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Anti-counterfeiting tags with camouflaged QR codes on nanocavities, using polymer-dispersed-liquid-crystals

Giuseppe Nicoletta, Mauro Daniel Luigi Bruno, Peng Yu, Zhiming Wang, Maria Penelope De Santo, Roberto Caputo, Antonio Ferraro

TL;DR

To address counterfeit products, the paper proposes a physically unclonable, smartphone- verifiable tag that hides a QR code in a polymer-dispersed liquid crystal layer atop a nanocavity metamaterial. The method integrates a randomly generated QR code with a MIMI-based optical cavity on PET and a PDLC layer using three nematic LCs (5CB, E7, 1825) to create a two-tier security system: the QR code becomes readable after heating to the LC transition, and the nanocavity provides distinct reflection/transmission colors. The authors demonstrate fabrication by DC sputtering the metal/oxide stack, laser printing the QR code, and drop-casting LC mixtures, followed by durability tests including water immersion, bending, and thermal cycling. The results show robust, cost-effective tags that can be integrated into packaging and offer multi-parameter authentication without specialized equipment.

Abstract

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.

Anti-counterfeiting tags with camouflaged QR codes on nanocavities, using polymer-dispersed-liquid-crystals

TL;DR

To address counterfeit products, the paper proposes a physically unclonable, smartphone- verifiable tag that hides a QR code in a polymer-dispersed liquid crystal layer atop a nanocavity metamaterial. The method integrates a randomly generated QR code with a MIMI-based optical cavity on PET and a PDLC layer using three nematic LCs (5CB, E7, 1825) to create a two-tier security system: the QR code becomes readable after heating to the LC transition, and the nanocavity provides distinct reflection/transmission colors. The authors demonstrate fabrication by DC sputtering the metal/oxide stack, laser printing the QR code, and drop-casting LC mixtures, followed by durability tests including water immersion, bending, and thermal cycling. The results show robust, cost-effective tags that can be integrated into packaging and offer multi-parameter authentication without specialized equipment.

Abstract

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.
Paper Structure (3 sections, 5 figures)

This paper contains 3 sections, 5 figures.

Table of Contents

  1. Introduction
  2. Experimental section
  3. Conclusion

Figures (5)

  • Figure 1: (a) Polymer Dispersed Liquid Crystal (PDLC) hidden QR code (b) visible when inducing nematic-isotropic transition rubbing hands. (c) After the transition temperature, the QR code, which represents the first encoding level, can be read using a smartphone. (d) Further, the second encoding level can be validated optically in reflection and transmission mode.
  • Figure 2: a) Numerical reflection (red line) and transmission (black line) of the optical nanocavity composed by Ag (30nm), ZnO (150nm), Ag (30nm), ZnO(30 nm). b) and c) show a tag produced with sputtering on a flexible substrate in reflection and transmission mode respectively. (d) Related CIE 1976 of simulated transmission and reflection with the corresponding points.
  • Figure 3: Schematic representation of the PDLC TAG. The PDLC and the adhesive layer are separated from the other parts of the TAG to show the position of the QR code.
  • Figure 4: Snapshots of PUF with (a) TAG 5CB, (d) TAG E7 and (g) TAG 1825 at room temperature where QR codes are not visible; (b) TAG 5CB, (e) TAG E7 and (h) TAG 1825 at transition temperature respectively with QR code reading, in reflection mode; (c) TAG 5CB, (f) TAG E7 and (i) TAG 1825 in transmission mode.
  • Figure 5: a) TAG E7 immersed in water. The process was repeated 20 times and integrity was verified. TG E7 on the mechanical elongation system, where the tag has been repeatedly stretched 30 times. c) TAG E7 on the hot stage. It was heated and subsequently d) cooled 50 times.