| 摘要 |
A sheet element, such as a banknote or other document of intrinsic value, incorporating an optical authenticating device comprising a thin film element, preferably in the form of a strip, or thread disposed within the thickness of the sheet element and having known characteristics of spectral reflectance and transmittance, and wherein in the region of a least part of the thin film element the sheet element is formed with a pair of superposed windows between which the thin film element extends so as to be visible through each window. |
