Counterfeiting poses an evergrowing challenge, driving the need for innovative and sophisticated anti-counterfeiting strategies and technologies. Many solutions focus on tags characterized by optical features that are partially or completely camouflaged to the human eye, thus discouraging scammers. In this paper, a QR code is laser printed on a thin plastic foil previously coated by a specific nanocavity consisting of a metal/insulator/metal/insulator (MIMI) multilayer. This metamaterial possesses unique features in terms of light transmission that are due to the specific design. A thin layer of polymer dispersed liquid crystals, fabricated incorporating specific nematic liquid crystals in a polymer matrix, is able to camouflage the QR code that becomes, then, readable only under specific thermal conditions. Three anti-counterfeiting tags were fabricated, each using a distinct LC with its own nematic-isotropic transition temperature. The peculiar combination of the unique optical properties of nematic liquid crystals and optical nanocavities results in the creation of a novel type of tags showing two different encoding levels. Stress tests including water immersion, bending test, and prolonged heating have been performed ensuring the long-term stability of the tags. The realized two security-level anti-counterfeiting tags are cost-effective, straightforward to manufacture and, thanks to their flexibility, can be easily integrated into packaging and products.

翻译：伪造问题日益严峻，亟需创新且精密的防伪策略与技术。众多解决方案聚焦于具有光学特征的标签，这些特征对人眼部分或完全伪装，从而有效遏制欺诈行为。本文提出一种在预先涂覆特定纳米腔结构的薄塑料箔上激光打印二维码的方法，该纳米腔由金属/绝缘体/金属/绝缘体（MIMI）多层膜构成。这种超材料因其特殊设计而具备独特的光传输特性。通过将特定向列相液晶嵌入聚合物基质制备的聚合物分散液晶薄层，能够实现二维码的视觉伪装，使其仅在特定温度条件下方可被读取。本研究制备了三种防伪标签，分别采用具有不同向列-各向同性转变温度的液晶材料。向列相液晶独特的光学特性与光学纳米腔体的特殊结合，创造出具有双重编码层级的新型标签。通过浸水测试、弯曲测试及持续加热等应力实验，验证了标签的长期稳定性。所实现的双重安全层级防伪标签兼具成本效益与制造简便性，且凭借其柔韧性可轻松集成于包装与产品之中。