| 摘要 |
The objective of the present invention is providing autonomous timing labels for indicating the aging and expiration of a time period of products through gradual changing of their color. The color change can be coded to run, for example, from blue for newly produced products to red with product aging thus allowing easy monitoring, quick identification, and visual warning when the elapsed time approaches and reaches the recommended or safe use time. Said labels comprise thin films of photonic bandgap materials such as cholesteric liquid crystals containing photoisomerizable molecules that are transformed into the state of isomers possessing with finite lifetime with the aid of exposure of the material to UV light. The change of the reflection wavelength of the photonic bandgap material takes place according to changing concentration of said isomers as a result of spontaneous relaxation to their equilibrium state. Said labels can be reused by UV light exposure. The invention has wide applications for time coding of information carriers such as badges, telephone, credit, and gift cards, electronic keys, product labels, shipping tags, storage tags, parking stickers or oil-change stickers for cars, and other carriers of information that are changing as a result of use or storage, and compliance indicators for medical, health, security, and other industries.
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