally incident to the array is focused approximately at the second face. The article optionally further comprising a specularly reflective layer on the second face which renders the base sheet retroreflective. An optional layer of adhesive over t he reflective layer permits the article to be adhered to a document as a tamper-indicating, authenticating, and protective overlay. Special images can be formed within the article to en- hance the security provided thereby. Also, a method for forming such article s. |
